Cytosol Progestin Receptors Research Articles

Effects of testosterone on morphology and on progestin and estrogen receptor levels in the mouse uterus and mammary gland.

The effects of androgen on the morphology and levels of cytosolic estrogen and progestin receptors (ER and PR) were studied in the mouse uterus and mammary gland. Testosterone neonatally and/or continuously in the adult lowers ER and PR levels particularly at early ages (40-60 days of age) in both the uterus and mammary gland. At older ages, less prominent changes in ER and PR levels are observed. Neonatal androgen treatment appears to exert both direct effects on the uterus and mammary gland and indirect effects (via the hypothalamo-hypophysio-ovarian axis). At all ages, neonatal testosterone in combination with continuous adult testosterone consistently depressed PR levels in both uterus and mammary gland, indicating that testosterone is a negative modulator of PR in these tissues.

The role of androgen receptors in sexual differentiation of the brain: Effects of the testicular feminization (Tfm) gene on androgen metabolism, binding, and action in the mouse

The effects of the testicular feminization (Tfm) mutation on androgen metabolism, binding, and action were studied in the mouse. Cytosolic binding of [3H] dihydrotesterone (DHT) was reduced by approximately 90% in the brains, pituitaries, submaxillary glands, and kidneys of Tfin/Y males, as compared to wild-type male controls. Nuclear [3H] DHT binding was abolished in tissues from Tfm male animals. Implantation of testosterone-containing (T-containing) Silastic capsules elevated nuclear estrogen receptor (ERn) concentrations to a similar extent in the brains of all four genotypes studied (normal males, Tfm-affected males, normal females, and Tfm carrier females). Administration of T to normal males led to elevations of cytosolic progestin receptors (PRc) and monoamine oxidase (MAO) activity in the brain, and of alcohol dehydrogenase (ADH) and glucose-6-phosphate dehydrogenase (G6PDH) in the kidney. In Tfm-affected males, only the PRc response to T was observed, at a somewhat reduced level compared to that in normal male and female controls: no effect of T was observed with respect to either MAO in the brain, or ADH and G6PDH activities in the kidney. Estradiol (E2) administration increased the activity of pituitary G6PDH and lactic dehydrogenase (LDH) in all four genotypes. However, brain MAO activity was increased by E2 only in normal and carrier females. The lack of an MAO response to E2 in Tfm-affected males is consistent with the hypothesis that the central nervous system of this genotype is at least partially masculinized, despite the loss of androgen receptor-mediated responses—most probably as a result of local conversion of T to E2 within the brain itself.

Effects of gonadectomy and hormone replacement on steroid hormone receptors and 5 alpha-reductase activity in pituitaries of male rhesus macaques.

We measured androgen, estrogen, and progestin receptors and 5 alpha-reductase activity in the anterior and posterior pituitary gland of intact and 6-week castrate adult male rhesus monkeys and castrate males which were treated with testosterone (T) or estradiol (E) from time of surgery. Saturation analysis of anterior pituitary tissues from monkeys receiving various treatments revealed an apparent mean dissociation constant (Kd) of 0.53 +/- 0.17 (+/- SE) X 10(-10) mol/L (n = 3) for [3H]R1881 (androgen) binding to cytosol, 2.6 +/- 0.50 X 10(-10) mol/L (n = 3) for [3H]R2858 (estrogen) binding to cytosol, 1.7 X 10(-10) mol/L (n = 2) for [3H]R5020 (progestin) binding to cytosol, and 6.2 X 10(-10) mol/L (n = 2) for [3H )R1881 binding to cell nuclear extract. The highest levels of nuclear androgen receptor (AR) were found in intact males [37.1 +/- 3.5 (+/- SE) fmol/mg DNA; n = 7] and castrated males treated with T for 6 weeks (89.7 +/- 30.2 fmol/mg DNA; n = 5). High levels of nuclear AR corresponded to serum T levels and low serum LH levels. Nuclear AR was undetectable in castrated males and castrated males treated with E. Significantly greater levels of cytosolic AR were detected in intact males (27.5 +/- 1.6 fmol/mg protein) compared to all other groups (P less than 0.05). T or E treatment had no effect on cytosolic AR. Increased levels of cytosolic progestin receptor were found in intact monkeys and after E or T treatment compared to levels in untreated castrates. No differences in 5 alpha-reductase activity were found between any treatment groups. These data indicate that anterior pituitary nuclear androgen receptor is correlated with serum LH levels and support the hypothesis of a direct action of T on anterior pituitary LH secretion. In addition, it appears that cytosolic progestin receptor, but not AR, is regulated by estrogen in intact male rhesus monkeys. In the posterior pituitary, AR dynamics followed a profile in which cytosolic AR increased after castration and decreased after T treatment. Nuclear AR decreased after castration and increased after T treatment. The presence of a dynamic AR system in the posterior pituitary suggests hormonal regulation of its function by androgens.

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.

Dynamics of oxytocin, estrogen and progestin receptors in the bovine endometrium during the estrous cycle.

The levels of oxytocin receptor (OTR), cytosolic progestin receptor (cPR), cytosolic and nuclear estrogen receptor (cER, nER) were measured in the endometrium of 28 heifers that had been slaughtered on a defined day of the estrous cycle. In an additional, trial endometrial tissue obtained from 78 heifers or cows at the abattoir was analysed for OTR. OTR was absent during the luteal phase (after day 6), but a minor elevation was observed after day 15. OTR increased rapidly after luteolysis on days 17-18 reaching a maximum during estrous on day 21, and decreased again during days 1-6. cER and cPR were different to OTR but followed a similar pattern with maximal levels during days 1-8 of the estrous cycle. At day 12 both receptors were minimal and increased again towards day 21. nER was maximal at day 19-21 coinciding with maximal estradiol levels and estrous. Our data indicate that owing to an increasing sensitivity of the endometrium to progesterone and estradiol after day 12, these steroids may be mainly responsible for the initiation of first PGF2 alpha surges and luteolysis. Oxytocin seems to be of minor importance at this stage owing to low sensitivity of the endometrium for oxytocin.

Effects of hypothalamic serotonin depletion on lordosis behavior and gonadal hormone receptors

The effects of chronic depletion of serotonin on feminine sexual behavior (lordosis), cytosolic progestin receptors and estradiol nuclear receptors were investigated. Intrahypothalamic administration of 5,7-dihydroxytryptamine (5,7-DHT) markedly enhanced lordotic responding in estradiol benzoate (EB)-primed, 5,7-DHT-treated female rats and in EB-progesterone primed, 5,7-DHT-treated male rats. Cytosolic progestin receptors were measured in preoptic-hypothalamic nuclei related to reproductive function in sham and 5,7-DHT-treated rats after EB priming. In both sexes, no differences between sham and 5,7-DHT-treated subjects were noted for progestin binding in the medial preoptic nucleus, ventromedial nucleus or arcuate-median eminence area. Estrogen-nuclear complexes were measured in the same brain nuclei of female rats following EB priming, and no differences between sham and 5,7-DHT-treated rats were found. Under the conditions employed, it would appear that, despite marked elevations in lordotic responsivity, the accumulation of estrogen nuclear receptors and the levels of estrogen inducible progestin receptors remain unaltered after chronic depletion of serotonin. Thus, serotonergic influences on lordosis do not appear to involve changes in the expression of steroid receptor levels in preoptic-hypothalamic nuclei known to mediate hormone-dependent neuroendocrine processes.

Neuroendocrine changes in female rats born from streptozotocin-diabetic mothers.

In adult female rats born from Streptozotocin-diabetic mothers, blood glucose measured under basal conditions or 30 min after glucose administration was similar to controls; however at 180 min 50% of offspring from diabetics was moderately hyperglycemic whereas 100% of controls were normoglycemic. The time of vaginal opening, and after maturity, the number of rats with regular estrous cycles was in the range of controls. After ovariectomy, control rats receiving estradiol showed a sharp increase of serum LH at 4 pm following progesterone treatment at 10 am, while rats born from diabetic mothers failed to modify serum LH. Estradiol receptors in cell nuclei and cytosolic progestin receptors were determined in anterior pituitary, hypothalamus and preoptic area of rats subjected to a 4-day estradiol treatment. Changes were statistically significant in the hypothalamus only, in that rats born from diabetic mothers showed reduced induction of progestin receptors coupled to increased binding of (3H)-estradiol in cell nuclei. These findings bring support for a hypothalamic defect in rats born from diabetic mothers, the reduction of hypothalamic progestin receptors being reflected in the reduced sensitivity to the positive feedback action of progesterone to release LH.

Are cytosol estrogen and progestin receptors of prognostic significance in the management of epithelial ovarian cancer?

Cystosol estrogen and progestin receptor levels in tumor samples from 101 patients with previously untreated primary epithelial ovarian cancers were correlated with patient survival. Patients with stage I and II disease whose tumors contained elevated levels of cytosol progestin receptors had an improved survival over patients with tumors containing low levels of cytosol progestin receptors. However, patients with advanced ovarian cancers and low cytosol progestin receptors had significantly longer survival. The four-year estimated duration of survival with advanced disease and cytosol progestin receptors less than seven was 82%, whereas if the cytosol progestin receptors were seven or more, the four-year estimated duration of survival was only 10%. The explanation for this dichotomy is not evident at this time. In this study cytosol estrogen receptor levels were not associated with survival. These results suggest that measurement of cytosol progestin receptors is of prognostic value in advanced epithelial ovarian cancers.

Growth of mouse vaginal epithelial cells in culture: Functional integrity of the estrogen receptor system and failure of estrogen to induce proliferation

Normal mouse vaginal epithelial cells isolated from ovariectomized ca. 40-day-old BALB cCrg1 mice were purified by Percoll density gradient centrifugation and grown in primary culture using a collagen gel matrix and a serum-free complete medium. During the 9-day culture period, a 6-fold increase in cell number was observed. Addition of estrogen to the medium did not enhance epithelial cell proliferation. In fact, all doses of estrogen (180 fM to 18 nM) were inhibitory, resulting in only a 3- to 4-fold increase in cell number by day 9 of culture. Continuous exposure to estradiol (1.8 nM) for 9 days in the serum-free complete medium resulted in a decrease in cytosolic estrogen receptors with associated nuclear accumulation of estrogen receptors. A corresponding increase of cytosolic progestin receptors was also observed, indicating that no qualitative modification of the estrogen receptor system had occurred. Thus, despite its effectiveness in specific product synthesis (progestin receptors), estrogen does not stimulate proliferation of vaginal cells in this culture system, but rather inhibits epithelial cell proliferation.

Anisomycin inhibition of estradiol-induced and progesterone-facilitated luteinizing hormone surges in the immature rat.

These studies were designed to examine the effect of anisomycin, a potent and reversible inhibitor of protein synthesis with low systemic toxicity in rodents, on induction of luteinizing hormone (LH) surges by estradiol and their facilitation by progesterone. Immature female rats that received estradiol implants at 0900 h on Day 28 had LH surges approximately 32 h later (1700 h on Day 29). Insertion of progesterone capsules 24 h after estradiol led to premature (by 1400 h) and enhanced LH secretion. Protein synthesis was inhibited by 97%, 95%, 47%, and 16% in the hypothalamus-preoptic area (HPOA) and by 98%, 87%, 35%, and 0% in the pituitary at 30 min, 2 h, 4 h, and 6 h after s.c. injection of anisomycin (10 mg/kg BW), respectively. A single injection of anisomycin at 0, 3, 6, 9, 12, 24, 27, or 30 h after estradiol treatment significantly lowered serum LH levels at 32 h. The effect of injecting anisomycin at 0, 24, or 27 h was overridden by progesterone treatment at 24 h, but LH secretion was delayed serum LH levels were basal (10-30 ng/ml) at 1400 h but elevated (500-800 ng/ml) at 1700 h. Complete suppression of LH surges in estradiol-plus-progesterone-treated rats was achieved with 2 injections of anisomycin on Day 29 at 0900 h and again at 1200 h or 1400 h. Further experiments were designed to examine proteins that might be involved in anisomycin blockade of progesterone-facilitated LH surges. Intrapituitary LH concentrations at 1700 h on Day 29 were 70-80% higher (102 +/- 12.5 micrograms/pituitary) in rats that received 2 injections of anisomycin than in vehicle-treated controls (58.5 +/- 7.7 micrograms/pituitary). There were no significant effects of anisomycin on cytosol progestin receptors in the HPOA (7.1 +/- 1.5 fmol/tissue, anisomycin; 7.2 +/- 0.3, vehicle) or pituitary (8.3 +/- 1.3 fmol/tissue, anisomycin; 11.7 +/- 2.9, vehicle) at this time. The concentration of pituitary gonadotropin-releasing hormone receptors (GnRH-R), however, was significantly lower after anisomycin (265 +/- 30 vs. 365 +/- 37 fmol/mg protein) treatment. These results suggest that both estradiol-induced and progesterone-facilitated LH surges involve protein synthetic steps extending over many hours. Blockade of progesterone-facilitated LH surges by anisomycin appears to be due primarily to an effect on release of LH to which lowering of GnRH-R levels may contribute.

The α 1-noradrenergic antagonist prazosin decreases the concentration of estrogen receptors in female rat hypothalamus

A series of experiments was performed to determine the effects of the α 1-noradrenergic antagonist, prazosin, on the concentration of estrogen receptors in female rat brain and pituitary gland. Prazosin caused a dose-dependent decrease in the concentration of cytosol estrogen receptors in fediobasal hypothalamus when injected 10 and 16 h prior to assay. The drug was without effect on the concentration of nuclear estrogen receptors in the absence of estradiol, indicating that the decreased concentration of cytosol estrogen receptors is not due to nuclear estrogen receptor accumulation. Scatchard analysis confirmed that prazosin treatment decreases the conceptors of cytosol estrogen receptors without influencing the apparent affinity of the receptors for [ 3H]estradiol. The prazosin-induced decrease in the concentration of cytosol estrogen receptors in the mediobasal hypothalamus was transient with maximal effects occurring between 8 and 12 h after a single injection. Competition analysis confirmed that prazosin is not an effective competitor for binding to the estrogen receptor in vitro. The effects of prazosin on the estrogen receptor system could not be attributed to modulation of the levels of norepinephrine or dopamine. Assay of the levels of norepinephrine and dopamine in hypothalamus and preoptic area after prazosin injection revealed no effects of prazosin on the level of either of these catecholamines. An estradiol injection resulted in the predicted decrease in the concentration of estrogen receptors accumulating in hypothalamic cell nuclei, suggesting that the cytosol estrogen receptors that decrease in concentration are functional receptors. Prazosin treatment did not result in a decrease in the effectiveness of estradiol in the induction of cytosol progestin receptors in the mediobasal hypothalamus, suggesting that the cells are regulated by the α 1-noradrenergic system may not be those cells in which progestin receptors are also induced. These experiments provide further evidence that the noradrenergic system modulates the concentration of estrogen receptors, and perhaps sensitivity to estradiol, in some cells within the rat hypothalamus.

Modulation of steroid hormone receptors in the brain—inhibitory effect of fatty acids on the binding between cytosol progestin receptors in the rat cortex and R5020

The specific binding of R5020 to the 7S cortical progestin receptors was markedly inhibited by unsaturated long chain fatty acids, such as oleic acid, arachidonic acid, and docosahexaenoic acid. The inhibitory effect of docosahexaeonic acid was dose-dependent in the range of 1.5 × 10 −6 M to 1.5 × 10 −4 M.

Noradrenergic modulation of hypothalamic progestin receptors in female guinea pigs is specific to the ventromedial nucleus

The concentration of estrogen-induced cytosolic progestin receptors (CPRs) in the hypothalamus of α1-noradrenergic antagonist- treated female guinea pigs is reduced relative to non-drug-treated controls. The present study determined where within the hypothalamus this reduction occurs. Ovariectomized, estradiol-treated guinea pigs were given either the α1-noradrenergic antagonist prazosin or vehicle. Microdissected brain regions were assayed for CPR levels. Prazosin caused a selective relative decrease in CPR levels of the ventromedial nucleus of the hypothalamus. No significant effects of prazosin were seen in other hypothalamic or preoptic area nuclei.

Regulation of estrogen-stimulated lordosis behavior and hypothalamic progestin receptor induction by antiestrogens in female rats

Two estrogen antagonists, CI-628 (CI) and tamoxifen (TX), were used to examine the relationship between estrogen priming of lordosis behavior and progestin receptor induction in the hypothalamus-preoptic area (HPOA) of ovariectomized female rats. Lordosis behavior was assessed by measuring lordosis quotients (LQ) in response to injection of 2 μg of estradiol benzoate (EB) followed 48 hr later by 500 μg of progesterone (P). Behavior testing began 4 hr after P injection. The effects of antiestrogens were assessed by injecting CI and TX (1–2 mg) from 0 to 48 hr prior to EB. Levels of cytosol progestin receptor in the HPOA were determined by quantifying the specific binding of 0.5 n M [ 3H]R5020 to cytosols from animals receiving the same EB and antiestrogen treatments used in behavioral testing. TX given concurrently with or CI given 2 hr before EB abolished both lordosis behavior and induction of HPOA progestin receptors. In contrast, CI given 12 hr prior to EB abolished lordosis but permitted a 95% elevation in the concentration of progestin binding sites in the HPOA. TX or CI given 48 hr before EB resulted in moderate levels of lordosis (mean LQs from 56 to 69) and induction of HPOA progestin receptors from 85 to 130% above noninjected controls. However, CI given 24 hr prior to EB produced less than a 40% increase in brain R5020 binding even though lordosis behavior was equivalent to that seen in the 48-hr animals (mean LQ = 53). These data indicate that the effects of antiestrogens on female sexual behavior and on the synthesis of brain progestin receptors depend on which antiestrogen is used and the time interval between administration of estrogen and antiestrogen. They also demonstrate that under some conditions estrogen induction of cytosol progestin receptors in the HPOA can be dissociated from estrogen priming of lordosis behavior in rats.

Estrogen induction of progestin receptors in microdissected hypothalamic and limbic nuclei of female guinea pigs.

Estrogen induction of cytosolic progestin receptors (CPRs) in the hypothalamus-preoptic area of the female guinea pig is correlated with facilitation of female sexual behavior and gonadotropin secretion by progesterone. The present study validated a CPR microassay and determined where, within microdissected areas of the hypothalamus-preoptic area of the female guinea pig, induction of CPRs by estradiol occurs. Ovariectomized adult guinea pigs were given 20 micrograms estradiol benzoate (EB) or oil vehicle for 3 successive days. CPRs were measured using the synthetic progestin [3H]-R5020. The highest basal (no estrogen treatment) level of CPRs was seen in the arcuate-median eminence (34.1 +/- 3.7 fmol/mg). With EB treatment, the highest level of CPRs was again in the arcuate-median eminence (178.0 +/- 12.0 fmol/mg). EB-treated females also had high CPR levels in the periventricular area (88.5 +/- 10.8 fmol/mg) and the medial preoptic area (86.3 +/- 9.3 fmol/mg). Moderate levels were seen in the ventromedial nucleus of the hypothalamus (32.7 +/- 3.0 fmol/mg) and in the anterior hypothalamic nucleus (13.0 +/- 2.1 fmol/mg), but these were not significantly different from the low levels in the medial amygdala (4.5 +/- 1.2 fmol/mg) and in the dorsomedial nucleus of the hypothalamus (5.4 +/- 1.1 fmol/mg) of EB-treated females. However, EB caused a significant induction over baseline levels not only in the arcuate-median eminence, periventricular area, and medial preoptic area, but also in the ventromedial nucleus of the hypothalamus and the anterior hypothalamic nucleus. EB did not increase CPRs in the medial amygdala or the dorsomedial nucleus of the hypothalamus.

Estrogenic feminization of the LH response to orchidectomy: Association with prolonged nuclear estradiol receptor retention and induction of cytoplasmic progestin receptors in brain and pituitary

A sex difference in the LH rise after gonadectomy is clearly observable in the rat. While male rats respond with an early (10–12 h) increase in LH after orchidectomy, a delayed response (2–3 days) is recorded after ovariectomy. In this study we tested the hypothesis that the delayed response to gonadectomy in the E 2-treated males is due to a more prolonged retention of E 2 (when compared with the corresponding male feedback signal, testosterone) within specific central nuclear receptor sites. Orchidectomized (ORDX) animals implanted with either empty or E 2-filled Silastic capsules were sacrificed at 0, 24. 48 and 72 h after ORDX or E 2-capsule removal. LH levels in ORDX rats rose several-fold by 24 h, whereas E 2treated, ORDX rats. showed no changes in peripheral LH levels until 72 h after E 2-capsule removal. At the time of E 2-capsule removal (0 h) large increases in nuclear estradiol receptor (NER) levels were seen in anterior pituitary, preoptic area, and hypothalamus (HYP). Twenty-four hours after E 2-capsule removal. NER levels were still high in the 3 areas, and by 48 h NER values had returned to control (ORDX) levels, with the exception of HYP where they were slightly but significantly elevated. The increase in NER, as well as the subsequent decline after E 2-capsule removal was paralleled by similar changes in cytosolic progestin receptor (CPR) levels in all three regions. Cytosolic testosterone levels were not changed by the E 2-treatment. The results indicate that the feminized response to orchidectomy observed in E 2-implanted males is related to a prolonged retention of the E 2-receptor in nuclear sites. Further, they indicate that E 2-treatment in males, as is the case in females, can induce a marked increase in progestin receptor levels within specific brain regions as well as in the pituitary. The reduction in NER and CPR levels to castrate values precedes the first detectable increase in peripheral LH levels. In conclusion, the pattern of LH rise after gonadectomy in the rat is dependent upon the steroidal milieu at the time of removal of the gonads.

Estrogen-induced progestin receptors in the brain and pituitary of the South African clawed frog, Xenopus laevis.

High-affinity progestin binding sites were found in the brain and pituitary of the female South African clawed frog, Xenopus laevis. Cytosol progestin receptors in the hypothalamus-preoptic area and pituitary were increased in number by estradiol treatment in ovariectomized frogs. The telencephalon also contained high-affinity binding sites, but the concentration was not affected by estrogen priming. Autoradiographic analysis of the distribution of the synthetic progestin 3H-R5020 revealed some lightly labeled cells in the anterior preoptic area and ventral infundibulum of ovariectomized animals. After estrogen priming, many heavily labeled cells were observed in the following areas: ventrolateral striatum and amygdala, anterior preoptic area, ventral infundibular nucleus, laminar nucleus of the torus semicircularis, and anterior pituitary. The areas in which dense accumulations of 3H-R5020 labeled cells were found after estrogen treatment are a subset of areas known to contain estrogen binding sites. The induction of progestin receptors by estradiol may be related to the requirement for both estrogen and progestin to elicit female sexual behavior in this species.

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.

Loss of hypothalamic nuclear-bound progestin receptors: Factors involved and the relationship to heat termination in female guinea pigs

The hypothesis that the termination of sexual receptivity (heat) in female guinea pigs results from loss of progestin receptors from hypothalamic cell nuclei was tested. First, we attempted to find an optimal dose of progesterone that would result in a prolonged period of sexual receptivity. Ovariectomized guinea pigs were implanted with 10% estradiol capsules. Forty hours later, each received one of several sized progesterone capsules before being tested hourly for lordosis. Surprisingly, none of the progesterone doses resulted in delayed heat termination. In order to determine whether elevated levels of estradiol and progesterone maintain elevated levels of nuclear progestin receptors despite the lack of effect on heat duration, animals were treated as described above except that only one size progesterone capsule (3.0 cm) or an empty capsule was implanted. Despite elevated serum progesterone concentrations, nuclear progestin receptor levels decreased gradually and approached control levels at about the same time as heat termination had occured in similarly-treated animals. Cytosol progestin receptor levels decreased following progesterone treatment and remained lowered at all times measured. In order to further investigate the relationship between blood progesterone concentrations and retention of nuclear progestin receptors we decreased blood progesterone concentrations by removing progesterone capsules 2 h following insertion. Nuclear progestin receptor levels declined gradually concurrent with a decline in serum progesterone levels in animals exposed to progesterone capsules for only 2 h. In animals exposed to capsules continuously, nuclearprogestin receptor levels again decreased but at a slightly slower rate. In order to test the effect of progesterone capsule removal on female sexual behavior, ovariectomized guinea pigs were treated as described and tested hourly for lordosis. Fewer animals in the group exposed to progesterone capsules for 2 h became sexually receptive as compared to animals continuously-exposed to progesterone capsules. Of those animals that did respond, heat termination had occured by the same time that nuclear progestin receptor levels had returned to control levels in similarly-treated animals. These experiments support the hypothesis that heat termination results from the loss of progestin receptors from hypothalamic cell nuclei. In addition, they demonstrate that circulating progesterone levels play a role in regulating nuclear progestin receptor retention.

Effect of 5 alpha-dihydrotestosterone on sexual receptivity and neural progestin receptors in ovariectomized rats given pulsed estradiol.

Experiments were carried out to examine the mechanism whereby 5 alpha-dihydrotestosterone (DHT) antagonizes the stimulatory effects of estrogen plus progesterone (P) on sexual receptivity (lordosis) in the ovariectomized rat. Estradiol (E2; 1 microgram s.c. in 10% ethanol) was administered in a discontinuous (pulsed) treatment regimen thought to mimic phase requirements of estrogen action; two injections of E2 were given either 6 or 12 h apart (first injection, Hour 0). Progesterone (0.5 mg in oil) was injected at Hour 20, and behavioral testing occurred at Hour 24. Dihydrotestosterone (2.5 mg s.c. in 10% ethanol/propylene glycol) inhibited lordosis when it was given before (-12 or -3 h), between (+3, or -3 and +3 h), or after (+8 h) the two E2 injections, but was not effective when given at +20 h. Significant inhibition of E2 + P-induced lordosis was achieved by 2.5 but not 1.0 or 0.2 mg DHT at -3 h, while uterine weights in the same animals were reduced significantly by 2.5 and 1.0 mg DHT. Serum E2 and DHT concentrations peaked rapidly after injection, declining to near baseline by 3 and 12 h, respectively. Induction of cytosolic progestin receptors (cPR) in the preoptic area and medial basal hypothalamus by estrogen was not prevented by DHT when animals were given the two pulsed E2 injections or daily injections of estradiol benzoate, although P was able to override the inhibitory behavioral effects of DHT in the latter but not the former group.(ABSTRACT TRUNCATED AT 250 WORDS)