Estrogen receptor in rabbit ovaries and effects of antiestrogen on progesterone production

Effect of CDRI-85/287 on uterine estradiol and progesterone receptor levels/morphometric measurements during preimplantation period in rat

Studies with 85/287, a potent nonsteroidal antiestrogen/antiimplantation agent were taken up. In this paper we report alterations in uterine morphometric measurements and estrogen/progesterone receptor levels under the influence of this compound. Results showed 32% decline in stromal absolute volume density on day 5 post-coitum (p.c.) only, whereas eosinophilic leucocyte number decreased both on days 3 and 5 p.c. (41%) in treated rat uterus. Epithelial mitotic activity showed complete cessation both in control and treated rats on day 5 p.c. Under the influence of the compound both cytosolic and nuclear estrogen receptor (ERc and ERn) levels decreased on day 3 p.c., but on day 5 p.c. ERn increased significantly. A significant increase was however noticed in progesterone nuclear receptors (PRn) on day 5 p.c. On the whole our studies showed overall significant changes in uterine morphometric measurement/estrogen and progesterone receptor levels during the preimplantation period in rat under the influence of compound 85/287, causing asynchrony of events and thus failure of implantation.

Hormonal regulation of PKC-delta protein and mRNA levels in the rabbit corpus luteum

We have previously reported that rabbit corpora lutea exhibit a prominent phosphorylated substrate protein at 76 kDa which corresponds to the autophosphorylated form of protein kinase C (PKC) delta and that the expression of PKC-delta protein is increased in rabbit corpora lutea of pseudopregnancy at least 2-fold when serum estrogen levels are raised by the presence of an estrogen implant inserted at the time of human chorionic gonadotropin (hCG)-induced ovulation. The purpose of the experiments described herein was to evaluate further the hormonal regulation of PKC-delta in the rabbit corpus luteum. Results demonstrate that luteal PKC-delta protein and mRNA are concomitantly induced some 5-fold within 48 h in response to an ovulatory surge of hCG; that, as in corpora lutea of pseudopregnancy, luteal PKC-delta expression is relatively constant during the life span of the corpus luteum following a fertile mating; that exogenous estrogen does not modulate the induction of luteal PKC-delta during luteinization but promotes an additional two-fold increase in steady state PKC-delta mRNA (and protein) levels in corpora lutea by day 10 of pseudopregnancy; and that luteal PKC-delta expression can be abruptly and reversibly modulated upon withdrawal and subsequent replacement of an estrogen implant to pseudopregnant rabbits. These results demonstrate that an ovulatory surge of luteinizing hormone induces the expression of PKC-delta mRNA and protein in rabbit corpora lutea, and that once the corpus luteum becomes estrogen responsive, estrogen then regulates expression of PKC-delta mRNA and protein.

Estrogen withdrawal selectively increases serotonin reactivity in rabbit basilar artery

Clinical observations and laboratory investigations suggest that gender and menstrual status modulate cerebrovascular reactivity. We prepared 7 groups of rabbits (I) males (II) oophorectomized untreated females, (III) testosterone treated oophorectomized females, (IV) superovulated females, (V) superovulated estrogen withdrawn females, (VI) estrogen treated oophorectomized females, and (VII) estrogen withdrawn females to mimic phases of the estrous cycle and compare cerebral basilar artery reactivity to serotonin (5-HT) and norepinephrine (NE) in vitro. Basilar artery sensitivity to 5-HT vasoconstriction was increased in oophorectomized, acutely estrogen withdrawn females (Group VII) when compared to estrogen maintained and the other groups (p < 0.0001). There was a significant reduction in 5-HT sensitivity in superovulated females (Group IV) (p < 0.001). The change in 5-HT sensitivity is selective and was not observed for NE. Nitroarginine treatment and mechanical denudement resulted in higher Tmax and lower ED50 for both NE and 5-HT regardless of hormonal manipulation. We conclude that estrogen withdrawal increases 5-HT vasoreactivity by an endothelium independent mechanism.

Rapid vascular escape of arterially injected 16 alpha-radioiodo,17 beta-estradiol

PURPOSE

We undertook this study because confirmation of a rapid vascular escape and slow release back into the circulatory system suggests that arterial injection of radiohalogenated steroid receptor ligands might provide an efficacious route of administration for imaging or treatment of receptor-rich malignant tumors in peripheral tissues.

METHODS AND MATERIALS

We injected radiolabeled 16 alpha-iodo,17 beta-estradiol ([I]-E), an estrogen receptor ligand, into the femoral artery of swine in a solution that contained [125I]-E in a known ratio to [99mTc]-labeled red blood cells. Fractions of femoral venous blood were collected at short intervals during 10 min. We looked for changes in the ratio of the radiolabels. [99mTc]-labeled red blood cells are known to remain in the vascular system for an hour or more.

RESULTS

After passage of the injectate through the capillary bed of the swine leg, a dramatic decrease of the initial 125I:99mTc ratio to only 10% was observed in the femoral venous blood. This ratio increased gradually during the next 10 min to approximately 30% of that in the injectate, indicating that a significant portion (approximately 90%) of the [125I]-E was initially trapped in the limb and then slowly re-entered the vascular system. To obtain visual confirmation of the rapid vascular escape of iodo-estrogen, we injected either an imageable form of [I]-E (123I]-E) or [99mTc]-labeled red blood cells into the dorsal aorta of superovulated rabbits, whose smaller size allowed whole-body imaging. The biodistributions of these radiopharmaceuticals were surveyed continuously by real-time planar gamma imaging. Within 2 min after the injection of [123I]-E, the outlines of the circulatory system were entirely lost; however, some estrogen receptor-rich tissues (the ovaries) as well as some non-target tissues, for example, the lower leg extremities, yielded well-defined images. In contrast, after intra-arterial injection of [99mTc]-labeled red blood cells, the circulatory system remained sharply defined for the duration of the study (40 min).

CONCLUSION

A large fraction of [I]-E escapes from the vascular system during the first pass through an organ or limb, without regard to the estrogen receptor content of the tissue.

Estrogen and progesterone withdrawal increases cerebral vasoreactivity to serotonin in rabbit basilar artery

An in vitro animal model which examines the effects of sex hormone variations during the menstrual cycle on basilar artery reactivity is presented. Three groups of rabbits were utilized: a chronically depleted control group which received no further hormonal treatment after bilateral surgical oophorectomy (O), simulating menopause, and two groups of intact females, one of which was treated to mimic the estrogen and progesterone surge during the luteal phase (H) and the third group which was acutely estrogen and progesterone depleted after the luteal surges to simulate the immediate premenstrual state (W). We show that both acute and chronic estrogen and progesterone withdrawal significantly increase serotonin sensitivity (ED50) in basilar artery rings. There was no difference between groups for maximum contraction (Tmax) to serotonin, nor optimal resting tension. Furthermore, there was no difference in vasoreactivity and contractility to norepinephrine between groups. In order to distinguish between the effects of chronic and acute treatment we examined acute estrogen and progesterone superfusion in basilar artery rings from intact non-treated female rabbits. Acute superfusion of pre-contracted and non-pre-contracted artery segments resulted in significant dilatation only when supraphysiologic concentrations of estrogen and progesterone were used. We conclude that both acute and chronic female sex hormone withdrawal selectively increases cerebral vasoreactivity to serotonin.

Contraceptive efficacy of tamoxifen in female hamsters

Systemic administration of tamoxifen (trans-1-(4-B-dimethylaminoethoxyphenyl)-1,2-diphenyl-but-1-ene), an antiestrogen, at a dose level of 2 mg/kg body weight on days 1, 2 and 3 post-coitum (p.c.) intercepts pregnancy during the peri-implantation period in 70-80% of hamsters. Significant alterations in the circulating levels of estradiol and progesterone were accompanied by the abolition of peak activities of various uterine lysosomal enzymes in the treated animals. The present study, therefore, suggests that estrogen plays a crucial role during the process of ovum-implantation in hamsters, and tamoxifen displays an interceptive role in this species.

An immunocytochemical study of the progesterone receptor in rabbit ovary

Distribution of progesterone receptor (PR) was studied immunohistochemically in rabbit ovary and uterus using a monoclonal anti-receptor antibody. At the subcellular level, PR was located in cell nuclei of prepubertal rabbits, which were either non-treated, primed with estrogen or made pseudopregnant. At the tissue level, germinal epithelium, the external theca cell layer and granulosa cell layer were PR-positive. The internal theca cell layer had no PR immunoreactivity. The corpora lutea of pseudopregnant rabbits contained small amounts of PR in some of the animals. During pseudopregnancy, the distribution and staining intensity of PR-positive cells in the ovary was essentially similar to that in non-treated rabbits except for weak PR immunoreactivity in the internal theca cell layer. This differed significantly from the uterus, in which pseudopregnancy caused a marked decrease in PR immunoreactivity. This implies that receptor downregulation by endogenous progesterone is not the same in different organs and cell types. Immunohistochemical techniques give valuable information as to the steroid hormone target cell types and their distribution which are not available by conventional steroid-binding assays.

Cholesterol metabolism in estrogen-sensitive progestin synthesis by rabbit corpus luteum

To learn whether either reduced de novo cholesterol synthesis and/or altered cholesteryl ester metabolism is responsible for the deficient progestin production induced by estrogen withdrawal from pseudopregnant rabbits, we measured the luteal activity of three enzymes: 1) 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (the rate-limiting step in de novo cholesterol synthesis), 2) cholesteryl ester hydrolase, and 3) acyl coenzyme A:cholesterol acyltransferase (ACAT) in estrogen-stimulated and estrogen-deprived rabbits. The only change in the activity of these enzymes and of the enzyme NADPH-cytochrome c reductase (a microsomal marker enzyme) after estrogen capsule removal for 12 or 24 h was a 30% decrease in HMG-CoA reductase activity after 24 h. The decrease in HMG-CoA reductase activity was not accompanied by a detectable change in either the content or localization of cellular free cholesterol. Previous data from our laboratory have demonstrated that 24 h of estrogen deprivation has no effect on inner mitochondrial membrane P-450 side-chain cleavage activity (a rate-limiting step in the conversion of cholesterol to steroid hormones). These data, and our earlier finding that estrogen deprivation leads to accumulation of cholesteryl ester in the luteal cells, indicate that estrogen maintains rabbit luteal progestin production by stimulating the transfer of cytoplasmic cholesterol to the active site of P-450 side-chain cleavage on the inner mitochondrial membrane.

Nuclear estrogen receptor bindings in granulosa cells and estradiol-17 beta contents in follicular membranes of the ovary of the hen during the ovulatory cycle

Estrogen receptors were found in the nuclear fractions of granulosa cells of the largest (F1) and the second largest (F2) preovulatory follicle in the ovary of the hen. The maximum number of binding sites (NBSmax) of the nuclear estrogen receptors was greater in F2 than in F1, while the equilibrium dissociation constant (Kd) was not different. During the ovulatory cycle, the NBSmax of the estrogen receptors showed a change parallel to the change in the estradiol-17 beta content in the follicular membranes. The results suggest that estradiol-17 beta produced in the follicular membrane may exert a direct action on the granulosa cells in the hen ovary.

A possible mechanism in arterial wall for mediation of sex difference in atherosclerosis

Female rabbits on an atherogenic diet were treated with cottonseed oil (control), tamoxifen, testosterone, or progesterone. After 10 weeks the rabbits were killed, the aortas quickly removed, graded for atherosclerosis, and incubated with [14C]proline to determine collagen and elastin synthesis. Rabbits treated with testosterone and progesterone had the greatest degree of atherosclerosis, the highest DPM in hydroxyproline of collagen and elastin, and the greatest accumulation of collagen and elastin in the aorta. Tamoxifen-treated rabbits had less incorporation of radioactivity. In separate experiments aortas of similarly treated rabbits were analyzed for estradiol and progesterone receptor density. These receptors were found to be present, and progesterone and testosterone administration caused a translocation of progesterone receptors from cytosol to nucleus. Results are consistent with the hypothesis that sex hormones can affect the development of atherosclerosis through a direct effect of the hormones on arterial wall to alter collagen and elastin synthesis, the effect being mediated through hormone receptors in the wall.

Effect of clomiphene citrate on the rabbit ovary

The effect of clomiphene citrate on the rabbit ovary was studied in mature nulliparous rabbits pretreated with three consecutive doses ranging from 0.01-10.0 mg/kg per day. With increasing doses a trend of decrease in mean ovarian weight (mg/kg body weight) is observed 2 days after termination of treatment. Five days later a significant increase occurs, which then subsides again to control values on day 12 after termination of treatment. During this period, no matings or injections of luteinizing hormone were performed to trigger ovulation; consequently no ovulations are observed. Folliculogenesis appears as normally; number and morphology of follicles are within normal ranges. No endogenous, spontaneous gonadotropin surges are detected in blood serum up to the 7th day after termination of treatment (2 and 10 mg doses). The surface epithelium of the ovary resembles normal germinal epithelium; however, after treatment with high doses a "secretory"-like activity is observed, accompanied with ultrastructural changes.

Monoclonal antibody recognition of estrogen receptor in rabbit corpus luteum

We demonstrated previously by administering [3H]estradiol and using autoradiography that, in vivo, the exogenous estradiol that will sustain progesterone production is sequestered to nuclei of the luteal cells in corpora lutea of pseudopregnant rabbits. Our objective in the present experiments was to use an immunological method to demonstrate that estrogen receptor of the rabbit corpus luteum is associated with this uptake. For this purpose, we prepared nuclear extracts from corpora lutea removed from anesthetized pseudopregnant rabbits 10 min after arterial infusion of 125I-estradiol. These extracts were then analyzed by sucrose density gradient centrifugation in the presence and absence of monoclonal antibody against human breast cancer estrogen receptor. We found that the 125I-estradiol-binding component extracted with 0.5 M KCl from the nuclear pellet sediments in the 3-4S region in high-salt gradients; in the presence of monoclonal antibody (D-547 Sp2 gamma), the entire estradiol-binding component is shifted to the 8-9S region, indicating the formation of immunocomplex with the 125I-estradiol-receptor moiety. The principal estradiol-binding component that can be observed in the 3-4S region of high-salt gradients of cytosol of rabbit corpora lutea reacts with this antibody regardless of whether 125I- or [3H]estradiol is given in vivo or in vitro. In both cytosol and nuclear extracts of luteal tissue, unlabeled diethylstibestrol totally inhibits the binding of radiolabeled estrogen to this antibody-shifted 125I- or [3H]estradiol-binding moiety; neither progesterone nor testosterone inhibit binding of radiolabeled estrogen to the antibody-shifted moiety. From these findings we conclude that sequestering of estradiol by the rabbit corpus luteum in vivo is accomplished by the steroid-specific estrogen receptor that shares characteristics of the estrogen receptor found in human breast cancers, including a) antigenic features and b) the capacity to translocate estrogens from the cytosol to the nuclear fraction.

Site of estrogen action in rabbit ovarian tissue

In superovulated or naturally mated pseudopregnant rabbits, an abrupt premature decline of progesterone production by the corpus luteum occurs after removal of polydimethylsiloxane capsules filled with 17 beta-estradiol. Reinsertion of the estradiol-filled capsules stimulates a striking restoration of progesterone production. We have given [3H]estradiol by arterial infusion to anesthetized rabbits to determine by cellular autoradiography whether the exogenous estradiol localizes to luteal tissues responsible for progesterone production. Autoradiography with both freeze-dried and touch-thaw mounted preparations demonstrated that tritium activity localized to the nuclei of luteal cells and that such uptake could be blocked by radioinert diethylstilbestrol. We extracted the tritium activity sequestered in vivo by the corpora lutea and cocrystallized the extract with 14C-labeled and radiostable 17 beta-estradiol to confirm its presence (greater than 90%) as [3H]estradiol. In addition, we were able to demonstrate that radiostable diethylstilbestrol blocked ovarian uptake of 16 alpha-125I-17 beta-estradiol in vivo. In concert, these observations provide compelling evidence that the exogenous estradiol responsible for restoring progesterone production may act through an estrogen-specific mechanism directly in the luteal cells.

Antiestrogenic and antifertility actions of Anordrin (2 alpha, 17 alpha-diethynyl-A-nor-5 alpha-androstane-2 beta, 17 beta-diol 2,17-dipropionate)

Anordrin, administered in a single s.c. dose of 62.5 micrograms in sesame oil, stimulated sustained uterine growth (wet weight) when measured at 24 and 72 hr, but total soluble protein and total DNA per uterus was not increased. By comparison, 3 micrograms of estradiol-17 beta under the same conditions significantly increased all three parameters of uterine growth. Both of the above steroid treatments significantly increased nuclear estrogen receptor content of the uterus, but only the estradiol-17 beta treatment resulted in significantly elevated cytosol receptor content per uterus. Anordrin binds to the 8S estrogen receptor with an affinity of about 2 x 10(5) M-1 as determined by competition with [3H]estradiol-17 beta. The abortifacient activity of Anordrin when given orally (8 mg/kg b.w.) to mice on the 7th day of pregnancy was almost completely blocked by simultaneous oral administration of estradiol-17 beta (0.8 mg/kg b.w.). It is concluded that the actions of Anordrin on the uterus can be attributed to its antiestrogenic activities.