Graduate Thesis Or Dissertation
 

Some effects of estradiol on ovine luteal function

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  • Some effects of 171β-estradiol on ovine luteal function were studied in five experiments. Estradiol injected into ewes on days 11 and 12 of the estrous cycle caused luteal regression in both intact and unilaterally hysterectomized ewes indicating that the presence of one uterine horn permits estradiol to cause luteolysis comparable to the effect of this hormone in intact ewes. On the other hand, corpora lutea on the ovary adjacent to the intact uterine horn in unilaterally-hysterectomized estradiol-treated ewes were smaller in size than the glands on the opposite ovary suggesting that at least part of the luteolytic effect of estradiol may be mediated via the adjacent utero-ovarian channels. Luteinizing hormone (LH) injected into intact ewes on days 9 through 13 of the estrous cycle prevented complete luteal regression, induced by estradiol injected on days 10 and 11. Treatment of ewes with LH, however, was unable to entirely overcome the detrimental effect of injected estradiol on luteal progesterone content and concentration. Luteal weights of ewes either at laparotomy or autopsy were heavier at day 13 than at day 6 of the estrous cycle. Estradiol injected into ewes on day 4 or day 11 of the estrous cycle failed to affect the luteal weight as determined at autopsy of ewes on day 6 or 13 of the same cycle, respectively. Serum of blood samples drawn from the jugular vein of each ewe over a two day period beginning at the time estradiol was injected, was analyzed for LH by radioimmunoassay. For comparison purposes, serum of blood samples from ewes at estrus drawn over a two day period beginning at the time estrus was initially detected, was also analyzed for LH. Serum LH peaked between 4 to 20 hours after the onset of estrus ranging from 62-103 ng/ml. A peak in serum LH was observed ranging from 7.2-21.0 ng/ml, 16 to 20 hours after the injection of estradiol into ewes on day 4. The short duration of the LH peak was similar to that observed in ewes at estrus. Estradiol treatment of ewes on day 11 caused no significant changes in serum LH levels. Although LH levels fluctuated beginning about 16 hours after estradiol treatment, the highest values observed were only about twice the baseline levels. The luteotropic effect of LH released by estradiol administration at day 4 appears to protect the corpus luteum from the luteolytic effect of estradiol whereas the relatively small amount of LH release induced by estradiol on day 11 of the cycle does not seem to establish a luteotropic LH to Luteolytic estradiol ratio compatible with maintenance of the corpus luteum. Effect of estradiol on the in vitro conversion of pregnenolone-4- ¹⁴C to progesterone by luteal slices of ewes on day 6 and day 13 of the estrous cycle was studied. Luteal slices of ewes on day 6 converted more labeled pregnenolone to progesterone than luteal slices of ewes on day 13 of the cycle. Addition of estradiol to the incubation medium inhibited the conversion of labeled pregnenolone to progesterone by luteal slices at both stages of the cycle studied, particularly at the highest concentration of estradiol. It is suggested that estradiol may have acted directly or indirectly on Δ - 3β-hydroxysteroid dehydrogenase to inhibit the incorporation of labeled pregnenolone into progesterone. Increased inhibitory action of estradiol on luteal progesterone synthesis by day 13 luteal slices may be the result of a lower content of Δ⁵ -3β-hydroxysteroid dehydrogenase in day 13 luteal tissue.
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file details AkbarAbulfatahM1971.pdf 2017-08-23 Öffentlich Herunterladen