Nuclear Receptor Content Research Articles

An immunohistochemical study of estrogen and progesterone receptors in adenocarcinoma of the endometrium and in the adjacent mucosa.

The immunoperoxidase stain for estrogen and progesterone receptor content in endometrial adenocarcinoma was correlated with the grade and stage, level of myometrial invasion, age and survival of the patients. Anti-estrogen and anti-progesteone receptor monoclonal antibodies were applied to paraffin-embedded tissue from hysterectomy specimens of 100 patients with adenocarcinoma of the endometrium. In 34 of the cases the receptors were studied in the endometrium adjacent to the tumor and compared to the nuclear receptor content in the carcinoma. There was a high inverse correlation between the estrogen receptor status and the grade of tumor (R = - 0.45, P = 0.006). The estrogen receptor measured in the endometrium near the tumor showed a negative correlation with the grade of the tumor (R = -0.42, P = 0.013). The estrogen, but not the progesterone, receptor content, was positively related to the age of the patient (P < 0.05). No significant correlation of the receptor status with the depth of myometrial invasion was found, despite the obvious interdependence between the grade and myometrial invasion. The progesterone receptor staining index appeared to be a distinct independent prognostic factor in endometrial cancer. The immunohistochemical analysis of the steroid hormone status in endometrial cancer therefore offers an alternative to the quantitative ligand-binding assay.

Identification and changes in concentrations of prostaglandin H synthase (PGHS) isoforms in rat myometrium at parturition

The isoform(s) of prostaglandin H synthase (PGHS) present in pregnant rat myometrium have been identified and the ontogeny of their expression studied during late gestation and parturition. Concentrations of PGHS have been related to changes in concentration of nuclear and cytosolic estrogen (ER) and progesterone receptors (PR) occurring at this time. Nuclear PR concentrations were maximal on days 16–18 of pregnancy, decreased from days 18 to 22 (delivery) and fell 24 hours postpartum. Nuclear ER concentrations increased significantly from days 20 to 22 of pregnancy and fell postpartum. Whereas the ratio of nuclear ER/PR was firmly in favour of progesterone action on days 16–20 it increased on day 22 corresponding to increased estrogen action. Western immunoblotting with specific antibodies revealed a single 72 kDa PGHS-1 isoform in myometrium at each timepoint. There was no evidence for the inducible PGHS-2 isoform in myometrium. Densitometric analysis showed the concentration of PGHS-1 increased significantly from day 16 to a maximum at the time of delivery on day 22 and decreased immediately afterwards. Expression of the constitutive PGHS-1 isoform is associated with the changing ratio of nuclear ER/PR and may therefore be hormonally regulated.

The influence of vasectomy and vasovasostomy on testicular ATPases, cAMP, ABP and androgen receptor in rabbits

The present study was performed to further clarify the influences of vasectomy on functions of testis and to disclose the possible mechanisms of infertility after vasovasostomy (VV). Thirty-one rabbits were divided into sham-operated control group (C), vasectomy control group (V), VV fertility group (VaF) and VV infertility group (Val). Serum testosterone (ST) level, testicular cAMP, androgen binding protein (ABP), nuclear androgen receptor (NAR) concentrations, testis cell membrane Na +−, K +− ATPase, Mg 2+− ATPase activities, sperm density and testis weight were measured. Vasectomy resulted in significantly reduced cAMP, Na +−,K +−ATPase, Mg 2+− ATPase, testis weight and increased ABP; VV completely restore testis weight in VaF and Val, Na +−, K +− ATPase, Mg 2+− ATPase in VaF, partly cAMP in VaF and Val, Na +−, K +− ATPase, Mg 2+− ATPase in Val, but did not restore ABP. The NAR content in Val was significantly lower than those in C, VaF and V. No statistical differences among 4 groups were seen in Kd values for [ 3H]-T. ST levels in VaF, Val and V were insignificantly different compared with C, but the value in VaF was higher than that in Val (p < 0.05). Sperm density after VV reached 122 ± 62 × 10 6/ml in VaF and 10 ± 24 × 10 6/ml in Val, both in VaF and Val were, significantly low compared with C (p < 0.001), and the value in Val was remarkedly lower than that in VaF (p < 0.001). It was shown that sperm density was positively correlated with cAMP content, Na +−, K +−, ATPase, Mg 2+− ATPase activities, but negatively with ABP. These results suggest that vasectomy gives rise to damage to the testis, and vasovasostomy does not appear completely effective in reversing testicular changes.

Changes in the density of nuclear estrogen receptors in urogenital tissue during pseudopregnancy in the rabbit

To elucidate the possible role of progesterone in pregnancy-induced urinary incontinence, the concentration of nuclear estrogen receptors (E2R) was measured in the urogenital tissues of non-pregnant (controls) and on days 6, 12 and 18 of pseudopregnancy in the rabbit. Whereas in the uterus E2R levels decreased by at least five-fold by day 6 of pseudopregnancy, changed little through day 12 and increased again at day 18, in the vagina and urethra only a small and insignificant decrease and increase occurred at days 6–12 and day 18, respectively. The receptor affinity, as judged by the computed KD values, did not change significantly in any of the preparation during pseudopregnancy. Similar changes in the E2R density were observed in rabbits treated with progesterone. These data provide further and concrete evidence for the tissue specificity in the downregulation of E2R by progesterone.

Analysis of hypothalamo-hypophyseo-gonadal relationships in female rats with experimental diabetes

Hypothalamo-hypophyseo-gonadal system functional activity was studied in rats with streptozotocin diabetes. In intact rats concentrations of sex hormones nuclear receptors were measured in the hypothalamic preopticoanterior, mediobasal segments and in the adenohypophysis, as were blood serum gonadotropins and sex hormones. Estradiol and progesterone were injected to ovariectomized females and LH-RH levels measured in preopticoanterior segment of the hypothalamus, arcuate nucleus, and median eminence, as well as LH and FSH concentrations in the blood in order to detect disorders in basal and cyclic gonadotropin secretion. Streptozotocin injection to cycling females disordered the estral cycle and was associated with reduction of LH, FSH, and sex hormones basal and cyclic secretion. Estradiol nuclear receptors concentrations reduced in the preopticoanterior hypothalamus and hypophysis, the count of nuclear testosterone-binding sites reduced only in the hypophysis. Gonadotropin wave stimulated with sex steroids in ovariectomized females was reduced in diabetes because of changed activity of LH-RH-producing system. We believe that changes in basal and cyclic secretion of gonadotropins in rat females with experimental diabetes is explained by reduced activity of LH-RH-producing system and receptor binding at the level of the hypothalamo-hypophyseal complex.

Image analysis of androgen receptor immunostaining in metastatic prostate cancer heterogeneity as a predictor of response to hormonal therapy

Reliable predictors of the response of prostate cancer to androgen ablation therapy are lacking. The goals of this study were to determine whether nuclear androgen receptor (AR) concentrations in metastatic prostate cancer varied within and between specimens and to correlate this information with the response to therapy. AR concentration was evaluated by computer-assisted image analysis of immunohistochemical staining intensity in 200 malignant epithelial nuclei of each of 17 specimens of Stage D2 prostate cancer obtained before hormonal therapy. The data were correlated with the time to tumor progression (relapse) after hormonal therapy. AR staining intensity varied within specimens, and the variance of staining intensity was significantly greater (P = 0.03) in the poor responders (n = 8; time to progression, < 20 months) than in the good responders (n = 9; time to progression, > or = 20 months). The kurtosis was significantly lower in poor responders (P = 0.04). However, the mean AR staining intensity was not significantly different among patients. The frequency distribution plots of good responders were generally uniform and unimodal, but those of poor responders were flattened (more platykurtic), dispersed, and highly variable. Thus, the AR concentration per cell was significantly more heterogeneous in poor responders. Variance was a significant predictor of response. Five of 6 patients with a high variance (defined as variance greater than the mean) were poor responders, whereas 8 of 11 patients with a low variance were good responders (an overall classification accuracy of 13 of 17, 76%). The greater AR heterogeneity in poor responders may reflect a greater genetic instability in tumors that have progressed further toward androgen independence and may be a valuable predictor of progression.

Aromatase activity in the rat brain: Hormonal regulation and sex differences

The intracellular conversion of testosterone to estradiol by the aromatase enzyme complex is an important step in many of the central actions of testosterone. In rats, estrogen given alone, or in combination with dihydrotestosterone, mimics most of the behavioral effects of testosterone, whereas treatment with antiestrogens or aromatase inhibitors block facilitation of copulatory behavior by testosterone. We used a highly sensitive in vitro radiometric assay to analyze the distribution and regulation of brain aromatase activity. Studies using micropunch dissections revealed that the highest levels of aromatase activity are found in an interconnected group of sexually dimorphic nuclei which constitutes a neural circuit important in the control of male sexual behavior. Androgen regulated aromatase activity in many diencephalic nucleic, including the medial preoptic nucleus, but not in the medial and cortical nuclei of the amygdala. Additional genetic evidence for both androgen-dependent and -independent control of brain AA was obtained by studies of androgen-insensitive testicular-feminized rats. These observations suggest that critical differences in enzyme responsiveness are present in different brain areas. Within several nuclei, sex differences in aromatase induction correlated with differences in nuclear androgen receptor concentrations suggesting that neural responsiveness to testosterone is sexually differentiated. Estradiol and dihydrotestosterone acted synergistically to regulate aromatase activity in the preoptic area. In addition, time-course studies showed that estrogen treatment increased the duration of nuclear androgen receptor occupation in the preoptic area of male rats treated with dihydrotestosterone. These results suggest possible ways that estrogens and androgens may interact at the cellular level to regulate neural function and behavior.

The hypophyseogonadal system of male rats with diabetes: an experimental study

The hypophyseogonadal system of male rats with streptozotocin-induced diabetes was studied. The hypophyseal sensitivity to LH releasing hormone was analyzed in vitro and concentrations of sex hormone nuclear receptors in the adenohypophysis, participating in gonadotropin secretion regulation according to a negative feedback mechanism, measured. Streptozotocin injection reduced blood testosterone concentration and levels of androgen nuclear receptors in the rat hypophysis. Blood LH and FSH levels in the rats with diabetes were virtually the same as in intact animals. In vitro experiments have demonstrated that diabetes development in rats did not influence the level of LH basal secretion by the hypophysis. The maximal response to LH releasing hormone was recorded in the control males in 3h incubation, whereas the rate of LH secretion in the experimental animals did not differ from the normal one. The authors suggest that changed mechanism of the hypothalamo-hypophyseo-gonadal system regulation in experimental diabetes is related to the hypophyseal disorders, involving reduction of the LH-RH-stimulated gonadotropin release and of the testosterone receptor levels, this resulting in poor reproductive function control according to the negative feedback principle.

Estrogen Responsiveness of Vitellogenin Gene Expression in Rainbow Trout (Oncorhynchus mykiss) Kept at Different Temperatures

We have examined the effect of ambient water temperature on the ability of juvenile rainbow trout to respond to estradiol (E2) injection with vitellogenin (Vg) synthesis. Vg appeared in serum within 24 hr of E2 injection in fish kept at 15° and rose to 70 mg/ml over a 10-day treatment period during which four injections of E2 were given. A group of fish kept at 9° responded more slowly to the same multiple injection protocol and showed Vg accumulation of only 8.9 mg/ml on the 10th day. Hepatic Vg mRNA levels accumulated more rapidly and extensively in animals treated and kept at 15° than at 9°; however, differences in serum Vg concentrations could not simply be attributed to differences in Vg mRNA levels. The ratio of serum Vg:Vg mRNA increased steadily over the treatment period, especially in the 15° group, suggesting greater efficiency or capacity for translation and/or processing of the Vg protein at the higher temperature. Examination of hepatic nuclear estrogen receptor (ER) concentrations revealed a three- to five-fold increase in high-affinity E2-binding activity within the first 24 hr after injection in both temperature groups. Nuclear ER levels remained elevated to roughly the same extent in both groups throughout the 10-day period. Differences in nuclear ER concentrations and serum E2 concentrations could not account for the large differences in Vg mRNA and protein levels between the two temperature groups. Furthermore, a single injection of E2 at 15° was able to induce higher levels of Vg mRNA and protein than multiple injections at 9°. We suggest that temperature modulates the responsiveness of the liver to E2 at stages which are independent of E2 or ER concentrations.

Effect of Estrogen Treatment on the Peroxidase Activity and Estrogen Receptors in the Female Rabbit Urogenital Tissues

The effect of one, 4 and 8 weeks of continuous estrogenization of rabbit on peroxidase (PO) activity and on both cytplasmic and nuclear estrogen receptors was studied in the uterus, vagina, urethra and urinary bladder. Whereas the peroxidase activity in the urogenital tissue of untreated controls was near zero, after one week of estrogen treatment it increased very substantially in the uterus and vagina and much less dramatically in the urethra or urinary bladder. With continuation of estrogen treatment for 4 or 8 weeks the PO decreased by 80–90% in the uterus and vagina and by only 40% in the urethra. After one week of estrogen treatment the density of both cytosolic and nuclear estrogen receptors decreased by several fold in both the uterus and vagina, whereas it decreased by 30–50% in the urethra and bladder. The concentration of both cytosolic and nuclear receptors decreased further although less dramatically with continuing estrogen treatment, up to 8 weeks, in all tissues. These data suggest that although the general pattern of responses to estrogen showing an initial increase in PO followed by a reduction with continuing estrogen treatment is the same in all urogenital tissues, the responses seem to have a prolonged time scale in the case of lower urinary tract tissues. The quantitative aspect of the response generally corresponds with the density of estrogen receptors in the urogenital tissues.

Phorbol esters inhibit the dioxin receptor-mediated transcriptional activation of the mouse Cyp1a-1 and Cyp1a-2 genes by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Tetradecanoyl phorbol acetate (TPA) has been shown to inhibit 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced mouse P450IA1 benzo[a]pyrene hydroxylase activity (Raunio, H., and Pelkonen, O. (1983) Cancer Res. 43, 782-786). When we co-administered TPA and TCDD to C57BL/6 mice, the accumulation of TCDD-inducible liver P450IA1 and P450IA2 mRNA, as well as kidney P450IA1 mRNA, was greatly inhibited. When nuclear run-on assays were conducted, maximal levels of transcriptional activation were achieved for both liver Cyp1a-1 and Cyp1a-2 with 1 micrograms/kg (approximately equal to 3.0 nmol/kg) TCDD. TCDD elicited a dose-dependent increase in the rates of gene transcription, which paralleled the induction of P450IA1 and P450IA2 mRNA. Only Cyp1a-1 gene transcription was elevated in kidney. When these experiments were repeated following the co-administration of TPA with TCDD, the levels of TCDD-mediated transcriptional increases in liver Cyp1a-1 and Cyp1a-2 and P450IA1 and P450IA2 mRNAs were dramatically inhibited. The reduction in Cyp1a gene transcription by TPA could be accounted for by reduced DNA binding of the dioxin receptor to the xenobiotic-responsive element (XRE) sequences, as measured by gel-retardation analysis. Analysis of nuclear [3H]TCDD dioxin receptor by sucrose density gradients demonstrated that the inhibition of Cyp1a gene transcription and DNA binding by TPA resulted from a reduction in nuclear dioxin receptor concentration.

Androgen‐Dependent and ‐Independent Aromatase Activity Coexists with Androgen Receptors in Male Guinea‐Pig Brain

Abstract Using a microdissection technique we localized androgen receptors and aromatase activity (AA) in the brain of male guinea-pigs. In addition, we evaluated the effects of castration and androgen replacement on androgen receptor dynamics and induction of AA. In the castrate animal, cytosolic androgen receptor content was highest in the basal hypothalamus, specifically in the median eminence-arcuate nucleus (> 15 fmol mg protein (1)), while lesser levels were found in the preoptic regions and amygdala. Nuclear receptor content was highest (> 150 fmol mg DNA (-1)) in the median eminence-arcuate nucleus, periventricular region of the preoptic area and cortical amygdala. All regions investigated showed a significant decrease in nuclear receptors following castration and an increase with androgen replacement. However, reciprocal changes in cytosolic androgen receptors were not always evident. Aromatase activity was high in the cortical amygdala, medial amygdala, periventricular region of the preoptic area and bed nucleus of the stria terminalis. Castration and androgen replacement had significant stimulatory effects on AA in the ventral medial hypothalamus, median eminence-arcuate nucleus, cortical amygdala and periventricular regions of the preoptic area and anterior hypothalamus. Thus, androgen receptors and AA are unevenly distributed throughout the subcortical regions of the male guinea-pig brain and respond differently to endocrine stimuli. Our data demonstrate that AA is androgen-dependent in some subcortical regions which contain androgen receptors. Even though nuclear receptors in all brain regions were affected by castration and dihydrotestosterone treatment, the events were not always linked to AA regulation. Due to this difference in regulation, AA may serve divergent functions in guinea-pig brain.

Nuclear estrogen receptor binding in microdissected brain regions of female rats during pregnancy: Implications for maternal and sexual behavior

Previously, we showed that changes in nuclear estrogen receptor (NER) concentrations within large dissections of the preoptic area and hypothalamus of pregnant rats might underlie changes in both maternal and sexual behaviors. To more precisely localize these biochemical changes, NER concentrations were measured in microdissected nuclei within the preoptic area and hypothalamus of pregnant rats on days 8, 16 and 22. Results indicated that NER levels changed significantly throughout pregnancy and that the magnitude and direction of change was site specific. Although a different pattern of change was found in each nucleus, NER levels in most preoptic area nuclei were significantly higher by the 16th day of pregnancy compared to those on day 8, while receptor levels in most hypothalamic nuclei did not increase until day 22 of pregnancy. The higher NER levels found in preoptic area nuclei of female rats as pregnancy advances can be correlated with growing maternal responsiveness during pregnancy, while elevated concentrations of NER in hypothalamic nuclei at the end of pregnancy may indicate preparation for postpartum estrus.

Decreased estradiol receptor concentrations in ethionine-induced fatty liver of rats

Ethionine, a methionine analogue, induces fatty liver in rats. The mechanism by which ethionine induces fatty liver is thought to be due to the inhibition of synthesis of very-low-density lipoprotein. Since the synthesis of lipoprotein is correlated with liver estradiol receptor concentrations, we examined the effect of ethionine on estradiol receptor concentrations in rat liver. Estradiol receptor concentrations in both cytosolic and nuclear fractions were greatly decreased by a single injection of ethionine at a dose of 0.5 mg g body wt. In particular, the decrease in nuclear receptor concentrations was observed a few hours after the injection and correlated with the decrease in triglyceride content in the very-low-density lipoprotein fraction. These results suggest that liver estradiol receptor is involved in the pathogenesis of ethionine-induced fatty liver of rats.

Effect of clomiphene citrate treatment on endometrial estrogen and progesterone receptor induction in women

A direct adverse effect of clomiphene citrate on the endometrium has been presumed, and interference with estrogen receptor-mediated endometrial estrogen receptor and progesterone receptor induction has been implicated as the mechanism responsible for an increased incidence of luteal phase deficiency in association with clomiphene citrate treatment. To clarify the net influence of clomiphene administration on endometrial steroid receptor induction, we studied five normal ovulatory women, in both a spontaneous and clomiphene-induced (150 mg/day, cycle days 5 to 9) ovulatory cycle. From cycle day 11 blood samples were obtained daily and urinary luteinizing hormone determinations were performed twice daily. Endometrial biopsy was performed on the day of the urinary luteinizing hormone surge and again 13 days after the surge. Serum levels of follicle-stimulating hormone and luteinizing hormone were determined by immunoradiometric assay, estradiol and progesterone by radioimmunoassay, and clomiphene citrate isomer concentrations in treatment cycles by reversed-phase high-performance liquid chromatography and fluorescence detection. Total, cytosolic, and salt-extracted nuclear endometrial estrogen receptor and progesterone receptor concentrations were determined by enzyme-linked immunoassay. Serum estradiol was threefold to fivefold higher (p less than 0.05) in clomiphene-induced than in spontaneous cycles 8 and 10 days before the luteinizing hormone surge, and progesterone was increased (p less than 0.05) from the day of the surge to end of the cycle. Serum enclomiphene rose to plateau between 12 and 6 days before the luteinizing hormone surge (4.1 +/- 0.8 ng/ml, mean +/- SE, n = 19) and fell thereafter to less than 1.0 ng/ml. Zuclomiphene levels increased rapidly between 14 and 8 days before the surge (53.9 +/- 2.8 ng/ml, mean +/- SE, n = 5) and then decreased gradually but remained elevated throughout the luteal phase (29.0 +/- 1.2 ng/ml, mean +/- SE, n = 33). Late luteal endometrial histology was abnormal in one of four available treatment cycle specimens, but the endocrine characteristics and number and subcellular distribution of estrogen receptor and progesterone receptor in the abnormal cycle were not different from those of normal, in-phase cycles.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of thromboxane receptor antagonists on oestrogen-induced uterotrophic responses in the spontaneously hypertensive rat

1. The possible role of thromboxane in the uterotrophic response to oestrogen, in the spontaneously hypertensive rat was investigated by use of the thromboxane receptor antagonists EP092, AH23848 and BM 13.505. 2. The parameters studied were uterine blood flow (measured by the microsphere technique), uterine wet and dry weights and the concentrations of cytosolic and nuclear oestrogen receptors. 3. The antagonists attenuated oestradiol-induced uterine blood flow and significantly reduced both wet and dry uterine weight. These changes were accompanied by decreases in nuclear oestrogen receptor levels. 4. The results suggest a supportive role for thromboxane in oestradiol-induced uterine growth.

Modification of the rat uterine response to oestrogen and tamoxifen by thromboxane antagonists.

1. The thromboxane receptor antagonists EP092, AH23848 and BM 13.505 were used to investigate the role of thromboxane in the uterotrophic response to oestradiol and tamoxifen. 2. The parameters examined were uterine blood flow (measured by the microsphere technique), uterine wet and dry weights and the concentrations of cytosolic and nuclear oestrogen receptors. 3. Only EP092 potentiated the hyperaemic response to oestrogen but all three thromboxane antagonists inhibited oestradiol-stimulated uterine growth. This inhibition was accompanied by a decrease in nuclear oestrogen receptor concentration. 4. The uterotrophic response to tamoxifen was unaffected by the thromboxane antagonists. 5. The mechanism by which the thromboxane antagonists may be exerting their growth inhibitory effect is discussed, although, whether this effect can be attributed to blockade of thromboxane receptors or to some other mechanism is not clear from this study.

Concentrations of Nuclear Progesterone Receptors in Endometrium of Virgin and Repeat Breeder Heifers after Embryo Transfer

The present study aimed to correlate the repeat breeder syndrome in the bovine with an impaired or suboptimal uterine progestational response. Concentrations of nuclear (i.e. transformed) receptors for progesterone (PRn) were determined with a binding and exchange method in endometrial samples from virgin (VH) and repeat breeder (RBH) heifers 15 days post oestrus. The heifers were recipients of Day 7 demi-embryos collected from donors with normal fertility and transferred 8 days prior to tissue sampling. Results were compared with both the type of heifer, the condition of the embryo present within the uterus and the temporal relationship to the hormone plasma levels. The binding data for PRn indicated that a single class of high-affinity, low-capacity sites existed. The amount of PRn in VH endometria holding embryonic structures was significantly greater than in RBH, but no statistical differences were found in their plasma progesterone levels. PRn concentrations were also higher in the uterine horn in which an elongated (greater than 15 mm), morphologically normal embryo was present, when compared to cornua with small (less than 5 mm) embryos, regardless of recipient group. Furthermore, in endometria with an elongated embryo in the lumen, the relative amount of PRn was significantly greater in VH than in RBH. The present results indicate that the RBH recipients of Day 7 demi-embryos by Day 15 have fewer numbers of specific receptors for maternal progesterone, which could explain in part the poorer development of the transferred embryos compared with that in virgin heifers.

Synergistic Induction of Aromatase Activity in the Rat Brain by Estradiol and 5α-Dihydrotestosterone

Estrogens are produced locally from androgen precursors by cells within the hypothalamus and preoptic area (POA). The activity of the aromatase enzyme complex responsible for this intracellular conversion is controlled by gonadal steroids. The purpose of this study was to determine: (1) whether estrogen acts together with androgen to regulate aromatase activity (AA) and (2) whether nuclear androgen receptor levels are increased after exposure to combined treatment with estradiol benzoate (EB) and dihydrotestosterone (DHT). Thus, adult male rats were castrated and treated for 1 week with either vehicle (0.1 ml sesame oil, s.c.), EB (2 micrograms/day), testosterone (3-cm Silastic implant), DHT (3-cm Silastic implant) or EB + DHT. These treatments produced hormone levels in the physiologic range. We found that both testosterone and DHT significantly stimulated AA (p less than 0.05 vs. castrated rats). However, testosterone induced AA significantly more than DHT in the POA (p less than 0.05; castrated + testosterone vs. castrated + DHT). EB alone did not affect AA but synergized with DHT to stimulate AA in the POA to levels equivalent with the testosterone-treated group. By comparison, EB alone did not enhance the induction of AA by DHT in the hypothalamus. Combined treatment with EB and DHT had no effect on the concentrations of nuclear androgen receptors in either tissue suggesting that the effect of EB was not mediated through an androgen receptor mechanism. These results suggest that both androgens and estrogens play a physiologic role in the control of estrogen formation in the rat brain. Furthermore, the anatomical specificity that we observed indicates that critical differences in enzyme responsiveness are present in different areas of the brain.

Developmental and thyroidal regulation of the nuclear T3 receptors/c-erb A oncogene products in the Ob 17 preadipocyte cell line.

In a thyroid hormone-sensitive mouse preadipocyte cell line (Ob 17), the concentration of nuclear T3 receptors increases during differentiation in an insulin-independent manner and decreases by 50-60 p.cent after medium supplementation with physiological concentrations of T3. The down-regulation of T3 receptors implies both quantitative and qualitative changes. The preadipocyte T3 receptors were previously reported to be heterogeneous in gel filtration and in their reactivity towards rabbit antibodies raised against large erb A alpha peptides. This report shows that the receptor heterogeneity is not modified during cell development, whereas T3 mainly depletes the receptor species that are both the most retarded in gel filtration and preferentially recognized by c-erb A alpha-specific antisera. The c-erb A alpha-related T3 receptors which predominate in preadipocytes, are thus probably mainly involved in receptor depletion by T3. A similar T3 receptor half-life of 12-13 h was estimated after cycloheximide addition to cells at confluence or later in the differentiation phase with or without T3. This suggested that development, or T3, might have mainly affected the production of T3 receptors. In Northern hybridization studies, using alpha- or beta-type c-erb A cDNA probes containing the entire coding sequence, only alpha-type mRNAs were detected with a predominant band of 2.8 kbases and two fainter bands of about 5.5 and 6.0 kbases. The alpha-type mRNA abundance relative to beta-actin significantly increased during differentiation and decreased after T3 addition.