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Effect of Exogenous Luteinizing Hormone and Estrogen on the Corpora Lutea of the Hypofhysectomized Rabbit

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Effect of Exogenous Luteinizing Hormone and Estrogen on the Corpora Lutea of the Hypofhysectomized Rabbit THE EFFECT OF EXOGENOUS LUTEINIZING HORMONE AND ESTROGEN ON THE CORPORA LUTEA OF THE HYPOFHYSECTOMIZED RABBIT by DON RICHARD WARREN B.S., Kansas State University, 1964 A MASTER'S THESIS submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE Department of Zoology KANSAS STATE UNIVERSITY Manhattan, Kansas 1967 Major Professor: f 3 TABLE OF CONTENTS INTRODUCTION 1 LITERATURE REVIEW 2 MATERIALS AND METHODS 6 RESULTS 10 DISCUSSION 14 CONCLUSIONS 17 ACKNOWLEDGEMENTS 18 BIBLIOGRAPHY 19 , INTRODUCTION The ovary has two responsibilities in the intact normally functioning animal: (1) the production of follicles with fertilizable ova, (2) the production of steroids for normal physiology of the uterus and mammary tissue and feedback mechanisms to the pituitary via the hypothalmus. A malfunction results in abberation of the reproduc- tive cycle and associated behavorial phenomenon. The graafian follicle ovulates as a result of prolonged action of follicle stimulating hormone (FSH) and 10-12 hours after a surge of release of luteinizing hormone (LH) from the anterior pituitary (Hilliard et al. , 1964) which, in the rabbit, is a result of the copulatory stimulus. This stimulus sends impulses to the hypothal- amus which releases a luteinizing hormone releasing factor (LRF) into the portal circulation which in turn causes the anterior pituitary to release LH (Sawyer, 1959). Estrogen being produced in the graafian follicle also affects directly the anterior pituitary and the hypothalamus to activate release of LH into the circulation where it is reflected in elevated plasma ovarian ascorbic acid depletion (Kanematsu and Sawyer, 1964). Hypophysectoray , involving the complete removal of the pituitary gland, is a useful tool in neuroendocrinological research and therapy. By this technique pituitary factors that control ovarian function are removed thus allowing evaluation of known levels of hormone replacement therapy. The present experiment was designed to determine the effects of (1) hypophysectomy (2) exogenous LH treatment, and (3) exogenous estrogen alone and combined with LH, for elucidation of the pituitary role in luteal maintenance and regression. 5. 2 LITERATURE REVIEW Nalbandov (1961) suggested that the action of LH on the graafian follicle is that of lysing the papillary region, possibly accompanied by endosmosis resulting from rapid depolymerization of antral mucopolysaccharides by hyaluronidase (Zachariae, 1957), resulting in ovulation. The drastic release in pressure following ovulation allows for a slight contraction of the theca externa effecting increase of the folds of the granulosa. Hyperplasia and hypertrophy of the granulosa and theca interna results in cells filling the antral cavity while the theca externa gives rise to no specialized cells but serve only to encapsulate the forming and formed corpus luteum (CL) . It consists of fibrous connective tissue vascularized with arterioles and venules. The granulosa cells become luteinized forming the blossom cells of the mature CL. The theca interna cells, closely associated with the blossom cells, are the companion cells of the formed CL (Gier and Marion, unpublished). These LH initiated postovulatory changes result in the glandular corpus luteum which, under proper stimulation, secretes progesterone for the maintenance of pregnancy or the luteal phase of the cycle. Pro- gesterone causes proliferation of the uterine glands, in an estrogen primed uterus, thus providing a method of assay for the relative amount of progesterone (McPhail, 1934) . Progesterone also has a feedback mechanism that supresses pituitary gonado- trophins (Sawyer and Everett, 1959) possibly by a hypothalamic releasing factor inhibition (Sawyer and Kawakami, 1961; Smith and White, 1931). Fee and Parkes (1929) and Smith and White (1931) showed that normal ovulation would not occur if the rabbit was hypophysectomized within one hour after copulation. Hypophysectomy later than one hour after copulation had no inhibitory effect, although subsequent development of the corpora lutea appeared to be abnormal (Fee and Parkes, 1929) The corpora . lutea developed normally for two days but no further and were regressed by day 8. Spies et al. (1966) showed that the blossom cell count in the pseudopregnant rabbit reached its maximum by day 8 and then persisted until day 16 at which time it rapidly decreased. Rennie et al„ (1964) and Kilpatrick et alo (1964) showed the pituitary to be necessary through pregnancy and pseudopregnancy for normal maintenance of the CL in rabbits and that replacement therapy with prolactin did not prevent luteal atrophy as it does in the rat. A drop in pituitary LH of rabbits Immediately after mating was reported by Hill (1934) . He speculated that this drop represents aftereffects of an increased LH secretion. He further showed that the ovulating potency of the pituitary increased rapidly on day 3 and began to decline on day 10 and interpreted this rise to indicate a decreased rate of release of LH from the pituitary. Presumably a gonadotrophic complex was involved in the assay rather than just LH« Furthermore, actual levels of pituitary gonadotropin have been positively associated with plasma levels which increase concurrently with ovarian progestin (Hilliard et al. , 1964). These results imply that the developing corpus luteum requires a luteotrophin for normal development, and that to remain functional, persistent luteotrophic subr stances must be present. A luteotrophin is any substance which directly or indirectly maintains a functioning corpus luteum. A luteolysin on the contrary causes breakdown or lack of function of the corpus luteum. Both types of response have been reported with LH in the rabbit (Kilpatrick et al.,1964; Stormshak and Casida, 1964; Spies et al., 1966). The luteotrophic activity of LH is favored by Kilpatrick et al. (1964) in that they consider that LH acts indirectly on the corpus luteum effecting the interstitial tissue to secrete estrogen (Everett, 1961) which in turn maintains the functional corpus luteum. The ability of estrogen to counteract the luteolytic effect of LH would support this hypothesis (Spies et al, , 1966). Stormshak and Casida (1964) and Spies et al, (1966) found that the ovary was unresponsive to human chorionic gonado- trophin (HCG) or LH prior to day 5 and that LH or HCG would not regress the original set of CL until after day 5. The first set of CL was maintained until the second set, which was formed after day 5, regressed. o . Gurya and Greenwald (1964) showed a mobilization of lipid droplets in the estrual rabbit ovary which were thought to be steroid precursors, two hours after injection of HCG. These droplets disappeared when ovulation had taken place, 10-11 hours after injection of HCG, and by 3 days after ovulation the interstitial tissue was again laden with lipid droplets. Mobilization of these lipids as precursors of preovulatory progestin may well explain the unresponsive state of the ovary just prior to and immediately after ovulation (Hilliard et al„ , 1964). Within a few days after ovulation, basal progestin secretion gradually increases and ovarian responsiveness to exogenous LH appears to be more consistent (Endroczi and Hilliard, 1965) , This lack of proges- terone secretion after ovulation may in some way be coupled with the inability of LH to be luteolytic until day 5 of pseudopregnancy Stormshak and Casida (1964) found FSH on day 9 to cause reduced weight of the CL and the same effect was obtained with relatively small doses of HCG or LHo Contami- nation of the FSH with LH is inevitable and could explain the FSH luteolytic effect. Spies et al„ (1966) noted similarly a reduced blossom cell count, indicative of luteal involution following FSH injection on day 7. LH appeared to be the gonadotrophin which most readily caused reduction in weight and decreased luteal cell counts. Stormshak and Casida (1964) hypothesized that stages of growth of a CL to maturity appears to be paralleled by an increasing susceptibility to the regressive action of LH. If LH does cause regression of CL in normal pseudopregnant rabbits, then it is not released in sufficient quantities to do so until late pseudopregnancy. Luteal function in pregnancy may be controlled by estrogen, and a decrease in the production of estrogen may be followed by regression of luteal activity and partur- ition. In the intact pseudopregnant and pregnant rabbit, continual estrogen will maintain the corpus luteum (Allen and Heckel, 1936). Allen (1937), and Robson (1937, 1939) showed that estrogen would maintain the corpora lutea of the hypophysectomized rabbit sufficiently to maintain pregnancy (Robson, 1940) 5 Microcrystals of estrogen Implanted into the corpus lutetim maintains parts of the corpus luteum, establishing the concept of local effect of estrogen (Hammond and Robson, 1951) . Local luteal cell maintenance was also effected in the hypophysecto- mized rabbit with a corpus luteiom graft in the mammary tissue (Hammond, J. Jr., 1952). Spies et al„ (1966) reported localized luteal regression of corpora lutea of the same age following LH and FSH treatmentc Westman (1934) showed by isolating the CL from interstitial tissue that the luteal tissue regressed but could be maintained with exogenous estrogen. Creep (1941) indicated that corpus luteum-uterus relationship was not mediated through the pituitary gland „ He reported that corpora lutea, in both intact and hypophysectomized pregnant animals, hysterectomized in the latter half of
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