Contraception-A Look Forward, Part III: Inhibin J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from And Brain-Enhanced Estrogen Delivery

Robert]. Wool/ey, M.D.

Abstract: The final installment of this review examines two contraceptive methods, inhibin and brain-enhanced estrogen delivery, which are radically ditl'erent from any currently available. Inhibin is a gonadal honnone that specifically inhibits pituitary production of follicle-stimulating honnone. Before it was finally isolated in 1985, inhibin was expected to be an ideal contraceptive. Recent research, however, has shown that the inhibin honnonal system is unexpectedly complex, and hopes for clinical use of inhibin must be suspended for the present. Although oral contraception is one of the most effective methods ever devised, use is limited by adverse effects of estrogen (or fears of such effects). Asystem known as brain-enhanced estrogen delivery specifically delivers estrogen to the brain, including the hypothalamus, there inducing suppression of the gonadotropin-releasing hormone. It has been described and tested in animals, and its successful development could replace current oral contraceptives and extend their availability to many more women. o Am Board Fam Pratt 1991; 4:159-66.)

Inhibin inhibition of FSH. Inhibin, produced in the male The earliest clue to the existence of the honnone Senoli cells and female granulosa cells, was be­ now known as inhibin was the 1923 observation lieved to be the mechanism responsible. (The that radiation damage to the germinal epithelium inhibition of FSH production was, in fact, the of rat testes resulted in hypertrophy of specific primary means of assaying for the presence or cells of the anterior pituitary, much as would cas­ purity of inhibin.) tration; this hypertrophy was postulated to be due Based on this model, projections were made that to loss of some unknown testicular secretion. In inhibin, once isolated, would make an ideal con­ the early 193 Os, a watery extract of bull testes was traceptive drug. Given to men, it would cunail shown to reverse this pituitary cellular hypertro­ spennatogenesis by FSH deprivation without de­ http://www.jabfm.org/ phy with no apparent effect on the sex organs. pression of LH, testosterone, or libido. In women, "Inhibin" was the name given the unidentified it would prevent recruitment and development of factor responsible for these changes. Its character ovarian follicles, processes that require FSH. Such remained unknown for another 50 years. 1 optimistic forecasts continued to be made as late as During this period, the main features of the 1986.2 They would prove to be premature. luteinizing honnone, follicle-stimulating hor­ Inhibin was finally purified and its amino acid mone, and gonadotropin-releasing honnone sequence deduced in 1985. (The progression of on 1 October 2021 by guest. Protected copyright. (LH-FSH-GnRH) system were elucidated. this work has been reviewed in detai1.1,3,4) Jock Among other things, release of LH and FSH was Findlay (W'orld Health Organization Special found at some periods of the life cycle to be under Programme in Human Reproduction) soon separate control. This action could not be attrib­ thereafter reviewed what was known and not uted to GnRH, which consistently stimulates re­ known about inhibin. S He identified, among oth­ lease of both honnones. The explanation seemed ers, the following defects in our knowledge and to be that LH could be released without FSH, not the unanswered questions about inhibin's ability by selective stimulation of LH, but by selective to function as a contraceptive agent:

From the University of Minnesota, Department of Family In men: Practice and Community Health, St.}oseph's Hospital Residency Program, St. Paul. Address reprint requests to Robert}. Woolley, 1. The degree to which spennatogenesis de­ M.D., cio Bethesda Family Physicians, 590 Park Street, Suite 310, St. Paul, MN 55103. pends upon FSH in nonnal men is unknown;

Contraception 159 at least oligospermic levels can be maintained could contribute to the genesis of polycystic ovar­ J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from by LH alone. ian disease. l 2. If FSH is necessary for spermatogenesis, will As though these challenges were not enough, inhibin suppress its production sufficiently? subsequent research has shown the model of a 3. IT oligospermia can, in fact, be induced by simple inhibin-FSH feedback loop to be woefully inhibin, how is the fertilizing capacity of the inadequate. remaining sperm affected? Inhibin is found in two forms, A and B, each 4. Because high doses of inhibin also suppress consisting of an (X subunit and a ~ subunit. The (X LH production, will testosterone supplemen­ subunit has only one known form, an 18- tation be required for treated men? kilodalton (kD) polypeptide. Two known forms of the ~ subunit are the similar but distinct poly­ In women: peptides of 14-kD molecular weight, known as ~ A

and ~B' Inhibin A is a climer of (X and ~A' joined 1. The effects of pure inhibin (free of other by disulfide bonds; inhibin B is formed by (X and biologically active, gonadally derived agents) ~B (Figure 1). Inhibins A and B appear to have on in vivo FSH production and ovulation, similar activities in vitro, and the physiological luteal function, and cycle length are un­ purpose of the existence of separate forms, if any, known. is not known. It has been demonstrated, however, 2. In theory, too little FSH suppression would that these forms of inhibin are produced in lead to luteal phase deficiency and short cy­ several extra gonadal sites (such as bone marrow, cles; too much suppression could cause amen­ placenta, and pituitary and adrenal glands), as well orrhea, LH suppression, and the problems of as in the ovary and testis, and that RNA expres­ unopposed estrogen. Can a correct dosage sion of the inhibin subunits varies among differ­ range be found? ent tissues, implying that the ratios of the dimers 3. What will be the clinical consequences of the may cause tissue-specific differences in inhibin known tendency of FSH production to re­ function.6 bound to abnormally high levels after ceasing In 1986, it was reported that climers of the ~ suppression by inhibin? subunits, with no (X component, also possessed biological activity, but their effects oppose those of For both sexes: the inhibins.7-9 The ~A-~A homo climer and the

~A-~B heterodimer are potent stimulators of http://www.jabfm.org/ 1. Will long-term use of inhibin, a glycoprotein, pituitary FSH synthesis and secretion in vitro. induce antibody response? (This could theo­ "Activin" is produced by the Leydig cells in men; retically result in eventual hyperfecundity the ovarian site of synthesis has yet to be identi­ after inhibin treatment ends, because of inac­ fied. lo Whether activin is actually circulated out­ tivation of endogenous inhibin.) side the gonads in vivo is unknown. The two

2. Can the cost be made competitive with that of on 1 October 2021 by guest. Protected copyright. other forms of contraception? FSH Suppressor 3. Inhibin is known to demonstrate some ge­ netic and structural homology with human inhibin A inhibin B 1:::::::::::::::::::::.::::::,1 transforming growth factor-~ (TGF~). Follistatin TGF~ can either promote or inhibit cell growth, depending on the presence of other growth factors, and is found in some types of neoplastic tissues. Can such potential long­ term effects confidently be excluded on the TGFf3 activin A activin AB activin(?) basis of standard clinical trials? FSH releaser

It has also been suggested that an increase in Figure 1. Gonadal protein honnones modulating the the ratio of circulating LH to FSH (an effect that secretion ofFSH. Redrawn and used with pennission would be expected after inhibin administration) fromYing.4

160 JABFP May-June 1991 Vol. 4 No.3 fonns are being called activin A and activin A-B, inhibin and activin appear to influence FSH pro­ J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from . respectively.ll (The existence of a f3 B-f3B homo­ duction at the level of protein synthesis, rather dimeric form would produce a logical than the level of hormonal release, as with completeness but has not yet been verified) (Fig­ GnRH.) A hypothalamic-releasing hormone ures 1-3). more specific for FSH than for LH has long been Although both GnRH and activin can provoke postulated, with some supporting experimental release of FSH, activin differs in having no effect evidence,3 and has even been provisionally named on LH, no interference from synthetic GnRH by its proponents "follicle-stimulating hormone analogues, and a slower onset of action. (Both releasing hormone" (FSHRH)j activin appears not to be the same as this supposed fuctor. 7 The model of the hypothalamic-pituitary-go­ nadal axis was further complicated the year after the djscovery of the activins by the announcemen t of follistatin. 12,13 Follistatin is a protein derived from follicular flilld. (Actually, it is two somewhat different proteinsj the molecular weight of one is 32 kD, the other is 35 kD.) It specifically sup­ presses the secretion of FSH by pituitary cells in vitro but is not homologous with inhlbin or acti­ Estradiol EB Estradiol vin (Figures 2 and 3). Its action is distinguished Inhibin Activin Progesterone Progesterone Follistatin FSH from that of inhlbin by lower potency (on an FSH Et> e- eqrumolar basis) and by suppression of FSH re­ LH LH EB .J ... Follicular lease rather than FSH synthesis. The effects of 'vI'development ,.,.,- follistatin and inhlbin are additive, and antibodies "\ raised against one are not cross-reactive with the l~=I.="-0; = tI ;; 1_ '~ ,J other. As with the activins, whether follistatin is released outside the gonads in vivo is not yet $ ~"'lj known. Surprises about this endocrinologic axis con­ JC~-~-""" tinue to be announced at a perplexing rate. The ~ --.."J'I- Estradiol Et> ~ Progesterone following are samples of recent discoveries: http://www.jabfm.org/ ~~---­ Female ~:W- tissues 1. Inhlbin is secreted by selected areas of a Corpus luteum rat brain, including neurons that termi- on 1 October 2021 by guest. Protected copyright. Figure 2. (a) Summary ofhonnonal control of or.uian function. The hypothalamus produces GnRH (LRF), which acts on the pituitary cells to secrete FSH and LB. A secretion of FSH, together with tonic LB, stimulates the follicular development. The developed follicles secrete estradiol, progesterone, inhibins, activins, and follistatins. Estradiol and progesterone, at different concentrations or ratios, either positively or negatively feed back to the hypothalamic hypophyseal axis in regulating the secretion of FSH and IJI. lnhlbins and follistatins specifically suppress, whereas activin and TGFf3 enhance the secretion of FSH by the pituitary. (b) Schematic representation of intragonadal function of inhibins, activins, TGFf3, and follistatin. Redrawn and used with pennission from Ylng, 1988.4

Contraception 161 5. Activin can elicit oxytocin secretion, and anti­ bodies to inhibin (which probably cross-react J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from with activin) attenuate oxytocin secretion and lactation. 14 6. Activin has been confirmed to stimulate erythropoiesis in laboratory animals, as well as tissue cultures. IS 7. Both inhibin and activin may be mediators of the immune response through action on thy­ mocytes.19 Estradiol Inhibin Follistatin The rapid sequence of discovery of activin and LH Activin Germinal follistatin obviously raises the possibility of other cell factors regulating FSH control of the gonads. In addition, the role of inhibin itself in normal human physiology is essentially unknown. The hopes of rapid development of inhibin as an anti­ fertility drug were obviously premature. The rev­ elations of recent years have, if nothing else, reminded us of our ignorance of the complex . workings of biological systems. Figure 3. Summaryofhonnonal control of testicular Artificial regulation of FSH may eventually function. GnRH (LRF) secreted by hypothalamic prove to be a feasible means of contraception for neurons transported by axons to hypophyseal portal men, women, or both, but even speculation on vessels to the anterior pituitary to release LH and FSH. how this can be achieved must be postponed for LH acts on Leydig cells to secrete testosterone, which several years. stimulates the gennina1 cells for spermatogenesis, whereas FSH stimulates gonadal protein production by Brain-Enhanced Estrogen Delivery Set10li cells (inbibin, activins, or follistatin). Testicular The development of combination oral contracep­ steroids negatively feed back to hypothalamic­ tives was undoubtedly the greatest achievement in bypopbyseal axis for LRF-FSH or LH secretion. Inhibin

reversible contraception since the elucidation of http://www.jabfm.org/ and follistatin specifically suppress, while activin enhances FSH release by the pituitary. Inhibin the fertile phase of the menstrual cycle in the 1930s. After more than 25 years of general use, increases, but activin and TGF~ (a protein widely distributed in the body) decrease testosterone pro­ "the pill" remains one of the most popular, ef­ duction by Leydig ceUs. Modified and redrawn from fective, and safe forms of birth control in the YlDg, 1988.4 world. The primary mechanism of oral contraceptives on 1 October 2021 by guest. Protected copyright. is the inhibition of LH and FSH release. To­ nate in the GnRH-producing areas of the gether these prevent ovarian follicular develop­ hypothalamus. 14 ment and ovulation. This suppression is due to 2. In men, inhibin production can apparently be the effects of the estrogenic and progestogenic stimulated directly by FSH and also indirectly components on both the anterior hypophysis and by LHj this latter is a phenomenon not seen the hypothalamus. Secondary antifertility effects 1S in any animal species. are those exerted by the hormones directly on the 3. Inhibin levels are elevated in the presence of female reproductive organs, including changes in hydatidiform moles and may prove to be a endometrial proliferation, uterine tube ciliary clinically useful marker of postevacuation motility, and cervical mucus production and con­ 16 persistent trophoblastic disease. sistency. 4. Granulosa cell tumors secrete elevated levels Despite the general safety and popularity of of inhibin, and inhibin has been suggested as oral contraceptives, their use is prevented in or a serum tumor markerP avoided or discontinued by many women as a

162 JABFP May-June 1991 Vol. 4 No.3

1 charged result of the many other effects of estrogen. Risk native is increased for thrombotic events, hypertension, carrier 8 J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from condenlatlon benign liver tumors, and gallbladder disease, and 1 + Ez with ..tredid the issue of breast cancer seems never to be re­ solved. Serum triglycerides can be elevated. Sub­ jective side effects include weight gain, depres­ ch.mic.. r.duC1Kwi sion, nausea, and headache. Drug interactions uncharg.d carrier- have been reported with antibiotics, barbiturates, astradkl' 0-E complex 2 anticonvulsants, antidepressants, theophylline, and vitamins. All of these adverse effects are due largely to the peripheral actions of the estrogen in rr======:;~ active oral contraceptives. Oral contraceptive use could tran.port presumably increase significantly if these effects were reduced or eliminated by delivering the hor­ Q-EZ rapid enzymatic mone selectively to the pituitary or hypothalamus blood­ oxidation ~ri.ph'''11 brl'" "'Uu' and avoiding its distribution to other tissues. barrier G)-EZ slow membranH .ntymadc: A chemical delivery system (CDS) to accom­ cltlvag. plish this goal is being developed by a group at the 1 University of Florida and two proprietary inter­ ests, Gynex (Deerfield, IL) and Pharmatec (Al­ cannot hypothal- achua, FL). pass ernie ba" .., reee r The brain-enhanced delivery of estrogen is a slow migration wHO circulation ,.pid migration specific application of general pharmacologic into cirewadon agents developed to overcome the difficulty of drug penetration of the blood-brain barrier.2o The principal component of the blood-brain bar­ rier is a network of tight junctions between capil­ lary endothelial cells, which force blood-borne substances to migrate through, rather than be­ Figure 4. Simplified schematic representation of the tween, these cells, either to enter or to exit the synthesis and distribution of a brain-enhanced brain parenchyma. This passage is enhanced by chemical deUvery system for estrogen. Modified from http://www.jabfm.org/ lipophilia (to traverse the luminal and abluminal Brewster ME, Estes KS, Bodor N.23 membranes) and by the ability to use any of a number of specific carrier systems present in cause the 17 -esterification prevents binding with the endothelial cells. Many drugs do not have estrogen receptors. Pharmatec's developmental these properties and are excluded from central designation for the complex is PR-63. nervous system entry. In the case of the steroid Intravenous administration of this compound on 1 October 2021 by guest. Protected copyright. hormones, the problem is slightly different; their in animals results in rapid tissue distribution be­ lipophilia allows easy passage into the brain, cause of ease of membrane passage. In peripheral but an equally easy escape from it, thus necessitat­ tissues, the enzymatically labile dihydropyridine ing constant serum levels to maintain constant carrier is rapidly oxidized back to its more stable brain levels. quaternary salt form, rendering it hydrophilic and Bodor, et aJ.21 reported successful testing of a subject to renal elimination. (It is believed that brain-selective estrogen delivery system. Estra­ oxidation is due to the ubiquitous NADH-dehy­ diol is first condensed with trigonelline (1- drogenases.)20 In the brain, similar transmem­ methylnicotinic acid, a natural metabolite of brane passage and oxidation of the carrier moiety nicotinic acid [niacin]), then quaternized and re­ to its polar form occur, but the blood-brain bar­ duced to remove the ionic charge. The product is rier then prevents outward migration of the now­ a highly lipophilic chemical delivery system, an ionic compound. The carrier-estrogen complex estradiol esterified with a carrier. This hybrid is, in essence, trapped in the central nervous sys­ molecule has low inherent estrogenic activity be- tem by its conversion to a polar form. Slow hy-

Contraception 163 drolysis of the estrogen-carrier ester bond then rats 16 days after estradiol-carrier treatment, sug­ J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from results in gradual release of free estradiol, which gesting that gradual release of the active estradiol binds to the estrogen receptors in the hypothala­ from its carrier suppresses release of GnRH from mus in the usual manner, thus suppressing the the parvicellular neurons of the hypothalamus. release of GnRH and, consequently, LH and They also note that, because they did not see a late FSH (Figure 4). LH surge, the site of action of the estradiol deliv­ As well as being elegant in theory, this chemical ery system is more likely to be the hypothalamus delivery system has been reported effective in than the pituitary; continual estrogen stimulation laboratory rats. In vivo half-life values of the tis­ of the pituitary changes its negative-feedback sue-oxidized compound are 46 minutes in the loop to a positive-feedback loop (as in the late liver, 5.5 hours in the lung, 8 hours in the kidney, follicular phase of the menstrual cycle) and should and 23 hours in the brain. Detectable levels of have produced such a surge if the pituitary were estradiol were found in the brain of these rats, but the primary repository of the carrier estradiol. not the blood, implying release of estradiol from (The anterior pituitary is outside the blood-brain the trapped carrier molecule.21 barrier and would be expected to demonstrate Evidence for the predicted biological activity rapid elimination of administered estrogen car­ of the carrier-released estrogen was found in rier, just as do peripheral tissues.) oophorectomized rats. A single large injection (or A movement from laboratory to clinical studies repeated smaller doses) of PR-63 produced is underway on several fronts. First, unpublished dose-dependent reduction in serum LH.22 Fur­ animal studies on the feasibility of oral adminis­ thermore, a therapeutic range was established tration have shown no gastrointestinal oxidation that allows suppression of LH without increasing of the dihydropyridine carrier, which would pre­ serum estradiol or prolactin levels. vent its access to the central nervous system and Similar results have been obtained using the defeat the purpose of the CDS, but the studies same delivery system to carry ethinyl estradiol, a have shown some degree of cleavage of the ester potent synthetic estrogen commonly used in oral bond by which it holds the estradiol. For this contraceptives.23 Ethinyl estradiol and estradiol reason, sublingual tablets will probably be the carrier systems were equally effective at long­ form of administration ultimately developed term (18 days) suppression of LH. The ethinyl (Kerry S. Estes, Ph.D., personal communication,

estradiol system was shown to have the same de­ 13 February 1990). Second, the first human trials http://www.jabfm.org/ sirable properties as the estradiol system, namely, of the CDS have already begun. Intravenous ad­ short peripheral elimination half-life and long ministration of PR-63 to 10 postmenopausal brain half-life. (Because the ethinyl estradiol sys­ women demonstrated sustained, dose-dependent tem showed no clear advantage over that using suppression of LH release with no subjective side the natural estradiol, future research is expected effects or adverse effects on pulse, blood pressure, to focus on the latter.) or serum chemistry determination.25 Third, the on 1 October 2021 by guest. Protected copyright. Inhibition of ovulation by the estradiol chemi­ addition of a cyclodextrin complex to the formu­ cal delivery system was reported by a group at the lation has been found to extend its shelf life and University of California at San Diego.24 The increase its water and tissue solubility. 26 chemical delivery system was three times as effec­ Uses for this system other than contraception tive as an equimolar dose of free estradiol at have been proposed. The goal of estrogen treat­ lengthening the estrous cycle of rats; to double ment of prostate cancer is the suppression of the length of the cycle required only 1120th the gonadal testosterone production by artificial inhi­ molar dose of estradiol when coupled to the de­ bition of LH release. This action could presum­ livery system. Treated rats had significant delays ably be accomplished by hypothalamic suppres­ in LH surge and ovulation. Brain level elevations sion of GnRH release by PR-63, greatly reducing of estradiol persisted four to five times longer the peripheral side effects of traditional estrogen when the hormone was delivered by carrier. therapy, such as hypertension and edema.23 The These researchers also found elevated levels of vasomotor symptoms of menopause could proba­ GnRH in the hypothalamus and depressed levels bly be suppressed by PR-63,23 and relief thus in the hypothalamic-hypophyseal portal vein of provided for the many symptomatic women who

164 JABFP May-June 1991 Vol. 4 No. 3 have a contraindication to systemic estrogens. 7. Tsonis CG, Sharpe RM. Dual gonadal control of J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from The many beneficial effects of systemic estrogen follicle-stimulating hormone. Nature 1986; 321: in menopausal women, however, would be for­ 724-5. 8. Vale W, Rivier J, Vaughan J, McClintock R, feited. Finally, this system might be useful in Corrigan A, Woo W, et al. Purification and char­ treating obesity. In laboratory animals, the direct acterization of an FSH releasing protein from estrogenic stimulation of the hypothalamus pro­ porcine ovarian follicular fluid. Nature 1986; duces long-term weight loss, and these effects 321:776-9. 9. Ling N, Ymg SY, Ueno N, Shimasaki S, Esch F, have been duplicated with PR_63.27,28 Hotta M, et al. Pituitary FSH is released by a This system is still in the early testing stages. heterodimer of the ~-subunits from the two furms of Full toxicology studies need to be performed, inhibin. Nature 1986; 321:779-82. although the carrier itself appears not to be neu­ 10. Lee W, Mason A], Schwall R, Swnyi E, Mather JP. rotoxic to primates.29 Much remains to be learned Secretion of activin by interstitial cells in the testis. about the pharmacologic fate of the carrier in Science 1989; 243:396-8. different tissues, the multiple endocrinologic ef­ 11. Burger HG, Igarashi M, Baird DT, Bardin W, Chap­ pel S, de J ong F, et al. Inhibin: definition and nomen­ fects of the gradual central nervous system release clature, including related substances. Clin Endocrinol of estrogen (e.g., on FSH and progesterone), and (Oxf) 1988; 28:448-9. the need for concomitant progestin use. Con­ 12. Ying SY, Becker A, Swanson G, Tan P, Ling N, Esch ceptually, there is no obvious barrier to eventual F, et al. Follistatin specifically inhibits pituitary fulli­ success. cle stimulating hormone release in vitro. Biochem Biophys Res Commun 1987; 149:133-9. Such success should mean the ability to inhibit 13. Ueno N, Ling N, Ymg SY, Esch F, Shimasa'ki S, LH release and ovulation with much lower doses Guillemin R. Isolation and partial characterization of estrogen than are used in current oral contra­ of follistatin: a single-chain Mr 35,000 monomeric ceptives, resulting in fewer problems created by protein that inhibits the release of follicle-stimulat­ circulating and tissue-bound estrogens and pre­ ing hormone. Proc Natl Acad Sci USA 1987; sumably with less frequent dosing. Not only could 84:8282-6. 14. Sawchenko PE, Plotsky PM, Pfeiffer Sw, Cun­ this achievement supplant all current oral contra­ ningham ET Jr, Vaughn J, Rivier J, et a1. Inhibin ~ ceptives, it could greatly enlarge the number of in the central neural pathways involved in the women able to use them. control of oxytocin secretion. Nature 1988; 334: 615-7. 15. McLachlan RI, Matsumoto AM, Burger HG, de

My thanks to Anne Robin, M.D., and David K. Webb, M.D., Kretser DM, Bremner WJ. Relative roles of follicle­ http://www.jabfm.org/ for helpful hints and encouragement; to Linda Coates, Karen stimulating hormone and luteinizing hormone in the Brudvig, and the entire medical library staff at the University of control of inhibin secretion in normal men. J Clin nlinois, Urbana, for expert bibliographic assistance; and to my Invest 1988; 82:880-4. wife, Betsy, for respecting my hours in the library. 16. Yohkaichiya T, Fukaya T, Hoshiai H, Yajima A, de Kretser DM. Inhibin: a new circulating mark­ References er of hydatidifurm mole? Br Med J 1989; 298: 1. de Jong Inhibin-its nature, site of production, 1684-6.

FR. on 1 October 2021 by guest. Protected copyright. and function. OxfRev Reprod BioI 1987; 9:1-53. 17. Lappohn RE, Burger HG, Bouma J, Bangah M, 2. Sheth AR, Moodbidri SB. Potential application of Krans M, de Bruijn Hw. Inhibin as a marker fur inhibin in male and female contraception. Adv Con­ granulosa-cell tumors. N Engl J Med 1989; 321: tracept 1986; 2:131-9. 790-3. 3. Li CR, Ramasharma K. Inhibin. Annu Rev Phar­ 18. Schwall R, Schmelzer CH, Matsuyama E, Mason AJ. macol Toxico11987; 27:1-21. Multiple actions of recombinant activin-A in vivo. 4. Ymg SY. Inhibins, activins, and fullistatins: gonadal Endocrinology 1989; 125:1420-3. proteins modulating the secretion of follicle-stimu­ 19. Bremner WJ.lnhibin: from hypothesis to clinical ap­ lating hormone. Endocr Rev 1988; 9:267-93. plication. N EnglJ Med 1989; 321:826-7. 5. Findlay J. The nature of inhibin and its use in the 20. Bodor N, Brewster ME. Problems of delivery regulation of fertility and diagnosis of infertility. of drugs to the brain. Pharmacol Ther 1982; 19: Fertil Steril1986; 46:770-83. 337-86. 6. Meunier H, Rivier C, Evans RM, Vale W. Gonadal 21. Bodor N, McCornackJ, Brewster ME. Improved de~ and extragonadal expression of inhibin a, ~A. and ~B livery through biological membranes. XXll. Synthe­ subunits in various tissues predicts diverse functions. sis and distribution of brain-selective estrogen Proc Natl Acad Sci USA 1988; 85:247-51. delivery systems.lntJ Pharm 1987; 35:47-59.

Contraception 165 J Am Board Fam Pract: first published as 10.3122/jabfm.4.3.159 on 1 May 1991. Downloaded from 22. Anderson WR, Simpkins Jw. Brewster ME, Bodor 26. Brewster ME, Estes KS, Loftsson T, Perchalski R, N. Evidence for suppression of serum LH without Derendorf H, Mullersman G, et al. Improved deliv­ elevation in serum estradiol or prolactin with a ery through biological membranes. XXXL: solubili­ brain-enhanced redox delivery system for estradiol. zation and stabilization of an estradiol chemical Life Sci 1988; 42:1493-502. delivery system by modified ~-cyclodextrins. J 23. Brewster ME, Estes KS, Bodor N. Improved deliv­ Pharm Sci 1988; 77:981-5. ery through biological membranes. 32. Synthesis 27. SimpkinsJw. Anderson WR, Dawson RJr, Seth A, and biological activity of brain-targeted delivery sys­ Brewster M, Estes K, et al. Chronic weight loss in tems for various estradiol derivatives. J Med Chem lean and obese rats with a brain-enhanced chemical 1988; 31:244-9. delivery system for estradiol. Physiol Behav 1988; 24. Sarkar OK, Friedman SJ, Yen SS, Frautschy SA. 44:573-80. Chronic inhibition of hypothalamic-pituitary-ovar­ 28. Estes KS, Brewster ME, Bodor NS. A redox system for ian axis and body weight gain by brain-directed brain targeted estrogen delivery causes chronic body delivery of estradiol-17~ in female rats. Neuro­ weight decrease in rats. Life Sci 1988; 42:1077-84. endocrinology 1989; 50:204-10. 29. Brewster ME, Estes KS, Perchalski R, Bodor N. A 25. Howes J, Bodor N, Brewster M, Estes K, Eve dihydropyridine conjugate which generates high and M. A pilot study with PR-63 in postmenopausal sustained levels of the corresponding pyridinium salt volunteers [abstract]. J Clin Pharmacol 1988; in the brain does not exhibit neurotoxicity in cyn­ 28:951. omolgus monkeys. Neurosci Lett 1988; 87:277-82.

NOTICE

Cerffflcate of Added Qualifications in Geriatric Medicine http://www.jabfm.org/ Examination April 10, 1992 The next examination for the American Board of Family Practice Certificate of Added Qualifications in Geriatric Medicine will be administered on April 10, 1992. Application materials for this exam on 1 October 2021 by guest. Protected copyright. will be available July 1, 1991. ABFP Diplomates interested in partiCi­ pating in the exam should request application materials by writing to: Geriatric Medicine Examination American Board of Family Practice 2228 Young Drive Lexington, Kentucky 40505-4294

166 JABFP May-June 1991 Vol. 4 No.3