A species difference between hamster and rat in the effect of oestrogens on growth of large preantral follicles

Sex steroids influence the plasma membrane transformation in the uterus of the fat-tailed dunnart (Sminthopsis crassicaudata, Marsupialia)

The uterine epithelium undergoes remodelling to become receptive to blastocyst implantation during pregnancy in a process known as the plasma membrane transformation. There are commonalities in ultrastructural changes to the epithelium, which, in eutherian, pregnancies are controlled by maternal hormones, progesterone and oestrogens. The aim of this study was to determine the effects that sex steroids have on the uterine epithelium in the fat-tailed dunnart Sminthopsis crassicaudata, the first such study in a marsupial. Females were exposed to exogenous hormones while they were reproductively quiescent, thus not producing physiological concentrations of ovarian hormones. We found that changes to the protein E-cadherin, which forms part of the adherens junction, are controlled by progesterone and that changes to the desmoglein-2 protein, which forms part of desmosomes, are controlled by 17β-oestradiol. Exposure to a combination of progesterone and 17β-oestradiol causes changes to the microvilli on the apical surface and to the ultrastructure of the uterine epithelium. There is a decrease in lateral adhesion when the uterus is exposed to progesterone and 17β-oestradiol that mimics the hormone environment of uterine receptivity. We conclude that uterine receptivity and the plasma membrane transformation in marsupial and eutherian pregnancies are under the same endocrine control and may be an ancestral feature of therian mammals.

The body has a brake: micrin is a postulated new gonadal hormone curbing tissue overgrowth and restricting reproduction

There is evidence for an unrecognised classical hormone secreted by the mammalian gonad. This postulated hormone--'micrin' (pronounced 'my-crin')--represents the body's brake against tissue overgrowth. When oestrogens are administered in high doses to female rats there is a considerable (non-artefactual) increase in the relative size and weight of organs such as the pituitary, adrenals, uterus and liver--suggesting an organotrophic (organ-building) role for endogenous oestrogens. This effect is exaggerated if the animals are first ovariectomized, indicating the removal of a negative ovarian factor, micrin. These organ enlargements can be reduced by pretreating the rats with large doses of antioestrogens such as clomiphene and tamoxifen. This antiestrogenic blockade of exogenous oestrogens is itself blunted by prior removal of the ovaries. It is proposed that antioestrogens (e.g. tamoxifen in breast cancer treatment) antagonize the organotrophic effects of oestrogens by competing for the oestrogen receptor peripherally and centrally and via an increase in the secretion of ovarian micrin. It is deduced that micrin is the testicular 'inhibin' proposed in the 1930s, not the molecule that now bears that name, which acts at the pituitary tier as a downregulator of follicle-stimulating hormone. The hallmark of micrin deficiency in the male rat is a pituitary hypertrophy that follows castration. This is reversible with a steroid-depleted aqueous bovine testicular extract, the micrin within which suppresses the hypothalamus, normalizing the pituitary. Micrin probably acts as a brake on peripheral tissues directly but also indirectly at the meta-level via the hypothalamic-pituitary axis, resetting a hypothalamic 'organostat' controlling organ and tissue masses, part of the 'organotrophic system' of internal size regulation. Besides endocrine (circulating) micrin from the gonads there is probably paracrine (locally acting) micrin produced in the brain. This is involved in a somatic cueing system for puberty: the brake comes off at an appropriate body tissue mass disinhibiting the hypothalamus and accelerating the organism towards sexual maturity and full adult stature. This suggests the use in reproductive disorders of micrin-related drugs. These could also be inhibitors of breast, prostate and other cancers, while protecting the bone marrow via a trophic effect on the adrenals (the lack of which protection causes lethal bone marrow depression in oestrogen-treated ferrets and dogs). Benign prostatic hyperplasia is asserted to be a micrin deficiency disorder, involving insufficiently opposed androgen. The rise in cancers with age could be associated with a reduction in micrin protection and a relative lack of this hormone could partly explain why men die younger than women. Micrin is dissimilar in activity to any known molecule and could usefully be isolated, characterised and exploited therapeutically.

Development of primordial follicles in the hamster: role of estradiol-17beta

The role of E2 on primordial follicle formation was examined by treating neonatal hamsters with 1 or 2 microg estradiol cypionate (ECP) at age postnatal d 1 (P1) and P4 or by in vitro culture of embryonic d 15 (E15) ovaries with 1, 5, or 10 ng/ml estradiol-17beta (E2). The specificity of E2 action was examined by ICI 182,780. One microgram of ECP maintained serum levels of E2 within the physiological range, significantly reduced apoptosis, and stimulated the formation and development of primordial follicles. In contrast, 2 microg ECP increased serum E2 levels to 400 pg/ml and had significantly less influence on primordial follicle formation. In vivo, ICI 182,780 significantly increased apoptosis and caused a modest reduction in primordial follicle formation. The formation and development of primordial follicles in vitro increased markedly with 1 ng/ml E2, and the effect was blocked by ICI 182,780. Higher doses of E2 had no effect on primordial follicle formation but significantly up-regulated apoptosis, which was blocked by ICI 182,780. CYP19A1 mRNA expression occurred by E13 and increased with the formation of primordial follicles. P4 ovaries synthesized E2 from testosterone, which increased further by FSH. Both testosterone and FSH maintained ovarian CYP19A1 mRNA, but FSH up-regulated the expression. These results suggest that neonatal hamster ovaries produce E2 under FSH control and that E2 action is essential for the survival and differentiation of somatic cells and the oocytes leading to the formation and development of primordial follicles. This supportive action of E2 is lost when hormone levels increase above a threshold.

Are estrogens of import to primate/human ovarian folliculogenesis?

The notion that estrogens play a meaningful role in ovarian folliculogenesis stems from a large body of in vitro and in vivo experiments carried out in certain rodent models, (e.g., rats) wherein the stimulatory role of estrogen on granulosa cell growth and differentiation is undisputed. However, evidence derived from these polyovulatory species may not be readily generalizable to the monoovulatory subhuman primates, let alone the human. Only recently, significant observations on the ovarian role(s) of estrogen have been reported for the primate/human. It is thus the objective of this communication to review the evidence for and against a role for estrogens in primate/human ovarian follicular development with an emphasis toward the application of the concepts so developed to contemporary reproductive physiology and to the practice of reproductive medicine. The role(s) of estrogens will be examined not only by analyzing the physiological evidence to the effect that these hormones control ovarian function and follicular growth, but also by summarizing the molecular evidence for the existence and distribution of the cognate receptors.

In vitro development of caprine ovarian preantral follicles

The in vitro growth and developmental pattern of caprine preantral follicles cultured in agar gel was observed. Preantral follicles 50 to 150 microm in diameter were isolated from prepuberal goat ovaries by treatment with collagenase and DNase. The isolated preantral follicles were cultured in agar gel for up to 14 days. A group of 10 follicles in different developmental stages was cultured in a culture well coated with 0.6% agar gel and filled with DMEM medium supplemented with FCS (10%), hypoxanthine (2 mmol/mL), dbcAMP (2 mmol/mL), FSH (100 ng/mL), insulin-transferrin-selenium (ITS) (50 ng/mL), IGF-1 (50 ng/mL), hydrocortisone (40 ng/mL) and antibiotics. Follicle viability was determined under an inverted phase-contrast microscope according to morphological and histological criteria, and follicle growth was assessed by their size and appearance. The results showed that the three-dimensional structures and forms of follicles were basically maintained intact during culture. Primary follicles developed into secondary follicles and a few of them into antral follicles. A large portion of secondary follicles entered the antral stage, and oocytes also acquired growth. The formation of theca lamina and zona pellucida was observed. The survival capacity of secondary follicles was greater than primary follicles. The survival rates for primary and secondary follicles were 11.36% (5/44) and 71.16% (53/74), respectively. During in vitro development the follicles demonstrated dominance. This experiment revealed the preliminary characteristics of the in vitro development of caprine preantral follicles.

Endocrine pathology of estrogens: species differences

The clinical uses of estrogens are associated with serious adverse effects, so the experimental toxicology of these compounds is under continuous review. Structurally different estrogens have qualitatively similar effects in animals when given in amounts way above the rodent uterotrophic dose. Toxicity still tends, however, to be related to estrogenic potency. Carnivores are more susceptible than rodents. Changes in reproductive, mammary and endocrine tissues are consistent with hyperestrogenism. Growth rate is decreased in rats and mice, but weight gains have been reported in other species. The weights of the liver, spleen, thymus and other organs are changed. Liver damage can occur. Susceptibility declines in the order cat, ferret, rat and mouse, dog. Clotting changes seen in the rat are secondary to liver damage. Moderate doses elicit anemia in rats, but lethal bone marrow depression in dogs and ferrets. Death is associated with hemorrhage. Antiestrogens modify aspects of estrogen toxicity in the rat, but not in the ferret. The predictive value of animal studies for humans has been disappointing. Interspecies variations at the hypothalamic-pituitary axis appear to have an important bearing on the differential activities of estrogens and antiestrogens across the species.

Species differences in estrogen receptors and in the response to 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure

The acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exhibits marked interspecies variability, with the guinea-pig, rat and hamster representing the species most sensitive, intermediate and most resistant to acute toxicity. Prepubertal guinea-pigs, rats and hamsters were treated with a single intraperitoneal injection of TCDD in olive oil at doses of 4, 50 and 1500 micrograms/kg, respectively. These exposures were chosen to produce acute toxicity and all 3 species exhibited a decrease in the rate of body weight gain during the 7 days following TCDD exposure when compared with control (olive oil-treated) animals. On the 7th day after exposure, the density and affinity of 17 beta-estradiol receptors were determined in the uterus and liver of TCDD-treated and control animals. The treatment with TCDD did not alter the affinity of the receptors in these 3 species. The density of hepatic 17 beta-estradiol receptors was decreased 65% in the guinea pig and 92% in the rat following exposure to TCDD. In contrast, TCDD-treated hamsters exhibited no change in the density of hepatic 17 beta-estradiol receptors. The uterine 17 beta-estradiol receptors were increased in density by TCDD treatment in the hamster and in the rat when expressed per mg protein. Uterine wet weights in the guinea-pig and rat were also significantly decreased by TCDD treatment but were not changed in the hamster. When the Bmax for uterine 17 beta-estradiol receptors was expressed as pmol/g tissue wet weight. TCDD exposure was found to produce an 11% decrease in density in the rat, while producing a 44% increase in the hamster. In control animals, the density of uterine 17 beta-estradiol receptors correlated inversely with the lethal dose of TCDD in these 3 species (i.e., the guinea-pig has the lowest LD50 and highest density of uterine 17 beta-estradiol receptors). The different responses to TCDD in the 3 species suggest that the changes in 17 beta-estradiol receptors may be related to species-specific toxic responses associated with TCDD exposure.

FSH-induced aromatase activity in hamster granulosa cells: effect of estradiol-17 beta in vitro

We have shown previously that estradiol-17 beta (E2) reduces number of ovulations in cyclic rats, induces atresia of the dominant preovulatory follicle in monkeys, and that the initial effects of this treatment include reduced viability and estrogen accumulation in vitro by aspirated granulosa cells (GC) from monkeys and hamsters. The present experiment was designed to determine whether the reduction in estrogen accumulation can be ascribed to a direct action of E2 on the aromatization of androgen to estrogen in vitro. Female hamsters were injected with 30 I.U. pregnant-mare serum gonadotropin i.p. and sacrificed 3 days later. GC were aspirated from the largest follicles and incubated for 48 h ("initial incubation" period) in the presence of human pituitary follicle-stimulating hormone (hFSH, 100 ng/ml). Following initial incubation, GC were further incubated for up to 24 h ("secondary incubation" period). During this subsequent incubation, medium was supplemented with 100 nM 3H-1 beta-androstenedione (3H-A4). Initial incubation with E2 at doses of 10 ng/ml, 100 ng/ml and 1 microgram E2/ml induced variability in GC response, and a maximal depression of approximately 70%. The inhibition by E2 of hamster GC function in vitro parallels that shown in vivo for both hamsters and monkeys, but contrasts with that shown for rats. Thus, hamsters may represent an appropriate model in which to study the atretogenic effects of E2 directly on antral follicle development.

Diminished steroidogenic response of hamster granulosa cells to estrogen in vitro

We have previously demonstrated that estrogen can exert inhibitory or atretogenic effects on the ovaries of both rats and rhesus monkeys in vivo. This study was designed to test whether the hamster (Mesocricetus auratus) is an appropriate model in which to test the effects of estrogens (diethylstilbestrol and estradiol-17 beta) on steroid accumulation by ovarian granulosa cells in vitro, and whether the effects are similar to those demonstrated for other species in vivo. Immature female hamsters were injected with pregnant mare's serum gonadotropin at 28 to 30 days of age. Animals were sacrificed and follicular contents aspirated three days later. Granulosa cells were either left untreated or treated with diethylstilbestrol or estradiol (1 X 10(-7) M) in vitro for 72 h in the presence of androstenedione (1 X 10(-7) M, and in the presence or absence of serum (10%) or human follicle-stimulating hormone (20 ng/ml), and long-term accumulation of estrogen and progesterone was determined. Diethylstilbestrol inhibited accumulation of estrogen regardless of the presence or absence of follicle-stimulating hormone. In contrast, only estradiol plus follicle-stimulating hormone augmented accumulation of progesterone by granulosa cells. These findings that estrogen can be non-stimulatory or inhibitory to function of granulosa cells in vitro parallel those shown in vivo. Our experimental approach may therefore represent an appropriate model for study of the direct effects of estradiol on the function of granulosa cells.

A quantitative and qualitative cytochemical analysis of glycosaminoglycan content in the zona pellucida of hamster ovarian follicles

In this study the amount of neutral and acidic glycosaminoglycans in the zona pellucida and antrum of primary, preovulatory, and atretic follicles was analyzed. Serial sections of preovulatory hamster follicles were stained with PAS or alcian blue to estimate the content of neutral and acidic glycosaminoglycans, respectively. The amount of hyaluronic acid, chondroitin sulfate and sialic acid was determined using enzyme digestion procedures followed by alcian blue staining. Microdensitometric analyses showed that the strongest PAS staining was in the zona pellucida of atretic follicles, less staining in preovulatory follicles but more than in the antrum of preovulatory follicles. No hyaluronic acid was found in the zona pellucida of any follicular type, but there was a measurable amount in the antrum of preovulatory follicles. Chondroitin sulfate was present in the zona pellucida of primary and atretic follicles, as well as in the antrum of preovulatory follicles. Sialic acid was present in the antrum and zona pellucida of all follicular types. Sialic acid plays a role in receptor recognition and its presence may reflect the role of the zona pellucida in sperm recognition and fertilization.

A daily rhythm in hCG binding to ovarian follicles of the cyclic hamster

On each day of the estrous cycle hCG binding to follicle increased from 09.00 to 21.00 h; then hCG binding was static until 09.00 h of the next day. FSH binding did not exhibit rhythmicity. This pattern of hCG binding may be related to the pulsing of LH on each cycle day.