Luteal function during the periimplantation period and requirement for estrogen for implantation and pregnancy maintenance in the non-human primate

An attempt has been made in this paper to review our present understanding of luteal function during the periimplantation period and in particular hormonal requirement for implantation and maintenance of early pregnancy in the non-human primate. In a fertile cycle thecorpus luteum is apparently rescued from luteolysis by chorionic gonadotropin secreted by the implanted blastocyst, In the bonnet monkey the serum progesterone titers during the luteal phase of a fertile cycle seems higher compared to that of nonmated cycling monkeys. This suggested that thecorpus luteum is receiving some stimulatory signal from the blastocyst even prior to implantation. The recent demonstration that human blastocyst in culture secretes into the medium human chorionic gonadotropin essentially support the above assumption. However, attempts to extend the luteal phase of cycling unmated monkeys with exogenous human chorionic gonadotropin injection has hitherto not met with complete success suggesting that there could be other than chorionic gonadotropin, additional luteal stimulatory factors the unimplanted blastocyst is secreting. Corpus luteum is the principle source of both progesterone and estrogen produced during the periimplantation period and dysruption of luteal function, brought about by either lutectomy or ovariectomy or luteinizing hormone antiserum treatment, followed by progesterone supplementation leads to maintenance of pregnancy. This has lead to questioning the need for estrogen in the maintenance of early pregnancy. Recent work using Zuclomiphene, an antiestrogen during days 5-11 of cycle in rhesus monkeys mated between day 9-14, has however, suggested that estrogen may be required for implantation. Further work is needed to arrive at an unequivocal decision regarding the need for estrogen in maintenance of early pregnancy in the primate

Gonadotropin regulation of rat ovarian lysosomes: existence of a hormone specific dual control mechanism

Gonadotropic hormones PMSG (15 IU/rat), FSH (3 μg/rat), LH (9 μg/rat) and hCG (3 μg/rat) were shown to decrease the free cytosolic lysosomal enzymes during the acute phase of hormone action in rat ovaries. When isolated cells from such rats were analyzed for the cathepsin-D activity, the granulosa cells of the ovary showed a reduction in the free as well as in the total lysosomal enzyme activities in response to FSH/PMSG; the stromal and thecal compartment of the ovary showed a reduction only in the free activity in response to hCG/PMSG. The results suggest the presence of two distinct, target cell specific, mechanisms by which the lysosmal activity of the ovary is regulated by gonadotropins

Development of an LH receptor assay capable of measuring serum LH/CG in a wide variety of species

The development of a radioreceptor assay (RRA) that can measure serum LH in a variety of species and CG in sera and urine of pregnant women and monkeys is reported. Using sheep luteal membrane as the receptor source and 125I-labelled hLH/hCG as the tracer, dose-response (displacement) curves were obtained using hLH or hCG as standard. The addition of LH-free serum (200 μl per tube) had no affect on the standard displacement curve. The assay is simple, requires less than 90 min to complete and provides reproducible results. The sensitivity of the assay was 0.6 ng hLH per tube and the intra- and interassay variations were 9.6 and 9.8, respectively. Sera obtained from male and female bonnet monkeys (Macaca radiata) and monkey pituitary extract showed parallelism to the standard curve. The concentrations of LH measured correlated with the physiological status of the animals. Sera of rats, rabbits, hamsters, guinea-pigs, sheep and humans showed parallelism to the hLH standard curve indicating the viability of the RRA to measure serum LH of different species. Since the receptors recognize LH and CG, detection of pregnancy in monkeys and women was possible using this assay. The sensitivity of the assay for hCG was 8.7 miu per tube. This RRA could be a convenient alternative to the Leydig cell bioassay for obtaining the LH bioactivity profile of sera and biological fluids

Effect of diethylstilbesterol and prolactin on the induction of follicle stimulating hormone receptors in immature and cycling rats

Induction of follicle stimulating hormone receptor in the granulosa cells of intact immature rat ovary by diethylstilbesterol, an estrogen, has been studied. A single injection of 4 mg of diethylstilbesterol produced 72 h later a 3-fold increase in follicle stimulating hormone receptor concentration as monitored by [125I]-oFSH binding to isolated cells. The newly induced receptors were kinetically indistinguishable from the preexisting ones, as determined by Lineweaver-Burk plot of the binding data. The induced receptors were functional as evidenced by increased ability of the granulosa cells to incorporate [3H]-leucine into cellular proteins. Neutralization of endogenous follicle stimulating hormone and luteinizing hormone by administering specific antisera had no effect on the ability of diethylstilbesterol to induce follicle stimulating hormone receptors, whereas blockade of endogenous prolactin secretion by ergobromocryptin administration significantly inhibited (~ 30 %) the response to diethylstilbesterol; this inhibition could be completely relieved by ovine prolactin treatment. However, ovine prolactin at the dose tried did not by itself enhance follicle stimulating hormone receptor level. Administration of ergobromocryptin to adult cycling rats at noon of proestrus brought about as measured on diestrusII, (a) a reduction of both follicle stimulating hormone (~ 30 %) and luteinizing hormone (~ 45 %) receptor concentration in granulosa cells, (b) a drastic reduction in the ovarian tissue estradiol with no change in tissue progesterone and (c) reduction in the ability of isolated granulosa cells to convert testosterone to estradiol in response to follicle stimulating hormone. Ergobromocryptin treatment affected only prolactin and not follicle stimulating hormone or luteinizing hormone surges on the proestrus evening. Treatment of rats with ergobromocryptin at proestrus noon followed by an injection of ovine prolactin (1 mg) at 1700 h of the same day completely reversed the ergobromocryptin induced reduction in ovarian tissue estradiol as well as the aromatase activity of the granulosa cells on diestrus II, thus suggesting a role for proestrus prolactin surge in the follicular maturation process

Use of tamoxifen, an antioestrogen, in establishing a need for oestrogen in early pregnancy in the bonnet monkey (Macaca radiata)

Administration of tamoxifen orally (3 mg/kg/day) during the post-ovulatory period from Days 16 to 20 or from Days 18 to 30 of female bonnet monkeys mated between Days 9 and 14 of the cycle resulted in inhibition of pregnancy establishment in 90-100% of monkeys tested. The pregnancy establishment in control female monkeys after exposure to the male during one ovulatory cycle was 66%. The effect of tamoxifen was not due to interference with luteal function because there was no reduction in serum progesterone concentrations after drug treatment. Exogenously administered progesterone could not reverse the inhibitory effect of tamoxifen on pregnancy establishment. The effect of tamoxifen was dose-dependent. We suggest that tamoxifen could be developed as an effective post-ovulatory contraceptive for regulation of female fertility

Antifertility effect of tamoxifen as tested in the female bonnet monkey (Macaca radiata)

The administration of a potent antiestrogen, tamoxifen at a dose of 3 mg/kg body weight/day orally post-coitally to cycling mated bonnet monkeys(Macaca radiata) from days 18-30 of cycle resulted in inhibition of establishment of pregnancy in 9 out of 10 monkeys. Tamoxifen effect was not due to interference with luteal function. The effect was specific to tamoxifen as exogenously administered progesterone could not reverse it. In addition to suggesting a role for estrogen in maintenance of early pregnancy in the primate the present study could be a prelude to the development of an effective post-ovulatory approach for regulation of fertility in the human female

Equine luteinizing hormone possesses follicle-stimulating hormone activity in hypophysectomized female rats

The ability of equine luteinizing hormone (eLH) to promote follicular growth and maturation in hypophysectomized rats has been assessed. A single injection of equine LH has been shown to promote the growth of a large number of antral and preovulatory follicles. In addition, equine LH markedly increased serum estrogen levels and uterine weight. Furthermore, equine LH, like equine chorionic gonadotropin (eCG; PMSG) was able to significantly enhance the incorporation of [3H]thymidine into ovarian DNA, an activity shown to be specific to hormones having follicle-stimulating hormone (FSH) activity. Equine LH treated with an FSH antibody immunoaffinity column to remove any possible contamination still exhibited the above activity, demonstrating that the FSH activity is intrinsic to the eLH molecule. Equine LH has also been shown to be capable of inducing LH receptors in granulosa cells of ovaries of hypophysectomized rats, an activity specific to FSH-like hormones. From the doses required of eLH and the degree of response observed, it is concluded, however, that eLH in the hypophysectomized rat is less active than eCG as an FSH

Studies on rat ovarian receptors for lutropin (luteinizing hormone). Interaction with β-subunit of sheep lutropin

By using radioimmunoassay, the interaction of sheep lutropin (luteinizing hormone, LH) β-subunit with rat ovarian receptors was investigated. The binding of β-subunit was specific, although of much lower order than that of lutropin. Sheep lutropin β-subunit effectively inhibited the binding of human choriogonadotropin (chorionic gonadotropin, gCG) to the ovary, showing that both occupy the same sites. The binding of sheep lutropin β-subunit to ovary was not followed by any detectable increase in cyclic AMP. The ovarian response to lutropin in terms of cyclic AMP production was inhibited in the presence of free β-subunit. The α-subunit of lutropin, when used at concentrations where contamination with whole lutropin was negligible, enhanced the degree of binding of β-subunit; this did not lead to increased cyclic AMP in the tissue. Surprisingly, the binding of β-subunit in vitro was drastically decreased by the prior removal of all endogenous rat lutropin bound to receptors. The implications of these data are discussed in the light of the reported biological activity of the β-subunit

Induction and inhibition of implantation in lactating rats

The interrelationship between prolactin and LH in the maintenance of pregnancy during lactation was studied. The reduction of suckled young from eight to two or less, as late as on the morning of Day 4 of pregnancy, resulted in normal implantation. Reintroduction of eight young on Day 4 to lactating pregnant rats deprived of their litters on Day 1 resulted in an inhibition of implantation, but reintroduction on Days 5 or 6 did not inhibit implantation. If oestrogen, HCG or PMSG was given on Day 4 of pregnancy, implantation was induced at the normal time in rats suckling large litters. When LH antiserum was given on the morning of Day 4 or Day 8 to pregnant rats suckling two young each, it blocked implantation and postimplantation survival of blastocysts, respectively. When the number of suckling young was increased from two to eight on Day 6, however, LH antiserum blocked pregnancy only to the extent of 70%. Prolactin administered during the preimplantation phase inhibited implantation in pregnant rats suckling a minimum number of young, but had no effect when given during the postimplantation phase. Progesterone failed to block implantation. Prolactin had no inhibitory effect on implantation in the absence of the suckling stimulus or in non-lactating pregnant rats. The inhibition of implantation by prolactin in rats suckling two young could be effectively reversed by the administration of oestrogen, PMSG or HCG on Day 4 of pregnancy

In vitro responsiveness of hamster corpora lutea undergoing luteolysis to luteinizing hormone

Corpora lutea removed from pregnant hamster deprived of endogenous luteinizing hormone for varying periods were compared for their responsiveness to externally added luteinizing hormone. The corpora lutea removed on the 8th day of pregnancy exhibited a dose-dependent increase in progesterone production in response to added luteinizing hormone upto a concentration of 2.5 μg/ml. The total progesterone synthesised by the corpora lutea decreased with increase in the duration ofin vivo luteinizing hormone deprivation. However, the hormone deprivation had to be for a minimum period of 24 h before a marked reduction in thein vitro responsiveness could be seen. Neutralisation of endogenous luteinizing hormone increased the luteal cholesterol ester concentration, whilein vitro incubation of such tissue with luteinizing hormone resulted in a marked reduction in cholesterol ester levels. Corpora lutea removed from hamsters on day 8, 15 and 16 of pregnancy when compared for their responsivenessin vitro to added luteinizing hormone showed that the luteal tissue of day 8 produced more progesterone relative to those of day 15/16. In contrast, depletion of free and esterified cholesterol increased with the increase in age of corpora lutea (from 15% on day 8 to 67% on day 16)