Cytosol Progestin Receptor Concentrations Research Articles

Biochemical and Immunocytochemical Assessment of Neural Progestin Receptors Following Estradiol Treatments that Eliminate the Sex Difference in Progesterone‐Facilitated Lordosis in Guinea‐Pigs

Abstract A single injection of estradiol benzoate (10 mug), while highly effective in ovariectomized female guinea-pigs, does not prime castrated males to display progesterone-facilitated lordosis. In contrast, adult males and females exhibit the same, high degree of progesterone-facilitated lordosis when primed with two, 2.0 mug injections of free estradiol-17ss (pulse regimen). We compared neural progestin receptor induction after these different estradiol treatments by in vitro radioligand binding assays and immunocyto-chemistry. Binding assays confirmed previous observations of lower concentrations of cytosol progestin receptors in the mediobasal hypothalamus-preoptic area in estradiol benzoate-treated males than in females. No such sex difference was observed in animals that had been exposed to the behaviorally effective estradiol pulse regimen; rather, hypothalamic-preoptic area progestin receptor concentrations in these animals did not differ from the low levels observed in males treated with the behaviorally ineffective estradiol benzoate regimen. Immunocytochemical analysis revealed progestin receptor-immunoreactivity in fewer cells in the medial preoptic nucleus-anterior hypothalamic nucleus, periventricular preoptic area and arcuate nucleus of estradiol pulse- as compared to estradiol benzoate-treated males and females. Estradiol benzoate treatment induced progestin receptor-immunoreactivity in more cells in the medial preoptic area and ventrolateral hypothalamus than estradiol pulses in males, but not in females. Surprisingly, in these regions estradiol benzoate-treated males had significantly more progestin receptor-immunoreactive cells than females. These experiments yield two major findings: First, as has been shown in rats, the display of progesterone-facilitated lordosis is not inflexibly differentiated according to sex in guinea-pigs. Furthermore, reduced concentrations of estradiol-induced progestin receptors in the hypothalamus and preoptic area cannot account for the lack of progesterone-facilitated lordosis that is observed following priming with estradiol benzoate in males. Secondly, in the medial preoptic area and ventrolateral hypothalamus of female guinea-pigs, estradiol pulses are as effective as estradiol benzoate in inducing progestin receptors. These observations, taken together with the finding of equal behavioral efficacy of the two estradiol treatments, are consistent with the hypothesis that estradiol-induced progestin receptors in these regions of the brain are involved in progesterone-facilitated lordosis in female guinea-pigs.

Long-term ovariectomy and hormone-induced sexual behavior, progestin receptors, and hypothalamic morphology in female rats

Long-term ovariectomy reduces the ability of estradiol and progesterone treatment to induce sexual receptivity in female rats. Previous researchers suggested that this effect may be due to a decreased induction of neural progestin receptors by estradiol in the long-term ovariectomized rats. The present study was designed to replicate and extend this finding, and to search for neuroanatomical correlates by measuring the volume of the ventromedial nucleus (VMN) of the hypothalamus, a putative site of action of estradiol and progesterone for the induction of female sexual behavior. Long-term ovariectomy (5 to 6 weeks) as compared to short-term ovariectomy (1 week) reduced the ability of estradiol-17β and progesterone treatment to induce sexually receptive and proceptive behaviors. Consistent with previous reports, our data show that the reduced levels of cytosol progestin receptors after long-term ovariectomy and estradiol treatment are related to a reduced ability of estradiol to induce the receptors. Long-term ovariectomy did not affect the concentration of cytosol progestin receptors in the preoptic area, suggesting a neuroanatomical specificity to this effect. Contrary to our predictions, long-term ovariectomy did not affect the volume of the VMN. In fact, estradiol treatment, while blocking the effect of long-term ovariectomy on sexual behavior, decreased the volume of the VMN. Therefore, the measurement of the volume of the VMN is not a good predictor of the responsiveness to steroid hormone induction of sexual behavior.

Steroids induce hypothalamic progestin receptors and facilitate female sexual behavior in neonatal rats

This report provides the first evidence that two activational actions of estrogen can occur within the first week of life in the rat. Priming 4-day-old rats with exogenous estradiol benzoate facilitates lordosis and ear wiggling-like behavior, and induces cytosol progestin receptors in the medial basal hypothalamus and preoptic region (Hyp-PoA) 44 h later. Moreover, unprimed male infants show more intense lordosis and higher concentrations of cytosol progestin receptors in Hyp-PoA than infant females. Neonatal castration of male infants decreases their concentration of cytosol progestin receptors in Hyp-PoA to the levels normally seen in infant females. In addition, priming 6-day-old infants with progesterone alone facilitates lordosis in male but not female infants. Together, these data demonstrate that in the male infant, endogenous steroids of testicular origin have activational as well as organizational actions.

Cell nuclear accumulation of estrogen receptors in rat brain and pituitary gland after treatment with a dopamine-beta-hydroxylase inhibitor.

In a recent experiment, it was found that the dopamine-beta-hydroxylase inhibitor, U-14,624, decreases the concentration of cytosol progestin receptors in guinea pig hypothalamus and causes an increase in the concentration of nuclear progestin receptors. In this series of experiments, the possibility that similar effects would be seen in the rat estrogen receptor system in mediobasal hypothalamus and pituitary was tested. U-14,624 caused a time-dependent decrease in the concentration of cytosol estrogen receptors and increase in the concentration of nuclear estrogen receptors in both mediobasal hypothalamus and anterior pituitary gland in ovariectomized rats, both in the absence and presence of low levels of estradiol, as well as in ovariectomized-adrenalectomized rats. The nuclear estrogen receptors that accumulate after U-14,624 injection do not require incubation at 25 degrees C to be assayed, suggesting that they are not occupied by an estradiol-like ligand. The nuclear estrogen receptors that accumulate after U-14,624 treatment are high affinity, with an apparent dissociation constant of approximately 0.1 nM. U-14,624 does not compete with (3H)estradiol, in vitro, suggesting that it does not directly interact with estrogen receptors. These results suggest that under some conditions, inhibition of dopamine-beta-hydroxylase causes a modification in unoccupied estrogen receptors so that they develop a higher affinity for cell nuclear components.

Short-term effects of danazol and medroxyprogesterone acetate on cytosol and nuclear estrogen and progestin receptors, 17 beta-hydroxysteroid dehydrogenase activity, histopathology, and ultrastructure of human endometrial adenocarcinoma.

We measured concentrations of cytosol and nuclear estrogen, as well as progestin receptors and activities of 17 beta-hydroxysteroid dehydrogenase (17-HSD), and examined histopathology and ultrastructure of endometrial carcinoma specimens taken before and after one-week danazol (200 mg, 3 times daily) or medroxyprogesterone acetate (MPA, 100 mg daily) treatments in 14 and 16 patients, respectively. A typical progestin effect, a significant increase in the activity of 17-HSD, was observed after both treatments. The post-therapy 17-HSD activities correlated significantly with the pretreatment cytosol progestin receptor concentrations in both treatment groups. Both MPA and danazol decreased the proliferative activity and increased the secretory activity of the malignant epithelial endometrial cells. These biochemical and morphological results support the concept that danazol has progestin-like actions on the human endometrium, and might therefore be an alternative for hormonal treatment of endometrial carcinoma.

Demonstration of progestin receptors in human vaginal epithelium.

The presence of a high-affinity and limited-capacity progestin receptor was demonstrated in the human vaginal epithelium. The sedimentation coefficients of the receptor were 8.5 S and 5 S. Both nuclear and cytosol progestin receptor concentrations varied considerably during both the follicular and the luteal phase of the cycle. In postmenopausal women no correlation was found between the receptor concentrations and the dose and type of estrogens given.

Noradrenergic inhibitors cause accumulation of nuclear progestin receptors in guinea pig hypothalamus

A series of experiments was performed to study the possible behavioral relevance of the apparent regulation of hypothalamic cytosol progestin receptors by noradrenergic transmission in female guinea pigs. In the first experiment, ovariectomized guinea pigs were injected with estradiol benzoate followed 36 h later by the dopamine-β-hydroxylase inhibitor, U-14,624 or vehicle. Twelve h later, they were injected with progesterone and tested hourly for sexual behavior. Six h after the progesterone injection, a time at which inhibition of sexual behavior by the U-14,624 was confirmed, they were killed, and cytosol and nuclear progestin receptors were assayed in the hypothalamus and cerebral cortex. No difference was seen in the concentration of progestin receptors after drug treatment in these animals that also received a progesterone injection. In subsequent experiments, it was found that the U-14,624-inhibition of progesterone-facilitated sexual behavior is not accompanied by an inhibition of nuclear progestin receptor accumulation. Furthermore, it was found that the decreased cytosol progestin receptor level caused by U-14,624 prior to progesterone injection was accompanied by an increase in the concentration of nuclear progestin receptors. The increase in nuclear progestin receptors was also seen after treatment with the α-adrenergic antagonist, prazosin, U-14,624 does not compete with [ 3H]R 5020 for binding to the progestin receptor, suggesting that it does not directly cause translocation of progestin receptors. The results of these experiments suggest that the decrease in the concentration of cytosol progestin receptors caused by noradrenergic inhibitors is not due entirely to an interference with the formation of cytosol progestin receptors. Rather, it seems that these drugs, in some way, also cause the accumulation of progestin receptors in cell nuclei. Furthermore, they suggest that the mechanism by which these drugs inhibit sexual behavior may not be by interference with the progestin receptor system.

Nuclear estradiol and cytosol progestin receptor concentrations in the brain and the pituitary gland and sexual behavior in ovariectomized estradiol-treated middle-aged rats.

We wished to determine whether the altered nuclear estradiol (E2) receptor concentrations in middle-aged rats can explain the diminished responsiveness to E2 observed in aging rats. Therefore, we measured receptor concentrations in various brain areas and the pituitary gland of young and middle-aged ovariectomized rats 2 and 4 days after implantation of Silastic capsules containing E2. To determine whether any observable changes had physiological consequences, we correlated age-dependent changes in E2 nuclear receptor concentrations with two E2-dependent parameters: cytosol progestin receptor levels in equivalent brain areas and pituitary gland and progesterone-facilitated reproductive behaviors. Young (3-4 months old) and middle-aged (10-12 months old) Sprague-Dawley rats were ovariectomized and received Silastic capsules containing E2 dissolved in oil 1 week later (day 0). Groups of rats were killed at 1200 h on either day 2 or day 4. Nuclear E2 and cytosol progestin receptor concentrations were assessed in a nuclear and cytoplasmic extract from the medial basal hypothalamus, preoptic area, amygdala, and pituitary gland. To test steroid-induced mating behavior, ovariectomized young and middle-aged rats were treated with E2-containing capsules for 2 or 4 days. At 0900 h progesterone (0.2 mg/kg BW) was injected sc and receptive and proceptive behaviors were observed when experienced males were introduced 4-6 h later. Two days after implantation of E2 capsules, middle-aged rats exhibited lower nuclear E2 receptor concentrations in the medial basal hypothalamus and preoptic area than young rats. By day 4, there were no significant age-related differences in any brain area or in the pituitary gland. Parallel age-related differences were observed in cytosol progestin receptor concentrations on day 2 but they were not evident by day 4. Similarly, middle-aged rats exhibited deficits in proceptive behavior, lordosis quotient, and lordosis quality score on day 2, but there were no differences compared to young rats on day 4. These data demonstrate that E2-induced nuclear E2 receptor concentrations are lower in selected areas of the brain of middle-aged rats. Such changes appear to be physiologically important because they are correlated with changes in E2-induced cytosol progestin receptor concentrations and steroid-induced behaviors. Furthermore, they may partially account for age-related differences in E2-induced LH surges on day 2.(ABSTRACT TRUNCATED AT 400 WORDS)

The relationship between heat abbreviation and neural progestin receptors in female rats

The purpose of this study was to determine whether changes in the levels of neural progestin receptors are associated with mating-induced heat abbreviation in the rat. Mating caused a decrease, 8–10 hr after stimulation, in the duration of sexual receptivity. No difference in the concentration of cytosol progestin receptors was found between mated and nonmated animals 8–10 hr after treatment. Mating caused a statistically significant decrease in the concentration of nuclear progestin receptors at that time. However, this difference was probably not related to heat abbreviation, because no difference in nuclear progestin receptor levels was found between animals mated with vaginal masks and animals mated without masks, while mated-masked animals were found to exhibit significantly higher levels of sexual receptivity than mated-nonmasked animals after treatment. In addition, mating either with or without masks caused a statistically significant increase in serum progesterone levels relative to that measured in nonmated animals. Therefore, it is suggested that mating, even in the absence of cervical-vaginal stimulation, may cause the release of adrenal progestins which, in turn, may influence the rate at which neural progestin receptors accumulate and are processed within cell nuclei. The results of the present study suggest that mating-induced heat abbreviation in the rat is not associated with decreased levels of neural cytosol or nuclear progestin receptors.

Estrogen receptors and estrogen-inducible progestin receptors in the sexual skin of the monkey

Estrogen-binding macromolecules were identified in sexual skin cytosol and nuclear fractions from female Japanese monkeys ( Macaca fuscata fuscata), by sucrose-glycerol gradient analysis and dextrancoated charcoal adsorption technique. Furthermore, using the highly potent synthetic progestin, R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione; promegestone), progestin-binding macromolecules were detected in sexual skin cytosols from ovariectomized estrogen-primed monkeys. Both cytosol components sedimented at the 8S region on sucrose-glycerol gradients and had a highaffinity for the respective steroids, and competition studies showed a specificity for estrogenic, or progestational compounds. The concentration of cytosol progestin receptors was markedly increased with the elevated level of nuclear estrogen receptors following estrogen priming. The above results demonstrate the existence of cytosol and nuclear estrogen receptor sites, and estrogen-induced progestin receptors in the sexual skin of the female monkeys.