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5-1-1935

Hormonal control of

Earl A. Rogers University of Nebraska Medical Center

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Recommended Citation Rogers, Earl A., "Hormonal control of lactation" (1935). MD Theses. 405. https://digitalcommons.unmc.edu/mdtheses/405

This Thesis is brought to you for free and open access by the Special Collections at DigitalCommons@UNMC. It has been accepted for inclusion in MD Theses by an authorized administrator of DigitalCommons@UNMC. For more information, please contact [email protected]. THE HOHMONAI-, C 0 1T THO L

o F LAC TAT ION

by

Earl A. Hogers

Uni versi ty of Nebre.ska College of

lvIedicine. 1935 To my dear friend Dr. Fred Fouts, who has been my inspiration from childhood on, and by whose help I have been able to continue my studies in the profession he has .- practiced so nobly, this paper is respectfully dedicated.

480721 HfDEX IUTJiODUCTION

Histology of the mamma.ry glands .•.•••.••..•.••. :p. 1

TUstogenesis of the YO.8.mmary g18.nds .••••••.... , •.•• 2

Development preceeding pregnancy •••.•.••.••.••.... 3

Development during pregna:ncy ••.•.•..•.....•.•••..• 4 DISCUSSION

Nervous VB. hormonal control ..•••...•.•..•.••••••. 6

Early experiments with aqueous extracts •....••..•. 8 Early experiments with lipoid extracts .•.•..•.•••• 9 Effects of the ovarian hornone •••.. , ..•.••..• , , .• 10 Effects of the corpus lutelL'1l hormone .•....•... , .• 13 Effects of the anterior pituitary ....•... , ...•.•. 17 ?rolactin and grov.rth ...... , •.•.••. 23 The role of the conms luteum •....•.. , .•..... , ..• 26 The inhi bi tioD of le.ctation .•..••••....•...•••.•. 29 The effect of suckling ••.•. , ...... •...•...... 31

Failure of to maintain lactation.~ .. , •• 3~ The 9ancreas and lactation ••....•...... • 34

Practical applications ••..•...... •••.•••.. ~5

CO}ICIlUS I 01TS • '" • !9 .. "II ••• " •••• ,. ~ • " II .. jI • " • ". !t ••• 'f • 0 .... , '" flO .37

Bibliograpl"1Y .. >l J) ...... !I ~.-. ~ •••••••• It. til •• It ~ •••••• o, .39 I

nrrRODUCTI01;r The mammary gland is an anatomi:::!al structure comrn.on to all mammals, and is the mediw~ for the nourismnent of the young for a varying period following intrauterine life. To synchronize the development and function of the mrunma.ry gland wi th the development and birth of the yaung requires a high degree of coordination bete-ween ovaries, uterus, pi tui tary gla.nd and mammary gland, which vdll be the subj ect of ·this paper. Each ma,jmnary gland in a WOI1an is composed of from 15 to 25 individual lobes rad­ iating from the ma.nuua.ry pa,pilla or and se)arated froID each other by layers of connective

tissue and . ~a.ch lobe is an ind­ ependent, compound, branched alveolar gland, hav­ ing a separate o]ening on the surface of the nipple by means of its excretory or lactiferous . The secreting portions of the gland, the alveoli, consist of a basement membrane, a layer of myo-epitheJ.,ial cells, (which serve to associate the 1I18lIJ.mary gland morphogenetically with the sweat glands) and a layer of low col- 2

UItlllar epi thelial cells. These latter elements secrete the complex product, milk, by diffusion of the constituents from within the cell into the lruuen of the

tending from the upper lir1b bud to the inguinal fold. Only a portion of each milk line in the costal region continues to thicken to form a pair of lens-sha.::;>ed plates, which later become hemispherical or club shaped thickenings pro- , jecting into the underlying dermts. These are ceclled narmnEtry buds t a,nd in 0 ther mammals a a number of such buds may form, or they may develop at different points along the milk line. Themarnmary buds give rise to a number of cell cohlmns from their lower surfE'ce, which project into the underlying connective tissue~ and later become lactiferous ducts. In man there are 15 to 25 of these primary sprouts. These give rise to secondary sprouts or cell columns which are the lJrimordia of the excretory ducts. :By enlongation and branchings the compI,ex duct system of the gland is formed.

At birth the mammary gland is 3.5 to CJ rom. in diarneter, and the lactiferous ducts have formed, with a few excretory duct branches. In males there is a regression of the gland, and only the rudimentary nip)le remains, with its surround- ing are~la. In females t:lere is a slow evolution 4

of the duct system throughout childhood to

puberty, when the whole process 1S spe(~ded Ul), the gland increases in size due to the deposit- ion of fat, the nipple increases in size, and the duct system becomes complete. There is no development of secretory portions until the advent of pregnancy. Then

there is a rapid multi~lication of the epithel-

hun at the ends of the excretory ducts, and the secretory alveoli or lobules are formed. This is especially rapid diring the first half of pregnancy, and is acconpanied by a loss of fat from the gland to make room for the secreting elements. During the last half of pregnancy mnl tilJlication of the epi thelia.l cells slows

down, and a secretion is formed in the 801 veal i, 'which is colostrur.1. In the first few' days after

delivery the colostruI:!. is re::;laced by milk, which continues to be secreted for the period of suckling of the child. {42, 2) In other animals the developnent of the ... marlY:J.E:ry glcmd at birth, before and a.t puberty varies somewhat from species to s)ecies. For 5

exam)le, in the ferret there is no duct develop­ ment even after 1Juberty, while there may be even

full lactation in some marSUl)i tale and pos~:;ibly the dog after oestrus. A full discussion of theBe differences is given by Turner (2) and may well account for a number of discrepancies in the findirl.cs of the various investieators to be discussed later. 6

In the past half century a great Yncmy investigators have directed their efforts toward finding the expla.nation for t:1.e erowth, develop­ ment and funct ioning of the maElmary gland. l'luch has been accomplished, 1:mt tl1ere is still much left to be explained. ~j:any discrelJancies have arisen beteween the findings of the various laboratories, all of which cannot be explained on the basis of specie differences, and there is much to be desLred in the way of standardization of methods and materials in the vErious centers of experimentation. Practically all the exper­ imental work has of necessity been done on laboratory animals, and the field of practical applications is still unlimited. Prior to 1895 physiologists believed that the coordination beteween the developing embr:io and the marm:nE;ry glcmds w[;s due to direct nervous connectin beteween the uterus and mall.TIn- ary glands. As evidence of this was cited the conml0nly observed COli.traction o:r: the uterus follow­ ing stimulation of the ni:Jples. (62, 2) In 1.':<'94 Eirinoff (43) observed that follovving the cOTIl}?lete 7

severance of these nerves in9regnant animals the gland would continue to develop and would secl"ete milk after parturi tion. '1'his was confirmed in 1,S96 by Gol tx and EWBld (23) who conrple~~ely I'emoved. • the IVlubar cord from a b1 tch. She subsequently conceived, and gave birth to a litter of puppies which she was able to suckle normally. Routh (57)

(189;~) observed that complete paraplegia below the level of the sixth dorsal vertebra did not inhibit lactation in man.

The nervous control was also disproven in another -way. Hibbert (53) (189l) was able to transplB.nt into the skin of the ear. During a subseqt:ent pregnancy the gland enlarged ,as usual, and lecta,ted following part'llri tion. Pfister ,( 52)

(1901) repeated the experiment on a rabbit.

On the other hand, it hed been sho-vvn by ](nauer (34) and :-Ial ban (24) (1900) tha t oophorecto::::1Y in young cmirlals would ceuse regress-

10n• 0_,-F' the YflBllmary glands, end they wou,ld not attain noimal pubertal size. That this wa~ not due to the severance of nervous connections they demon- 3trated by grafting the ovaries to the peri tonel1m 8

or intrEJuuscularly. '~Jhen this Wc~s done success- flL'-.ly the mEtll1uary glB.nds attained their norr1al pubel'tal growth.

Therefore it has been generally accept- eO. as true that the SOl,rce of stimulation to the ma1Yh'1l.ary glend is hor:t:lOnal, due to a "chemical messenger" (62) rather than nervous. This is true of the growth stbmlus; as will be seen later the lactation stimulus is held be some to have a nervous factor in its control. Subsequent investigations have been directed toward finding the nature and origin of the hormones responsible. for mamma.ry hypertrophy Fnd lactation. (1906) . were the first to attempt by experim.ental means to find the hornones respons i ble for maJ:n.. 1l18ry growth and lactation. They injected filtered aqu- eous extracts of placenta, fetuses, uterine tissue and ovaries, as well as combination~ of these into female rabbits. They did not castrate their animals, so the re,~ults they obtained WiJre prob- ably due to the rabbits own ovaries, and not the weak extracts they used, es,!?ecially since their figurer, show only [ duct development, similar 9

to that observed after reaching puberty. (18) Fran};: and Unger (18) (1911) repeated the experi~nents of Lane-C1aypon &nd Starling, a1 so with negative results. Other investigators in this period who used aqueous extracts failed to bet conclusive results, at best only a slight duct growth. I t has since been shovm that the tissues they extracted do contain the oestrus producing hormone, [mt the amounts extracted in aqueous solutions are very small. This fact, together with the fact t~at they failed to recog­ nize the necessity of I'emoving the ovaries, made ,,'{hat slight results they aChieved value­ less, since it Dight easily ha~e been a normal oestrus Growth. (2). Following the report in 1912 by Iscovesco (32) that lipoid extracts of the ovary,

COT)US luteurll and pla,cente., ca1Ase distinct. change s in the female geni tal tract a maIl11J1ary glands, this line of attack 'NElS taken up by several investigators. Fellner (21) (1913) obtained duct system growth in normal and castrate 2nale Emd female guinea pigs and rabbi ts.

~errmann (29) (1913) (30) (1915) obser~ed 10

growth of the manml8.ry gl&.. nd in castrate and normc.l female rabbi ts; Frcmk 8.nd Rosenbloom (19; (1915) slight 6rowth in castrate rabbits and rits. It has since been shown that the success of these men WGS due to their successful extraction of the oestrus producing hormone. (2) Since the effect of the ovaries on the mamrna.ry glands had already been observed by Xnauer (34) and Hal ben (24) it is only na.ttu'al that these oreans si10ulcc be sub,j e.cted to con­ siderable study as to a possible relationship to pregnancy developIGent. 1'11e experiments just mentioned, with lipoid extracts of the ovaries was a start, but the real impetus to this line of research was given by Allen and ')oisy (1) (1923) by the introduction 6f the rat test unit for the oestrus stimulatitlg hormone of the o'Varies, and the determination of the tissues in which this hormone is found in the greatest concentration. This hormone has been n8IYled by various investig-

ators "oes~rinll "theelin!; and "menoformon". Early in the investigations of the effects of theelin it was observed that one of its effects is on the maJ":1mary glEtnds. From that 11

tiue to the present this effect hES been Btudied

by a great ma.ny men, only 8 few of whom will be mentioned.

Ha.rt,.lc.:m, et a1 (28) (1926) produced duct system growth in the oppOSStl1.'1 by injections of folli cular and J)lacental horr:lOnes (theelin).

DeJongh (1931) injecting 20-0 units of menoformon per day into male guinea pigs produced marked groiivth of the mam:n1ary glands, and if the dose were suddenly reduced to 2 units a day trw glands secreted railk.

Turner, et &1 (66, 67, 68, 1930 & 1931~ using castrated immature ma.le and female rabbi ts and rats were able to produce only duct syste:'1 growth (pubertal development) by the injection of the oestrogenic hormone, whether obtained from the ovary, placenta., amnionic fluid or urine of pregnancy. In 1932 they used crystalline theelin and theelol (69) and produced signific- a.nt duct growth but no lobule fornation in the mammary glands of ruBle rabbits, cEstrated female rats and male mice. No difference was observed beteween the effects of theelin and theelol. 12

B rad' Dury (7')' ings in the.mouse. He found that the sexually mature glEmd consisted only of ga,lacto phares (prim.ary duct system) and that injections of theelin had no effect on this gland. A similar duct growth could be brought about in castrate immature meles and females, however, by the injection of theelin. From the above experiments it seems clear that the ini tial development of the marnInc:,ry gland is under the tnfluence of theelin. This hor.;none, produced by the ovary, stimulates the pubertal clevelolxnent of the duct system, which ll}ay continue to .develof during e8.ch oestrus cycle. Theelin secreted by the placenta may cause the initial increase in the duct system during pregnancy. This hormone seems to be ineffective in stimulating lobule formation in most species, however. In the guinea pig apparent- ly lobules may be formed by admini stel"ing large doses of theelin, for secretion is obtained when the dosage is reduced. (14) In other animals a d ight lobule may be noted at times. (2, 13) But this slight lobule formation does not begin to 13

CD mpare I'd th the rapid hyperple.sia which OCCU1~S during the first half of pregnancy, and therefore an addi tional hormone h£lS been sought which vlould stimulate pregnancy hyperplasia. It is only natural that so prominent a structure as the corpus lutetml should be subj ected to some study. Starling (62,36) and Frank and Unger (18) used aqueous e:;:tracts of this gland, but as has been previously stated their extracts were too weak to have any effect. Iscovesco (32) and Fellner (21) were more successf~l with lipoid extracts, but we have already mentioned that they extracted theelin from the gland, and not the corpus luteu~ hormone.

The discovery in 1911 by Ancel 8 .. Tld :Bouin (3) of the condition of pseudopregnancy in the rabbi t gave the corpus lutel-un angle a fresh impetus. The rabbit does not normally ovulate until copulation occurs, hence cOrlJOra lutea are not found except in the pregnant condition.

By mating does YlJi th VElsect;omized bucks they were able to induce ovulation cmd corpus luteum format­ ion in the non-pregnant animal They found that the corpus luteuI:1 persisted for about 15 days, 14

about half the c~urgtion of a normal pregnancy. During this time the mammary glands underwent rapid lobule hyperplasia, so they were convinced that the cttrpus lutelli'll is responsible for the devel;')pment of the me.JTh'nary glands during the first half of pregnancy. They ascribed the development of the mammary gle.nds during the latter half of pregneney to the so-called ilmyo­ metrial gland tl .(4) However, riallTIllond (26) (1917) showed that this structure is not constant, being found in only an occasional rabbit, and not at all in other species. He also pointed 6ut that the corpus luteum persists throughout normal pregnancy, and concluded that the d.evelopment of the mamynary gland during the lE,tter half of pregnancy is due to the same factor which caUses its development in the first half, namely the corpus luteum. In 1930 Corner (13) by using a highly potent extract of m rpus luteuro, (progestin)

WE;S able to carry pregnant does to full term Which had b'een deprived of their ovaries Vi hours after conception, a proceedure which othervlise resul ts in abortion. In these rabbits maramary 25

growth and lactation occurred normally. He

reasoned that if' the porpus lutetlln of pregnancy were respons! ble for marmT.lary gland development, he should be able to produce similar develo.pment in spayed non-pregnant does by injections of progestin. He made this test, but could produce no changes in the gland. However, these rabbits were deprived of oestrin, since they were spayed, and it had been pointed out by T{issau (31) (1929) that the corpus luteum does not exhibit its effects on the symphysis pubis and endometrituu wi thout the immediately previous action of oestrin. So Corner used Ghe method of Jares (33)(1930) to subject the rabbit to the continued action of both oestrin and progestin, namely, inducing OVUlation and new crops of corpora lutea at of a few days by intravenous injections of 10 c.c. of filtered unine of pregnant women. ITe found that continued action of progestin even when preceeded by the action of oestrin does not induce proliferation or lactation in the mammary gland. Turner and Frank (67) (1931) found that 16

inj ections of progestin in imraature male and fema.le castrate rabbi ts produce no changes in the mammary glands, even when l')receeded by inject- ions of theelin. Realizing that during pregnancy a large amount of theelin is being secreted by the placenta, they attempted to duplicate this by inj ecting la.rge doses of theelin in their rabbits simultaneously with their progestin injections. '\ By this method they obtained a full development equal to that during pregnancy. Bradbury (7) (1932) made simJ.lar fi nd- ings in the mouse. He found that lutinization of the ovaries by means of injections of pl'egnant women's urine causes mammary hyperplasia, but not if the ovaries are absent. 3e1ye, et al (58) (193:'1) confirmed the above findings in the rat. They foune). that intense lutcinization of the ova~ies produced by injections of pregnancy urine causes mammary gland growth. Nelson and ?fiffner, (45, 46) (1930, 1931) found marked hyperplasia. in the glands of immatul'e male and female guinea. pigs and young male rabbits which were injected with only a • 17

corpus luteu..."U extract. Turner (2) has pointed out, however, that their extracts probably contain­ ed oestrin as well as progestin. At this point it would seem that m81n.zuary gland growth in most cmimals is caused by the action of two hormones, oestrin initiating duct system growth, and oestrin plus 9rogestin causing lobule formation. As we shall see la.ter the corpus luteum problem is not nearly so easily settled as that. So far we have purposely avoided the problem of secretory activity , for it is in connection with this function that the most im­ pDrt&nt discoveries with regard to the hormonal control of lactation were In.ade. r,9_ne-Claypon and Starling (36) concluded that the substance which gives the growth stimulus to the ma,Ir]rnary glands inhibits their secretory activity by direct action upon the secreting cells, for the reason that a cell cannot be both growing and secreting at the same time. This view was held by many of the subsequent investigators. Evidence sl;rpporting this idea, G"side from the clinical evidence that these early 18

investigators based their tclee.s upon has been put

forth by DeJongh and DingeInanse (14), I in their vvork viii th guinea pigs previously mentioned. I,actation was noted when the amount of oesGrin injected was suddenly reduced, just as occurs at partur- ition following expUlsion of the placenta.

Also, Selye et al (58) noted lactation in rats following the removel of the ovaries which had undergone intense luteinization under the influence

of pregnancy urine, and had been accompanied by

maJ,.~ "nm""rv,it,,&,.U... O,. .) G<7.L~"''''' UJ..l U.rl gro'''''thIit,!., • However, lactati1n did not occur if the pi tultary gland v"rere absent, and that could mean only one thing, that the pituitary has some role in the hornonal control of lactation. In 1924 3vans (15) had sho-vm that inject- ions of an alkaline extra.ct of the anterior lobe of the hypophysis would cause persistence of pre- existing corpora lutea as well as causing intense luteinization of Gra,afian follicles wi thout ovulation. Using the r:lethod of EVans, Parkes (51) in 1929 injected such an extract in pseudo- )regnant rabbits and was able to continue the

luteal phase beyond the usual 15 day period. 19

In the,se animals he obtained a growth of the mamm­ ary glands equal to full term pregnancy, and therefore decided that the corpus luteum: was responSible. 3ut Corner(13) using the method of Jares (33),that is, pregnancy urine injections, could note no change in the mamm.ary glands al th­ ough luteinization of the ovaries was produced equally as well as by the anterior hypophysis

extracts. ~Ie ass1.uned that some other factor must be present in the anterior hYPollhysis extracts

Vihi ch W80S respoBsi ble for the meJ:nmary gland growth obtained by Parkes. He then injected spay­

ed virgin rabbits with alkaline ex~racts of the anterior pituitary gland, and obtained bath hyper­ plasia and secretion in the mam:r.J.ary glands. His rabbits were mature, but virginal, the mruwaary glands having reached the pubertal state before the injections. Stricker and Grueter (64, 65) (1928 & 1929) had a.lso been able to produce m(?,,rel;."'ll&ry hyperplasia and lactation in rabbits by the injection of an aqueous extract of the anterior hypophysis. They obtained their results first by injections in the latter part of pseudopreg- 20

nancy. Later they removed the ovaries on the tenth day of pseudopregnancy and were still successful, indicating that t11e ovaries were not responsible for their results. Still later they learned that it was not even necessary that the animal be pseudopregnant, but it was only necessary that the mammary gland be developed by previous pseudopregnancy or pregnancy. They were successful under these circulTIstances in producing lactation in rabbits, dogs, hogs, and cattle by their anterior pituitary extracts. They could not induce lactation in virgin rabbits. Shortly after Corner (13) had published his work, Riddle (54) (&931) and his associates who were studying the physiology of reproduction in birds, found that some of the extracts of the anterior pituita.ry which they were injecting to determine their effect on the reproductive system of pigeons, also caused an enlargement of the crop glands. These are two dorsa-lateral areas in the crop of pigeons and doves of both sexes which 1'10rmally cannot be differentiated from the rest of the era) mucosa, but which undergo remark­ able hypertrophy at the end of the brooding period, 21

and produce by secretion Emd desqumaation of the mucosa cells a substance c~lled crop milk. This is mixed with partially digested food in the crop and regurgitsted to feed the young. This process is analogous to lactation in that it represents a phase of reproduction consequent to ovulation, occuring at a considerable time afterward, and at the time of a new phase of alimentation in the young.

Riddle (54) determined that this gro1,vth occurred after;,.Jrevlous section of the nerve supply, so it could not be conditioned by nervous control. ~e was able to produce crop glano_ growth by inj ections of anterior pi tni tary e::z:tract s, but not by pregnant urine. TIe was un- able to determine whether it was e¢ther of the two known hormones of the anterior p{tuitary (growth, b"' sex ma-urlt . t'y; W.~lcn}., was responSl. ~e, or a th'.Ira, , unknown hormone. --Ie suggests tha.t the crop gland response r:light forn a convenient I!leanS of stande.rd- ization of the hormone responsible.

A. ye&r .Le~ t er .ttl-'d~l u. e 1-5'I.;) ) YfaS abie to st;;:'cte that the horlOne respons i -ble for the crop clbnd response is a Sep&r8.te hor~Ilon'e, which vlTOuld 22

still produce this response when freed of the growth and sex maturity fractions. Ye gives the nethod of making such a separation, and pro)oses the name II prola.ct in H for the horE10ne. He found that male and female mature guinea ;;;i6s and matul~e female rabbits would also respond to this hormone by lactation; the I'lales after previous treatment with theelin and progestin. Lactation began 2 to 3 days after beginning the treatment in rabbits, 3 to 5 days in guinea pigs. The term and qua.. nti ty of secretion were highly va.rie.ble. In all cases (pigeons, guinea pigs, rabbits) the gonad-s:imulat- ing principle and growth principle, wh*n freed of prolactin, failed to give any le.cta-tion or crop gland response •.

In a- subsequent publication (56) ( 1933) Riddle gives very c:nu]lete and extensive e: :periment­ al data. which shows that prolactin is a separate hormone; that it is capable of producing the crop gland response in doves amI pigeons and the lact­ ation response in guinea pigs, rabbits, rats, OppOSS1J.lli and monkeys; that the growth or eonad- stimulating hormones are incapable of doing this; that prolactin is ef!'ective in castrate and hypo- 23

physectomized animals. He also gives detailed directions for the preparation of prolactin and its assay, using the croJ gland response. In a recent arti cle (6) (19;)4) he hees shown th2t the hormone prolactin is a protein substance, digest- eO. by ~Grypsin. All the investigators who have used prolactin or similar preparations of [:;11.e an terior pituitary are agreed that it does stimulate lactation under the propet conditions. ~ere the agreement stops. Some men have held that it not only stimulates lactat ion, but it al so promotes gland grovyth (lobule formation;. There is also a difference of opinion as to whether oestrin anly is sufficient to prepare the gland for the action of )rolactin, or whether prot"estin also is need- ,-: ed. I~e will first consider the problem of prolactin and gland growth. This difference of opinion came up in the earliest envestigations. It will be remember­ ed that Corner (13) found both hyperpla.sici and secretion to result from prolactin injections in his rabbits, while Dtricker and Grueter (64, 65) were unable to produce lactation in v1:t'Bin animals, 24

but only if the mammary glcmds hacl been previously developed by pregnancy or pseudopregnancy.

Nelson (46~ (1931) suggests that the ovarian factors (oestrin end progestin) are respon­ sible for the early growth of the mammary glands, end that the profo-,;nd growth during the latter part,)of pregllattcy is controlled by the anterior pituitary. Asdell (5) (1932) found that potent lactogenic extracts are without effect in i:m:m.ature rabbi ts. ~Ie produced full mammary development in ovariectomiz,ed ra.bbi ts which were just mature.

Catchpole et a.l (38) (193~) found that the .mam..'1lary glands of rabbits respond to the lactation hormone by both duct and alveolar growth, end lc:ctation. ';,ei chert (70) (1934) found that the ovariectomized rat does not respond to the lactogen­ ic hormone, but when the ovaries are present, respond by both growth and lactation. On the other hand, Riddle (56) (1933) states that "we have become fully convinced that prolactin has not in the least favored the growth and development of mammary tissue in the 25

individuals with which we have W'orked fl • (Guinea pigs and rabbits.) The latter view is hel(l by 1'urner and his associates. Garner and Turner (22) (1933) could produce no growth of the marmnary glands by pro­ lactin injections in youna; ovariectomized rabbits.

Turner (2) cites unpublished d&.ta by Gt~_rner, in which they not only failed to get duct growth in iznmature g1c.mds, but also they failed to get lobule formation where ducts only were present.

IUs explanati on of the a:pparently posi ti ve results of others is a logical one. He thinks that in all cases where lactation is produced by inject­ ions of prolactin, lobules were already present, and the apparent hyperplasia is only a distention of the lobules by secretion. It has been shovm that in some mature animals ~J few lobules may be present. This would explain the onset of lact­ ation in such animals. In immature anim,31s and males lobules would not be found, and in these no one has been able to produce lactation without previous treatment with ovarian hormones. Lyons, et al {B7, 9,:39i Nelson et al (45,46,47,48,19,50) Bradbury (7) Asdell (5) EVans (17) • 26

Some such explanation as given by Turner is necessary, for certainly in the normal pregnant animal secretion and growth do not occur simultaneously, but rather in sequence. Helson (50) has suggested that perhaps the anter­ ior lobe hormone acting together with the ovarian horY!lOnes promotes growth, but lowering the oestrin level (removal of the place~ta ) allows the anterior 101Je horIilone to stimulate secretion. This would apparently be refuted. by the normal development(but failure to lactate) of mammary glands in hypyphysectomized pregnant animals.

Selye et a~ (59, 71) In considering the preparation needed before the ma1l1.t'llary gland can be stim.u1ated to lactate by the action of prolactin, we find a consiclerab1e controversy over the role played by the corpus 1utemn., Corner (13) thought thB.t the corpus luteuiTl is unnecessary, since he used spayed virgin rabbits in which he thinks it highly unlikely that corpora 1utea ever existed. Stricker and Grueter (64, 65) thought previous sensitization by the corpus 1uteum is necessary, since they could not 27

produce lactation in virginal rabbits. De Jongh and Dingemanse (14) produced lactation by injections of oestrin in male guinea pigs, so evidently progestin is unnecessary in that anhlal. Nelson

( 49) eli d the S[cln.e, except that he followed the oestrin inj ections wi th ~)rolactin in'order to obtain lactation, instead of reducing the dosage of oestrin. It would therefore seem that the corpus luteruTI is not necessary in the guinea pig.

Catchpole and I,yons (8~: found that no previolls corpora lutea are necessa.ry in rabbi ta, but that lutein sensitization makes them more reactive to prolactin. They saggest that the ovaries which ~o not show evidences of corpus lutemTI formation do contain tlleccl lutein cells which normally go to make up the corl)Us luteum, and thin'S: that these cells may be a factor in preparing the gland. Asdell (5) found that the cor )US lutetun is not necessary for the lactation res)onse in the rabbit a.nd state that a goat Which had never been in heat was made to lactate by ?rolactin injections.

On the other hand, :Bradbury (7) finds that in the monse the lactation hormone is not effective unless alveoli forma.tion has been produced by luteinization of the ovaries by means of ~Jregncmcy urine. Also, EVans and Simpson (16) find that in spayed mature virgin rats it is impossible to produce ffiELlY'.Jnary and growth and secretion by means of prolactin injections, even if progestin also is

gIven.• 't-.Helcner " t e".l.. a 1 (70\ \J can f'lr"le ~ d t'..'lese lIn·0' d - ings, but were able to )roduce gland growth in

the absence of the ovaries by properly propor- tioned injections of ovarian hormones (oestrin and progestin). They point out that this is a distinct species difference. That there is a

,- distinct species difference in the necessity for the previous sensitization by probestin is (71) also pointed out by Nelson (50) and Selye et al \ . It would seem therefore, that prolactin is the hormone secreted by the anterior hypop)1.ysis which initiates lactation. It probably does not promote lobule formation. It is capable of act- ing on a gland only if the gland has had lobules

previously formed. There is a~ecies difference in the matter of lobule formation. Some animals

mB.y form lobules under the influence of theelin aloDe, others require the action of progestin also.

:"ro bably both horm.ones Ellay 8 pert in norm.al pregnancy. 29

~Ne have not 2S yet considerec!_ why 18"ctation occurs only at the termination of pregn&ncy. It seems to be quite generally acce;;ted tha.t it is the antabonism of theeli.n that prevents lactation. Nelson (5~) as well

'c'·",,; 1 as ·ill 1 . th ana Qb~ ·tIl_ (61 \ \ ) were a b ~e t 0 1n3101 . 1 . ., . t S .. lactation by injections of theelin •• Nelson(50) has sho'vm also that it is the theel in secreted by the placents which inhibits lactation. He did this by castra.ting;;regmmt guinea pigs and having them go to full term, only lactating after parturition. Since mammary and growth occurred normally there must have been a source of theelin. Removal of the pregnant uterus dic. not cause lactation, it the ovaries 1;V8re lett, but removal of both resulted in lactation. Removal of the ?regnant horn of the uteruB and the ovaries leaving the sterile horn resulted in lactation, therefore ~ some factor aside from the uterus was responsible. Removal of the foetuses and ovaries, leaving the placenta did not result in lactation as long as the placenta was retained. Therefore the placenta must elaborate the theelin \'ilhich inhi bi ts ICoctation. That retention of the placenta will in- 30

hibit lactation has been observed a number of times. Smith and SJ!lith (61) Stimson (63) 1'ra,nsplanted :placental tissue will do the Same, as long as the grafts are active. Fran"d (20) , So then, lactation occurs at the termin- ation of pregnancy because the oestrin or theelin content of the blood falls, due to the loss of a source of this hormone, the placenta. Eut how does the presence of oestrin inhibit mammary activity? Nelson (50) believes it is by an action on the anterior pituitary, preventing the release of prolactin. ~hen thes inhibitory factor ~ rmnoved, the anterior pituitary secretes prolactin.

Thi sis shown by the f~wt that simul ta.neous inj ect- ions of oestrin and prolactin result in lactation in a properly prepa,red animal. On the other hand, he thin:{s that +arge amounts of oestrin may act directly on the :uamrJl8ry glo"nd itself, for if a large amount of oestrin is injected together eith a corresponding dose of prolactin, no 18ct- ation re8ul ts. tie sugges t that this problem could be clarified considerably, as well as the

,9roblem of the role of lJrolactin 011 mammary development during })regnancy. b;';T some ae&.l1S of 31

devermining the amount of )rolactin in the blood of a pregnant animal. Tl,!e fact that mamnary: deveJ.o}?ment may continue in an hyppphysectomized pregnant anim.al does not necessarily preclude the possi~ility of the pituitary being responsible in part, for there are fetal hypo~)hyse S -,-vhi ch might secrete prolactin. Another puzzling finding is that of Selye et al (12, 71 J who state that pregn8.nt, hypo)b.ysectoEli zed rats and mi ce secrete millt for a few hours after pa.rturi tion. ',.e would be inclin- , ed to attr*bute this to fetal hypophyseal hormoneB circulating in the blood of the mother,but they a.lso find (71) th8t distention of the uterus with )araffin prevents this secretion. The:)r postUlate a. nervous influence on the hypophysis by the pre8ncnt (or distended) uterus, 1nhi bi tL1.g the release of prolactin. They ascribe the secretion of milk for a few hours after parturition in their l1.ypo)hysectOl'l1ized animals to 8. functional stimulUS to the m8111ITlary gland by the uterus.

Another controversial ma;~ter is that of a possible nervous influence on the pituitary by the act of suckling. It would seem that the exper- 32

iments of Mirinaff (43), Ewald (23), Routh (57) Ribbert (53) and Pfister (52) previously mentioned

should be enough to di sprove any po ssi -bi 1. i t:)T of a nervous control. Although HamlrJ.ond (27) found that ""hen the

teats of certain marn.'11ary glEmds of a, rabbi t were occluded to prevent the young from sucJding the corresponding g18.nds would undergo involution,

even when adjoining glandd were i~ an active state of lactation; and :\felson (50) found exactly the same to be true, Selye et al (60, 71) found

exactly th~ opposit. They tied the galactophores of a gland, and it remained filled under the

stimulus of suckling. ~'TIxcisinc; the nipple of one gland and allowing the opposit gland to be sucldid, they found that the gland which was not suckled due to the absence of a nipple remained

in active lactation~ They take this to mean that the act of suckling by means of a nervous stimulus to the hypophysis causes the release of

prolactin, which conti~ues to stimulate lactation in the ma.mrnary gland that is not being suckled. Evidently more wo r}£ needs to be done to cllil,rify this point. It seems that it would be easy to 33

settle this question by seeing how long a glEnd could be ke11t secreting under the influence of prolactin injections-but without being drained, for the whole matter hinges about the question as to 'If/hether mere distentLm. of the gland by re­ tained secretions will result in its involution, or whether the absence of prolactin is necessary. But that experiment cannot be satis­ factor<'jlly carried out because of another puzzl­ ing finding, namely that continued injections of prolactin are ineffective in continuing lactation, even when increa~ingly large amounts are injected. ~iddle (56) states "it seems, thov.gh it is not proved, that ini tial light dosc:ge with prolactin develops in castrate female guinea pigs a mamnlH.ry state in ','Vhich the lactation response is unusually diff±cult to obtain later ei th increased and adequate a.'1lounts of prolactin. n

Hel son (50) "Vie have never been able to maintai n lactation induced by pituitary extracts indefin­ ately even when increasing amounts were adI1inister­ ed." Asdell (5) wes able to prevent the normal decline in milk production in goats for only a short time by means of prolactin injecti.ons. 34

Evans (17) made similar observations with goats, but found that after a lapse of 40 days wc,;s again able to increase the yield.

Evidently prolactin i~jections induce in the ?'lcl!YlI!1ary gland a refractory state, whi ch is extremely difficult to explain, inasmuch as the hypophysis has been shown to be necessary not only for the initiation of lactation but also for its continuation. Collip et al (12) Selye et a1 (59, 71)

A phase of the lactation proble:~l1 which has hardly been touched upon is the relationship of the pancreas to the mammary glands. Markowitz et al (40, 41) report three cases in which depan­ creatized bitches failed to show maDUllary grov/th

in pregnancy or lactation following parturition1 and one case in which a depancreatized bitbh suckled two pups for a month following parturition. Chaikoff et al (10, 11) report that five out of six depancreatized bitches kept alive by special diet and insulin failed to lactate when given prolactin in much larger amounts than necessary to produce lactation in normal animals. Also one case in which a depancreatized bitch showed neither 35

growth nor secretory activity in the mammary glands when she becatne 9regnant 3 months after pancreatect- amy. These experiments seem to point to the necessity of the pancreas for lactation. but no fnrther work has been done to prove or disprove this finding. So far, only a few practical applications have been made with the lactation stimulating hormone. Catchpole et al (9) has produced lact- ation in virgin heifer~, Evans (17) has done the

sa.'TIe with virgin goats. Asdell (5', j was able to prevent the normal decline of milk production in goats for a short time. The only work that has been done on hll:;nan subjects was by I(urzook et al (35) A series of 37 maternit:/ cases, most of which showed an inadequate milk supply on the 5th. or 6th. day after parturition, and in the clinical opinion of the obste-trical staff would not im- prove in their supply, were given 50 to 200 units of prolactin made as described by Riddle (56) in

~ngle or repeated doses. Most of the cases showed a gain of from 50 to 400 gm. of milk per day. The fa.ilures were easily accounted for on the 36

basis of insufficient tissue; injections given too soon following delivery; or subjects wh1 ch were already producing the maximurn amount. The provisional dos"ge as shown by their findings is 150 units followed by 100 units in from 12 to 24 hours. 37

CONCllUSIONS l'he marm1JO;j ry gland develops its duct system under the influence of the female sex hormone, theelin or oestrin. A part of this development may be accomplished before or during ?uberty. In some animals slight lobule formation may occur also as the result of oestrin stimulation at or following puberty. The completion of the duct system, and the lobule formation during preg­ nancy is due to increased runounts of oestrin secreted by the placenta, and also in some animals supplemented by the secretion of progestin from the corpus luteum. Prolactin, the hormone secreted by the anterior pituitary which is necessary for the initiation and continuation of lactation, is prevented from forming or prevented from acting by the oeEltrin, but on removing the placenta the oestrin level of the blood falls, and lactation occurs, to continue for a variable length of time if the breast is emptied, but stops if it is not, either because the distention causes involution or because the lack of stim­ ulation of the nip)les fails to stimulate reflexly the release of prolactin. 38

Injections of prolactin cause a re­ fractory state to be created in the gland against the action of prolactin. The pancreas may be necessary for the development and functioning of the mamma.ry gla.nd. 39

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