Graduate Thesis Or Dissertation
 

Pituitary and uterine control of ovarian function in the gilt and ewe

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  • The role of the pituitary gland and uterus in regulating ovarian function in the estradiol-treated gilt and ewe was investigated in two experiments. Pituitary gonadotropin content, ovarian follicular development and corpus luteum function were studied following daily intramuscular injection of seven gilts with 7 mg of 17β-estradiol from day 11 through day 16 of the estrous cycle (first day of estrus = day one of the cycle). Seven control gilts were injected with corn oil for the same duration. Control and treated gilts were autopsied on day 17 of the cycle. Exogenous estradiol caused an increase in pituitary FSH and LH activity (P < .01, for each gonadotropin) and increased anterior pituitary dry weight (P < .05). Treatment of gilts with estradiol inhibited ovarian follicular growth beyond 5 mm in diameter, reduced the number of follicles ≥ 3 mm in diameter (P < .01) and depressed follicular fluid weight (P < .01). Injection of estradiol into gilts was without effect on luteal weight, but increased luteal progesterone content and concentration (P < .01, for each characteristic). Effect of time of hysterectomy on luteal characteristics of estradioltreated ewes and the effect of estradiol on uterine protein synthesis in these ewes were investigated. Fifteen ewes were assigned randomly in equal numbers to three treatment groups and were injected intramuscularly with 750 μg of 17β-estradiol on each of days 10 and 11 of the cycle (first day of estrus = day zero of the cycle). Ewes were hysterectomized as follows: group 1, immediately before the first injection (zero hour); group 2, 24 hours following the first injection and prior to the second injection, and group 3, 48 hours following the first injection. In addition, two ewes were injected with vehicle on each of days 10 and 11 of the cycle and hysterectomized 24 and 48 hours following the first injection. All ewes were autopsied on day 15 of the cycle. Following hysterectomy, samples of endometrium from the uterine horn ipsilateral to the ovary containing the corpus luteum from one ewe in each group and the two control ewes were incubated for two hours at 37°C under 95% 0₂-5% CO₂ in Eagle's HeLa medium containing 7 μCi of uniformly labelled L-leucine-¹⁴C. The tissue was homogenized in 0.05% Na₂EDTA, centrifuged and the supernatant subjected to polyacrylamide gel electrophoresis, Sephadex column chromatography and dialysis to determine the extent of incorporation of leucine into newly synthesized endometrial protein. Removal of the uterus at 24 hours following injection of ewes with estradiol blocked corpus luteum regression whereas hysterectomy at 48 hours failed to prevent estradiol-induced luteal regression (P < .05). Time of hysterectomy was without effect on luteal progesterone content of estradiol-treated ewes. Luteal progesterone concentration of ewes hysterectomized 48 hours following the initial injection of estradiol was greater (P < .05) than that of ewes hysterectomized at 24 hours, but did not differ from the luteal progesterone concentration of ewes hysterectomized prior to estradiol treatment (zero hour). Luteal progesterone concentration of ewes hysterectomized 24 hours after the initial injection of estradiol did not differ from that of ewes hysterectomized prior to estradiol treatment. Incorporation of labelled leucine into endometrial protein was maximal at 24 hours and was reduced at 48 hours following estradiol injection. Incorporation of leucine into certain endometrial proteins tended to increase progressively with time following estradiol injection, whereas incorporation of this amino acid into some other endometrial proteins tended to decrease with time. Results of Sephadex column chromatography and dialysis indicate that labelled leucine was actually incorporated into uterine protein. Data from the present experiment suggest that there may be a relationship between estrogen-induced uterine protein synthesis and luteal regression in the ewe.
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