Comparison of in vitro effects of the pure antiandrogens OH-flutamide, Casodex, and nilutamide on androgen-sensitive parameters

OBJECTIVES: A combination of flutamide (Eulexin) or nilutamide (Anandron) with a luteinizing hormone-releasing hormone (LHRH) agonist or orchiectomy is the only therapy demonstrated to prolong life in prostate cancer. Recently, the low 50-mg daily dose of Casodex, an analogue of the pure antiandrogen flutamide, was chosen for clinical studies on the basis that the compound was 5 to 10 times more potent than flutamide, as suggested by data obtained in the inappropriate intact rat model. The present study was designed to compare the in vitro antiandrogenic activity of OH-flutamide (OH-FLU), the active metabolite of flutamide, Casodex, and nilutamide. METHODS: The effect of the antiandrogens was tested on two androgen-sensitive parameters, namely proliferation of the SEM-107 clone of Shionogi mouse mammary tumor cells and secretion of the GCDFP-15 (gross cystic disease fluid protein 15 kDa) in T-47D and ZR-75-1 human breast cancer cells. RESULTS: The twofold stimulation of Shionogi cell proliferation caused by a 10-day exposure to 1 nM testosterone was competitively reversed by incubation with OH-FLU, Casodex, or nilutamide, at the respective IC50 values of 72, 243, and 412 nM. Moreover, the marked increase in GCDFP-15 release induced by 1 nM testosterone was blocked by OH-FLU. Casodex, or nilutamide at respective IC50 values of 29, 180, and 87 nM in T-47D cells and at 35, 142, and 75 nM in ZR-75-1 cells. Similar data were detected in 4-androstenedione-induced Shionogi cell proliferation and in dihydrotestosterone-induced GCDFP-15 secretion in T-47D cells. CONCLUSIONS: OH-FLU is 3.1- to 7.8-fold more potent than Casodex, as measured on two in vitro androgen-sensitive parameters, in agreement with our recent in vivo data obtained in the model of castrated rats supplemented with 4-androstenedione implants, in which threefold greater potency of flutamide was observed. The present data, as well as other data from the literature, strongly indicate the need to choose a more appropriate dose of Casodex for the treatment of prostate cancer.     

Prostate-sparing effects in primates of the potent androgen 7alpha-methyl-19-nortestosterone: a potential alternative to testosterone for androgen replacement and male contraception

7alpha-Methyl-19-nortestosterone (MENT) is a potent synthetic androgen that cannot be converted to dihydrotestosterone. In this study we determined the relative androgenic, antigonadotropic, and anabolic potencies of testosterone vs. MENT in the nonhuman primate M. fascicularis. In castrated monkeys, dose-response relationships were generated for the effects of testosterone and MENT on gonadotropin levels, prostate growth, body weight, and lipid metabolism. In a pilot study, four monkeys were castrated, and magnetic resonance imaging (MRI) was used to document a 50% loss of prostate volume within 8 weeks, verifying that MRI is a reliable means to measure prostate size in this species. Two additional groups of six monkeys each were then castrated and serially administered four graded dosages of testosterone or MENT via osmotic minipumps over 20 weeks. Complete suppression of LH was achieved with a minimum of 0.3 mg/day MENT, compared to 3.0 mg/day testosterone. MENT supported body weight 10 times more potently than did testosterone. Baseline prostate volumes were maintained with 0.1-0.2 mg/day MENT vs. 0.3 mg/day testosterone. Thus, in monkeys, MENT is 10 times more potent than testosterone with regard to the clinically desirable end points of gonadotropin suppression and anabolism, but only twice as potent at stimulating prostate growth. These results suggest that MENT may have a wider therapeutic index than testosterone for human androgen replacement and male contraception.     

Prognostic significance of tumour markers in endometrial cancer

BACKGROUND: Steroid 5 alpha-reductase is implicated in the pathogenesis of benign prostatic hyperplasia (BPH). We studied the in vitro and in vivo effects of FR146687, a new inhibitor of 5 alpha-reductase. METHODS: Two isozymes of rat and human 5 alpha-reductases were expressed in 293 cells. In vivo effects of drugs were evaluated on rat and dog prostates. Castrated immature rats were injected with testosterone propionate (TP) or 5 alpha-dihydrotestosterone propionate (DHTP) to induce growth of the ventral prostates. Testosterone and 5 alpha-dihydrotestosterone (DHT) contents in rat and dog prostates were measured by gas chromatography-mass spectrophotometry (GC-MS). RESULTS: FR146687 showed noncompetitive inhibition in both isozymes and no inhibitory effects on other steroid oxidoreductases. In mature rats and castrated immature rats treated with TP, FR146687 dose-dependently reduced ventral prostate and seminal vesicle weight at doses above 0.1 mg/kg, while castrated immature rats treated with DHTP were not affected by FR146687. FR146687 showed more potent reduction of rat prostates than finasteride. DHT concentration in the prostates was significantly reduced when FR146687 was administered to rats and beagles. CONCLUSIONS: FR146687 is a dual inhibitor for 5 alpha-reductase isozymes and significantly reduced the growth and DHT content in the prostate.     

Testosterone acts directly at the pituitary to regulate gonadotropin-releasing hormone-induced calcium signals in male rat gonadotropes

We have recently shown that castration alters GnRH-induced calcium (Ca2+) signaling in the gonadotropes of male rats. Instead of generating spike-plateau Ca2+ responses to high concentrations of GnRH (100 nM), the majority of gonadotropes from castrated rats have oscillatory Ca2+ responses, which are generally only seen with low concentrations of GnRH in the gonadotropes of intact rats. This change in the nature of GnRH-induced Ca2+ responses is prevented by in vivo testosterone treatment. The aims of the present study were, therefore, to determine if testosterone acts directly at the pituitary or via the regulation of hypothalamic GnRH secretion. Accordingly, castrated male rats were treated with a GnRH antagonist to ablate the effects of increased GnRH secretion at the pituitary gland. GnRH antagonist treatment (10 microg/100 g BW, twice daily for 7 days from the time of castration) decreased the concentration of LH in the serum of castrated rats (0.4 +/- 0.1 ng/ml vs. 11.2 +/- 0.4 ng/ml in untreated castrated rats, mean +/- SEM) but had no effect on the proportion of gonadotropes having oscillatory Ca2+ responses to 100 nM GnRH when compared with untreated castrated rats (63% in antagonist-treated castrated rats vs. 70% in untreated castrated rats). The GnRH antagonist treatment did not, however, interfere with the ability of in vivo testosterone treatment (100 microg/100 g body weight/day) to decrease the proportion of gonadotropes having oscillatory Ca2+ responses to 100 nM GnRH (26% in testosterone-treated rats vs. 25% in testosterone and antagonist-treated rats). These findings indicate that testosterone acts directly at the pituitary, and not by altered GnRH secretion, to modulate GnRH-induced Ca2+ signals. To confirm this suggestion, cultured gonadotropes of castrated male rats were treated in vitro with 10 nM testosterone. Testosterone treatment for twelve, but not 4 h, restored the proportion of gonadotropes having oscillatory Ca2+ responses to that seen in gonadotropes from intact rats. The in vitro effects of testosterone over 12 h were prevented by concomitant treatment with the protein synthesis inhibitor cycloheximide (10 microM), which, when given alone, had no effect on GnRH-induced Ca2+ signals in cells from castrate male rats. Taken together, these findings suggest that testosterone has a direct genomic action at the pituitary to regulate GnRH-induced Ca2+ signals, via a process that involves new protein synthesis.     

Society for Pediatric Research Presidential Address 1997: multiculturalism in research

OBJECTIVES: Because the large increase in luteinizing hormone secretion induced by flutamide in the intact rat is not found in men, we have used castrated rats and mice supplemented with androstenedione (4-dione) instead of intact animals to measure the activity of the pure antiandrogens flutamide and Casodex. METHODS: We first compared the effect of different schedules of administration of various doses of the two antiandrogens on prostate and seminal vesicle weights in the castrated rat and mice models. RESULTS: For both flutamide and Casodex, no consistent difference was found between the effects of once daily and thrice daily oral dosing in the rat. It was observed, however, that flutamide, especially at the high and therapeutically more effective doses, is about three times more potent than Casodex under both schedules of dosing. When flutamide was administered subcutaneously three times a day, twice a day, once a day, or once every second day in rats and mice, no difference was observed in the degree of inhibition achieved on prostate and seminal vesicle weights. CONCLUSIONS: The present data show that Casodex is about three times less potent than flutamide on the well-recognized parameters of androgen responsiveness in the rat, namely prostate and seminal vesicle weights. Another finding is that once daily dosing with flutamide exhibits an effectiveness comparable to thrice daily dosing; such data may have potential significance in facilitating compliance by administration of flutamide once daily instead of the current thrice daily schedule in men. Moreover, these data, if obtained in a reliable in vivo model, should be helpful in determining the choice of an appropriate dose of Casodex for the treatment of prostate cancer.     

The androgenic regulation of prostate proteins with a high affinity for deoxyribonucleic acid. Evidence for a prostate deoxyribonucleic acid-unwinding protein

1. When testosterone is injected into castrated rats in vivo, a significant increase in the incorporation of [35S]methionine into prostate proteins may be detected under conditions in vitro. 2. Studies based on DNA-cellulose chromatography show that the synthesis of prostate proteins with a high affinity for DNA is particularly enhanced by androgenic stimulation. 3. These changes in protein synthesis are negated when the anti-androgen, cyproterone acetate, is administered concomitantly with testosterone in vivo. 4. Two assays were developed for measuring the strand separation of prostate DNA; first, the retention of 3H-labelled native DNA on nitrocellulose membranes, and second, the activation of native DNA as a template for 9S prostate DNA polymerase. On the basis of these criteria, DNA-unwinding activity is present in the prostate gland and it is regulated by androgens in a steroid-and tissue-specific manner. 5. The results are discussed in the context of the mechanism of action of androgens, particularly since the changes provoked in DNA-unwinding activity by androgens precede the onset of DNA replication and mitosis.     

Effects of hypophysectomy and prolactin replacement therapy on prostatic response to androgen in orchiectomized rats

The effects of hypophysectomy and prolactin replacement therapy on prostatic response to androgen in orchiectomized rats were studied. Castration 23 days prior to treatment with testosterone propionate (TP), followed by hypophysectomy 13 days before TP treatment, and then treatment with 1 mg TP every other day for 16 days caused a greater decrease in body weight, prostatic weight, and the level of citric acid in the prostate than did TP treatment, castration, and sham hypophysectomy. This suggests the existence of a pituitary factor in the maintenance of prostatic integrity. Prolactin replacement therapy in hypophysectomized, castrated,TP-treated rats significantly (p less than .005) increased the prostatic weight and both the content and concentration of citric acid. The results confirm previously reported observations that the prostatic response to androgens is markedly reduced by hypophysectomy in castrated rats, and that prolactin acts synergistically wtih testosterone in promoting prostatic growth and the concentration of citric acid in the prostate. The direct effects of both hypophysectomy and prolactin replacement therapy on the ventral and dorsolateral lobes of the prostate were also demonstrated.     

PNU 157706, a novel dual type I and II 5alpha-reductase inhibitor

PNU 157706 is a novel dual inhibitor of 5alpha-reductase (5alpha-R), the enzyme responsible for the conversion of testosterone (T) to 5alpha-dihydrotestosterone (DHT). Tested on a crude preparation of human or rat prostatic 5alpha-R, PNU 157706 caused enzyme inhibition with IC50 values of 20 and 34 nM, respectively, compared to the values of 32 and 58 nM shown by finasteride. Furthermore, PNU 157706 was highly potent in inhibiting human recombinant 5alpha-R type I and II isozymes, showing IC50 values of 3.9 and 1.8 nM and, therefore, it was several folds more potent than finasteride (IC50 values of 313 and 11.3 nM), particularly on the type I isozyme. PNU 157706 was shown to have no binding affinity for the rat prostate androgen receptor (RBA 0.009% that of DHT). In adult male rats, a single oral dose of 10 mg/kg of PNU 157706 caused a marked and longer lasting reduction of prostatic DHT than did finasteride (at 24 h inhibition by 89 and 47%, respectively). In prepubertal, T- or DHT-implanted castrated rats, PNU 157706, given orally for 7 days at the dose of 10 mg/kg/day, markedly reduced ventral prostate weight in T- but not in DHT-implanted animals, thus showing to be devoid of any anti-androgen activity. In adult rats treated orally for 28 days, PNU 157706 resulted markedly more potent (16-fold) than finasteride in reducing prostate weight, the ED50 values being 0.12 and 1.9 mg/kg/day, respectively. These results indicate that PNU 157706 is a promising, potent inhibitor of both type II and I human 5alpha-R with a very marked antiprostatic effect in the rat.     

Comparison of the effects of stanozolol, oxymetholone, and testosterone cypionate on the sexual behavior of castrated male rats.

In 3 experiments, adult male Long-Evans rats were castrated and treated daily with an anabolic-androgenic steroid (AAS) compound (either stanozolol, oxymetholone, or testosterone cypionate) for 6 weeks. Subjects were assigned to 5 groups that received injections of a high, medium, or low dose of the AAS, testosterone propionate, or the oil vehicle. Stanozolol failed to maintain ejaculation at any dose tested. Although some subjects receiving the low dose of oxymetholone ejaculated, oxymetholone generally failed to stimulate ejaculation above the levels of the oil group. Testosterone cypionate sustained ejaculation at all doses tested. The relative potency of the medium dose of each AAS in the sex accessory tissues was (from most potent to least potent): testosterone cypionate?>?stanozolol?=?oxymetholone?=?oil. Thus, these 3 AAS compounds produced a range of behavioral and endocrine responses in castrated male rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tamoxifen exerts testosterone-dependent and independent effects on thymic involution

Circulating testosterone concentrations and seminal vesicles weights, as well as thymus and spleen weights and histology were assessed in male Wistar rats from the infantile to post-pubertal period. The widely used anti-estrogenic agent tamoxifen was then administered in adult intact and castrated male rats and its long-term effects on thymic involution and splenic growth were examined. The results showed that: (1) age-related involution of the male thymus from the juvenile period through puberty to post-puberty depends on the rising testosterone levels and represents mainly a decrease of thymic lymphoid-cell elements; (2) tamoxifen administration reverses thymic involution in intact adult male rats and this effect is related to a dose-dependent, tamoxifen-induced castration and decrease of testosterone levels; (3) the changes of circulating testosterone levels, either resulting from maturity, or induced by tamoxifen or by castration, have a minimal effect on splenic growth and weight; and (4) in contrast to intact animals, administration of tamoxifen at pharmacological doses to adult castrated rats results in thymic regression. Underscoring the critical role of testosterone on thymic involution, these findings show that tamoxifen is able to reverse ageing changes in the thymus by suppressing testosterone production, while conversely, exerts thymolytic effects in the absence of androgens.     

In vivo characteristics of injectable poly(DL-lactic acid) microspheres for long-acting drug delivery

Poly(DL-lactic acid) (PLA) microspheres containing testosterone (T) were prepared by the solvent evaporation process to evaluate their physical properties such as size distribution, shape, drug content, in vivo controlled drug release, pharmacological influences on the prostate gland in castrated rats, and histopathological findings of tissues surrounding the implants. The in vivo release of T from PLA microspheres containing 30 mg of drug obtained with chloroform was continued over a 6-week period. This effect is attributed to high dispersibility of T in the device when obtained with chloroform. Both serum drug levels and prostate gland weight recovery suggested the effects of a long-acting drug delivery system. The histopathological findings showed that the devices used were completely degraded 10 weeks after injection.     

Expression of G1 cyclins, cyclin-dependent kinases, and cyclin-dependent kinase inhibitors in androgen-induced prostate proliferation in castrated rats

Androgen induces prostate cell proliferation in the castrated rat. We hypothesized that G1 cyclins, cyclin-dependent kinases (cdk), and cdk inhibitors mediate this cellular response to mitogenic signals. In this study, induction of cyclins D1, D2, D3, E, and cdks 2, 4, and 6 expression was observed at various time points during testosterone replacement in the ventral prostate of castrated rats. The induction followed prostate epithelium proliferation, which peaked at 48 h and decreased at 120 h during the treatment. The study of cyclin/cdk complex formation revealed that more cyclin D1/cdk4 and cyclin D1/cdk6 complexes were formed at 48 h than at 120 h of treatment, but cyclin D1/cdk2 complexes remained the same. Furthermore, both hyperphosphorylated and hypophosphorylated forms of Rb were detected at 48 h, but only the hypophosphorylated form was detected at 120 h of treatment. p21Cip1, which was very abundant in the ventral prostate of castrated and intact rats, was not detected when the prostate started proliferation and increased gradually as proliferation decreased during the androgen treatment. Meanwhile, p27Kip1 dramatically increased after androgen treatment, and the induction levels were less at the peak of prostate proliferation and higher when proliferation was low. The results presented here suggest that expression of G1 cyclins and their related kinases and kinase inhibitors are well regulated after androgen replacement in the ventral prostate of castrated rats. The cooperation between these cell cycle regulators leads to a well-controlled prostate regeneration.     

Effects of external cadmium ions on excitation-contraction coupling in rat soleus fibres

Administration of 4 mg of the antisteroid RU486 over 8 consecutive days to adult male rats dissociated in vivo and in vitro gonadotrophin secretion, increasing FSH and decreasing LH secretion. In subsequent experiments we evaluated the involvement of testicular or adrenal secretory products, as well as hypothalamic LHRH, in the effects of 4 consecutive days of RU486 treatment on the secretion of gonadotrophins. The first day of RU486 injection was designated day 1, subsequent days being numbered consecutively. Groups of rats injected with oil (0.2 ml) or RU486 (4 mg) were: (i) injected s.c. from day 1 to day 4 with the antiandrogen flutamide (10 mg/kg); (ii) bilateral orchidectomized (ORCH) on day 1; and (iii) bilateral adrenalectomized (ADX) on day 1. Controls were given flutamide vehicle or were sham operated. To ascertain whether the secretion of LHRH is involved in the effects of RU486 on gonadotrophin secretion, we measured the LHRH secretion into the pituitary stalk blood vessels at 1100 h on day 5 in oil- or RU486-treated rats. Additional oil- and RU486-treated rats were injected i.p. with 100 ng LHRH at 1000 h on day 5, or s.c. with 1 mg LHRH antagonist (LHRH-ANT) at 1000 h on days 2 and 4. Controls were given saline. All animals were decapitated at 1100 h on day 5, trunk blood collected and serum stored frozen until FSH, LH and testosterone assays.%While ADX had no effect on FSH and LH secretion in either oil- or RU486-treated rats, the removal of androgen negative feedback with flutamide treatment or by ORCH substantially increased serum levels of FSH and LH in both oil- and RU486-treated rats, and thus annulled the effects of RU486. No differences in pituitary stalk plasma LHRH concentrations were found between oil- and RU486-treated rats. Injection of LHRH increased serum FSH and LH concentrations in oil-treated rats but only, and to a lesser extent, LH concentrations in RU486-treated rats. Treatment with LHRH-ANT decreased serum concentrations of FSH and LH in both oil- and RU486-treated rats. These results suggest that RU486 inhibited LHRH-stimulated LH secretion at the pituitary level, and that FSH secretion increased in response to a reduction in the negative feedback of androgen.     

Effect of estradiol-17beta & estriol-3-methyl ether on spermatozoa & genital organs of rats

The effect of estradiol-17beta (E2) and estriol-3-methyl ether on spermatozoa and genital organs was investigated in rats. The motility pattern of spermatozoa in epididymis and vas deferens was adversely affected by both treatments in intact rats. The number of spermatozoa in cauda epididymis was significantly (p less than .05) reduced after treatment with estriol-3-methyl ether, however, the combined treatment had a more severe effect. Sperm transport was accelerated after both treatments in castrated rats. No effect was observed on weight and gross histology of testis. Epididymis weight was reduced only after combined treatment. The weight of seminal vesicles, ventral prostate, and vas deferens was reduced after both treatments. However, in castrated rats there was a transient increase in the weight of vas deferens and seminal vesicles after 7 days of E2 treatment while ventral prostate weight was reduced.     

Effect of synthetic progestins on the uptake of labelled testosterone and estradiol-17beta by the accessory genital organs of male rats

The effect of pretreatment with norethindrone (NE) or 17-hydroxyprogesterone caproate (17-OHPC) on the uptake of tritiated testosterone and estradiol-17beta by the accessory sex organs of castrated and intact rats was investigated. A selective in vivo increase in the incorporation of tritiated testosterone and estradiol-17beta was observed at 48 hours after castration. The uptake of testosterone was greatest in the epididymis, while the maximum incorporation of estradiol-17beta was by the vas deferens. Pretreatment with NE or 17-OHPC decreased the incorporation of testosterone by all the accessory organs of castrated rats. NE decreased the incorporation of tritiated estradiol-17beta in the epididymis and seminal vesicles only, while 17-OHPC decreased the uptake in all accessory organs.     

Age-dependent effects of hippocampal muscarinic receptor blockade on memory-based learning in the developing rat

In the male rat, testosterone has been shown to regulate gonadotrophin synthesis and secretion under experimental conditions such as castration or gonadotrophin-releasing hormone (GnRH) antagonist with or without testosterone. The present study aims at clarifying the effects of non-steroidal antiandrogens, Casodex and flutamide, and ethane dimethane sulphonate (EDS) on the regulation of gonadotropin synthesis and secretion. To enable a direct comparison within this study to expected effects of testosterone, a GnRH antagonist-treated group and a castrated group were included. The gene expression of the subunits was correlated with changes in the pituitary and plasma content of immunoreactive luteinizing hormone (LH) and follicle-stimulating hormone (FSH), free subunits and pituitary content of in vitro bioactive LH and FSH. Groups of ten male rats each received the following treatments for 7 days: (1) vehicle; (2) castration; (3) EDS (75 mg/kg); (4) GnRH antagonist (Cetrorelix 250 micrograms/kg/day), (5) Casodex (20 mg/kg/day) or (6) flutamide (20 mg/kg/day). The effectiveness of testosterone deprivation was demonstrated by the reduction of weight in androgen-dependent organs such as epididymides and seminal vesicles in the treated groups. Treatment with flutamide, EDS or castration significantly increased (p < 0.05) serum levels of LH, FSH and alpha-subunit, whereas serum gonadotrophin levels were decreased in the GnRH antagonist-treated group. alpha-Subunit mRNA levels were elevated in the castrated, EDS and flutamide group and LH-beta mRNA levels were increased in the castrated and EDS group. FSH-beta mRNA levels were increased in the castrated group and decreased in the GnRH antagonist group, but remained unchanged in the flutamide and EDS group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Androgen-dependent protein interactions within an intron 1 regulatory region of the 20-kDa protein gene

The 20-kDa protein gene is androgen regulated in rat ventral prostate. Intron 1 contains a 130-base pair complex response element (D2) that binds androgen (AR) and glucocorticoid receptor (GR) but transactivates only with AR in transient cotransfection assays in CV1 cells using the reporter vector D2-tkCAT. To better understand the function of this androgen-responsive unit, nuclear protein interactions with D2 were analyzed by DNase I footprinting in ventral prostate nuclei of intact or castrated rats and in vitro with ventral prostate nuclear protein extracts from intact, castrated, and testosterone-treated castrated rats. Multiple androgen-dependent protected regions and hypersensitive sites were identified in the D2 region with both methods. Mobility shift assays with 32P-labeled oligonucleotides spanning D2 revealed specific interactions with ventral prostate nuclear proteins. Four of the D2-protein complexes decreased in intensity within 24 h of castration. UV cross-linking of the androgen-dependent DNA binding proteins identified protein complexes of approximately 140 and 55 kDa. The results demonstrate androgen-dependent nuclear protein-DNA interactions within the complex androgen response element D2.     

Effect of testosterone propionate treatment on thyrotropin secretion of young and old rats in vitro

The aim of this study was to evaluate the influence of androgens on TSH secretion during aging in Dutch rats. Male young (2 months) and old (16-21 months) rats were castrated (Cx) or sham-operated (C) and received testosterone propionate (TP--4 mg/Kg B.W., i.m., 7 days) or vehicle. Female adult (3 months) and old (12 and 17 months) intact rats received TP or corn oil in the same dose. The rats were decapitated, trunk blood was collected and anterior pituitaries were dissected out for in vitro incubation. In Cx young male rats, only TSH pituitary content showed lower levels than in their controls. Cx TP-treated rats showed higher serum TSH and in vitro basal and TRH-induced TSH secretion, but TP only partially reversed the decrease in pituitary TSH promoted by castration. The old male rats showed lower basal in vitro TSH secretion and pituitary TSH content. In Cx old male rats, serum and basal in vitro TSH concentrations were higher than those of old controls and TP treatment further increased basal in vitro TSH secretion, as well as, stimulated TRH-induced TSH secretion. Interestingly, TP had no effect on intact young or old male rats. However, in intact old female rats, TP stimulated in vitro TSH secretion but, as observed in the intact male, TP had no effect on adult female rats. These results suggest a stimulatory role of testosterone on TSH secretion of young and old male rats. Thereafter, it seems that the testes of old rats secrete some testicular factor that inhibits TSH secretion. However, in male rats with normal testosterone levels TP treatment did not increase further TSH secretion, but in old female rats it had a stimulatory effect.     

Hypothalamus-pituitary-ovarian axis in cyclic rats lacking progesterone actions

Antagonizing diestrous progesterone actions in cyclic rats by s.c. injections of the antiprogesterone RU486 (2 mg twice a day from metestrus through proestrus) increased LH and decreased FSH basal serum concentrations. Ovariectomy at metestrus (0800 h) increased serum levels of both gonadotropins in controls and reversed the RU486-induced dissociation of basal gonadotropin secretion. RU486-dissociated gonadotropin secretion is also dependent upon LHRH, since treatment (s.c.) with 1 mg GnRH antagonist (ORG 30276) twice a day on metestrus and diestrus completely prevented both the RU486-induced increase in LH and the decrease in FSH serum concentrations. The LHRH content in the medial basal hypothalamus and median eminence increased on proestrous morning in RU486-treated rats. The LH pituitary response to an exogenous i.v. bolus of 25 ng LHRH (Peninsula 7201; Peninsula Laboratory, Inc., Merseyside, UK) at 1700 h on diestrus was enhanced in rats treated with RU486. No differences in pituitary FSH response were noted with respect to oil-injected rats. The pituitary content of both gonadotropins decreased in RU486-treated rats on proestrous morning. All these effects due to RU486 in cyclic rats were reversed by ovariectomy. Testosterone serum levels increased significantly from diestrus onward, and the estradiol concentration increased on proestrous morning in RU486-treated rats. Ovariectomy as well as LHRH antagonist treatment eliminated the effects of RU486 on ovarian steroid production. Moreover, antiestrogen tamoxifen treatment reversed RU486-dissociated gonadotropin secretion, while antiandrogen flutamide treatment had no effect. The results of this experiment have confirmed previous findings that RU486 treatment dissociates basal gonadotropin secretion in cyclic rats. In addition, the present results show that: (1) this effect of RU486 is not due to a direct effect of this compound or to the blockade of progesterone action at a central level; (2) the effect of RU486 on pituitary gonadotropin secretion depends on ovarian substances other than progesterone and LHRH, since it is reversed by ovariectomy and completely abolished by LHRH antagonist treatment; (3) the reduction in FSH serum levels in rats treated with RU486 seems to be exerted by inhibin and estradiol at the pituitary level by reducing FSH synthesis and secretion; and (4) the hypersecretion of LH in rats treated with RU486, as compared to that resulting from ovariectomy, seems to be the consequence of, first, a lack of progesterone inhibitory action on LH secretion, and, second, an inappropriate feedback system involving increased hypothalamic LHRH activity and pituitary sensitivity to LHRH of moderately high levels of estradiol in the presence of abnormally high levels of testosterone.