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P L Keyes

Publications and source records attributed to P L Keyes.

At least 73 records · Page 4Linked to original sources
PubMed1976

Lack of gonadotropic activity in the rabbit blastocyst prior to implantation.

Recent reports of an LH-like hormone in the rabbit preimplantation blastocyst and of elevated serum progesterone levels in the presence of unimplanted blastocysts prompted us to characterized further the biological activity of the presumed gonadotropin. Progesterone was measured by a highly specific radioimmunoassay in sera obtained from pregnant and pseudopregnant rabbits after mating (day 0) to fertile or vasectomized males. On days 3, 4, 5, and 6, which represent the preimplantation period, mean progesterone concentrations (ng/ml +/- SE) were 4.3 +/- 0.7, 5.1 +/- 0.5, 6.8 +/- 1.1, and 9.0 +/- 1.9 in 5 pseudopregnant rabbits and 4.1 +/- 0.4, 6.7 +/- 0.6, 5.9 +/- 0.9, and 7.0 +/- 0.8 in 7 pregnant rabbits. In a separate experiment, serum progesterone concentrations in 6 pseudopregnant and 8 pregnant rabbits were 10.1 +/- 0.7 ng/ml and 13.7 +/- 1.1 (P less than 0.02), respectively on days 11-12. Thus, serum progesterone concentrations were not different in pregnant and pseudopregnant rabbits before the time of implantation (day 7), but were higher in pregnant rabbits after implantation. Blastocysts obtained on day 6 and incubated with a cell suspension of immature rat ovaries failed to stimulate the accumulation of progesterone in medium, in contrast to hCG, which was active even in the presence of blastocysts. Day-6 blastocysts also failed to stimulate the accumulation of testosterone from decapsulated rat testes and of progesterone from rabbit ovarian tissues in vitro. A gonadotropic effect of the conceptus can be observed in the rabbit within 4 to 5 days after implantation. However, we find no evidence for the existence of an LH-like hormone in the preimplantation blastocyst which stimulates the rabbit ovary to secrete progesterone.

Animals↗
PubMed1976

Synthesis of 17beta-estradiol by isolated ovarian tissues of the pregnant rat: aromatization in the corpus luteum.

Corpora lutea from pregnant rats were incubated to determine their ability to produce 17beta-estradiol and to aromatize testosterone in vitro. Corpora lutea and non-luteal ovarian tissues were removed from rats on days 7, 15, and 22 of pregnancy, and these tissues were immediately frozen or incubated separately in medium 199 at 37 C in an atmosphere of 95% O2-5% CO2 for 4 h. 17Beta-Estradiol in tissue and medium were quantified by a highly specific radioimmunoassay. The estradiol content ivnariably increased in non-luteal tissues during incubation, while it decreased or remained the same in incubated corpora lutea. The synthesis in non-luteal tissues, which was 18 to 400-fold greter. The incubation of corpora lutea (5 to 25 mg of tissue) with testosterone (200 ng) on days 7, 15, and 22 of pregnancy resulted in a mean accumulation of 17beta-estradiol in medium of 2.5 x 103 pg/mg tissue, compared with a mean value of 6 pg/mg for luteal tissue removed from the same ovaries and incubated without testosterone. The incubation of corpora lutea from 15-day pregnant rats with (7alpha-3H)-testosterone resulted in 15% conversion to presumptive (7alpha-3H)17beta-estradiol, which was isolated identically to estradiol isolated for radioimmunoassay. Recrystallization to constant specific activity revealed a high degree of radiochemical purity (75%) of the isolated (3H)estradiol. Rat diaphragm muscle and rabbit corpora lutea did not aromatize testosterone to 17beta-estradiol in amounts detectable by radioirpora lutea in vitro is virtually diol by non-luteal ovarian tissues. However,the corpora lutea show a striking capacity to aromatize testosterone, which might explain the high estradiol content of the rat corpora lutea during pregnancy. The physiological significance of this aromatizing system and of 17beta-estradiol in the corpus luteum is unknown but may be related to the luteotropic action of estradiol in the pregnant rat.

Animals↗
PubMed1975

Premature regression of corpora lutea in pseudopregnant rabbits following the removal of polydimethylsiloxane capsules containing 17 beta-estradiol.

17-beta-Estradiol, which is luteotropic in rabbits, was administered during pseudopregnancy via polydimethylsiloxane (Silastic) implants to determine the effects on serum progesterone concentrations. Implants which released estradiol at a rate of approximately 2 mug/day were place beneath the skin the day after sterile mating and ovulation (day 0). Blood (3 ml) was obtained from the marginal ear vein on days 3, 6, 9, 10, 11 and 12. Serum estradiol levels, determined by radioimmunoassay, were 2- to 3-fold higher in estradiol-treated rabbits (11.7 plus or minus 1.2 pg/ml) than in untreated pseudopregnant controls (5.9 plus or minus 1.4 pg/ml). Weights of corpora lutea in treated and control rabbits were not different at the conclusion of the experiment on day 12. Serum progesterone concentrations, also determined by radioimmunoassay, were not significantly different between treated and control animals. However, when estradiol implants were removed from other rabbits on day 10, a rapid decline in serum progesterone occurred, from 14.0 plus or minus 2.4 to 2.6 plus or minus 0.8 ng/ml 24 h later. By comparison, serum progesterone concentrations in rabbits with estradiol implants left in place and in untreated rabbits on day 12 were similar (similar to 12 ng/ml). The premature decline in serum progesterone was accompanied by a decrease in the wet weight of corpora lutea. Other experiments revealed: 1) a precipitous fall in serum estradiol to basal values within 2 h after estradiol implants were removed, preceding the decline in serum progesterone by approximately 6 to 10 h; 2) reduced levels of estradiol in ovarian venous blood, but elevated levels of estradiol in peripheral arterial blood of rabbits with estradiol impants. The inability to elevated estradiol to increase serum progesterone or weights of corpora litea suggests that the luteotropic effect is maximal when estradiol is present at physiological concentrations. Following the continuous administration of estradiol, ovarian secretion of estradiol appears diminished and the corpora lutea become dependent upon the exogenous estradiol for luteotropic support. Although the ovaries continue to release measureable quantities of estradiol, this is inmeasurable quantities of estradiol, this is insufficient to prevent regression of corpora lutea when exogenous estradiol is rapidly withdrawn from the circulation.

Animals↗
PubMed1975

Progesterone synthesis in developing rabbit corpora lutea in the absence of follicular estrogens.

We have investigated the role of 17beta-estradiol in the early development of the rabbit corpus luteum. Ectopic corpora lutea were established in all animals by autotransplanting preovulatory follicles beneath the kidney capsule 6.5 to 8 h after mating (day 0). At this time, the rabbits were bilaterally ovariectomized and in some of these rabbits a Silastic capsule containing crystalline 17beta-estradiol was implanted SC. Mean serum concentration of estradiol in rabbits with an estradiol impant was 16.4 pg/ml. In rabbits without an estradiol implant, the estradiol concentration averaged 1 pg/ml despite the presence of transplanted luteinized follicles. Daily blood samples were analyzed for progesterone by radioimmunoassay. Ectopic corpora lutea developed in rabbits with or without estradiol treatment. Serum progesterone concentrations in the two groups increased above castrate values and were not significantly different from one another through day 5. After day 5, progesterone concentrations steadily increased in rabbits treated with estradiol and reached a value of 4.8 ng/ml by day 10. In contrast serum progesterone steadily decreased after day 5 in rabbits without estradiol treatment to a level of 450 pg/ml by day 10. Hysterectomy on day 0 did not prevent this decline in progesterone, indicating that a uterine luteolytic agent was not involved. Total luteal weight on day 10 was positively correlated with serum progesterone concentration (r equals .92; P greater than 0.01). These results indicate that for a period of approximately 5 days afte r ovulation, the development of the rabbit ectopic corpus luteum and the secretion of progesterone are autonomous from estradiol secreted by ovarian follicles. After this time, there is an absolute requirement for estrogen which permits further development of the corpus luteum and the continuation of progesterone synthesis.

Animals↗
PubMed1971

Estrogen receptor in the rabbit corpus luteum.

The rabbit corpus luteum contains a cytoplasmic estrogen receptor substance in concentrations comparable to those found in the uterus. Receptor in corpora lutea of nonpregnant rabbits was highest at midluteal phase and decreased before physical regression of corpora was evident. These results support the view that the corpus luteum in this species is an estrogen-responsive tissue.

Animals↗
PubMed1969

Luteinizing hormone: action on the graafian follicle in vitro.

Graafian follicles, dissected intact from the rabbit ovary and incubated for 40 minutes with luteinizing hormone, developed into corpora lutea when autotransplanted under the kidney capsule. Follicles incubated with follicle-stimulating hormone or without hormone degenerated and failed to luteinize. Direct exposure of the mammalian follicle to luteinizing hormone initiates luteinization and formation of the corpus luteum.

Animals↗