Evaluation of a peripherally selective antiandrogen (Casodex) as a tool for studying the relationship between testosterone and spermatogenesis in the rat

Testicular blood supply is altered in the 41,XXY* Klinefelter syndrome mouse model

Hypergonadotropic hypogonadism is a major feature of Klinefelter syndrome (KS), assumed to be caused by testicular hormone resistance. It was previously shown that intratesticular testosterone levels in vivo and Leydig cell function in vitro seem to be normal indicating other functional constraints. We hypothesized that impaired testicular vascularization/blood flow could be a co-factor to the observed hypergonadotropic hypogonadism. We evaluated the testicular vascular system by measuring blood vessel sizes during postnatal development and testis blood flow in adult 41,XX^Y* mice. Proportional distribution and size of blood vessels were analyzed during testicular development (1, 3, 5, 7, 10, 21 dpp, 15 wpp). While ratios of the vessel/testis area were different at 15 wpp only, a lower number of smaller and mid-sized blood vessels were detected in adult KS mice. For testicular blood flow determination we applied contrast enhanced ultrasound. Floating and reperfusion time for testicular blood flow was increased in 41,XX^Y* mice (floating: XY* 28.8 ± 1.69 s vs XX^Y* 44.6 ± 5.6 s, p = 0.0192; reperfusion XY* 19.7 ± 2.8 s vs XX^Y*: 29.9 ± 6.2 s, p = 0.0134), indicating a diminished blood supply. Our data strengthen the concept that an impaired vascularization either in conjunction or as a result of altered KS testicular architecture contributes to hormone resistance.

Life-long testosterone and antiandrogen treatments affect the survival and reproduction of captive male red-legged partridges (Alectoris rufa)

Abstract

Sexual steroids can play an important role as life-history organizers. In males, high circulating testosterone levels induce physiological/behavioral costs and benefits, leading to trade-offs. However, studies simultaneously testing the impact of these levels in both fitness components (survival and fecundity) during lifetime are scarce and limited to wild birds. To determine the mortality causes or hormonal manipulation impacts on male fertility is, nonetheless, a difficult task in free-ranging animals that could be easier in captivity. We longitudinally monitored captive red-legged partridges (Alectoris rufa) and exposed males to high exogenous testosterone levels, anti-androgens, or a control treatment during each breeding period throughout their lives. Theory predicts that individuals maintaining high androgen levels should obtain higher fitness returns via reproduction, but suffer reduced longevity. Testosterone-treated male partridges, accordingly, lived shorter compared to controls, since they were more prone to die from a natural bacterial infection. However, the same birds seemed to have a lower capacity to fertilize eggs, probably due to endocrine feedback reducing testicular mass. These results show that exogenous testosterone can exert unpredicted effects on fitness parameters. Therefore, caution must be taken when drawing conclusions from non-fully controlled experiments in the wild. Males treated with the androgen-receptor blocker flutamide did not outlive controls as predicted by the life-history trade-off theory, but their mates laid eggs with higher hatching success. The latter could be due to mechanisms improving sperm quality/quantity or influencing maternal investment in egg quality. Testosterone receptor activity/amount could thus be as relevant to fitness as testosterone levels.

Significance statement

It has repeatedly been hypothesized that high testosterone levels induce a cost in terms of reduced lifetime reproductive success. This can be due to reduced fecundity or via shorter lifespan. This is, however, only supported by a handful of studies, mostly in wild birds. We tested this in captive male red-legged partridges, which allowed us to determine reproductive success and mortality causes. We increased testosterone levels or blocked its action with antiandrogens throughout life. High testosterone levels reduced the survival by making birds more prone to die by infection. The eggs produced by their mates also showed lower hatching success, a probable manipulation artifact that should be considered in avian studies in the wild. Interestingly, the androgen-receptor blocker flutamide increased lifetime hatching success compared to controls, suggesting that androgen receptor amounts/activity are even more relevant to fitness than testosterone levels.

Investigations on the dose-response relationship of combined exposure to low doses of three anti-androgens in Wistar rats

The current investigation examines whether combined exposure to three anti-androgens (flutamide, prochloraz, vinclozolin) result in interference with endocrine homeostasis when applied at very low dose levels, and whether the results of combined exposure are more pronounced than to the individual compounds. A pre-post-natal in vivo study design was chosen with more parameters than regulatory testing protocols require (additional endpoints addressing hormone levels, morphology and histopathological examinations). Dose levels were chosen to represent the lowest observed adverse effect level (LOAEL), the no observed adverse effect level (NOAEL), and the acceptable daily intake for each individual substance. Anti-androgenic changes were observable at the effect level (LOAEL) but not at lower exposures. Nipple/areola counts appeared to be a sensitive measure of effect, in addition to male sex organ weights at sexual maturation, and finally gross findings. The results indicate the absence of evidence for effects at low or very low dose levels. No (adverse) effects were seen at the NOAEL dose. A non-monotonic dose-response relationship was not evident. Combined exposure at LOAEL level resulted in enhanced responses for anogenital index, number of areolas/nipples, delayed preputial separation and reduced ventral prostate weight in comparison to the individual compounds.

Aromatase expression in human peripheral blood leucocytes (PBLs) and in various tissues in primates: studies in elderly humans and cynomolgus monkeys

BACKGROUND

Previous analysis of aromatase gene and protein expression in peripheral blood leucocytes (PBLs), studied in children and adults, was extended to elderly subjects. In addition, we assessed whether aromatase expression in PBLs could be used as a parameter of aromatase expression in other tissues, using the cynomolgus monkey as model.

METHODS

Real-time PCR analysis of aromatase gene expression and protein evaluation by Western blot was performed in PBLs of human elderly subjects and in various tissues from cynomolgus monkeys.

RESULTS

No gender-related difference in CYP19A1 mRNA and protein expression in PBLs from human elderly women and men was found. In elderly male cynomolgus monkeys, CYP19A1 mRNA and protein were expressed in all cells and tissues analysed, with the lowest levels in PBLs but no clear-cut correlation with other tissues.

CONCLUSIONS

Aromatase expression in PBLs in elderly human subjects is not gender-related and cannot be a surrogate of aromatase expression for other tissues.

The relative roles of follicle-stimulating hormone and luteinizing hormone in maintaining spermatogonial maturation and spermiation in normal men

CONTEXT

Male hormonal contraception via gonadotropin and intratesticular androgen withdrawal disrupts spermatogenesis at two principal sites: 1) spermatogonial maturation, and 2) spermiation.

OBJECTIVE

The objective of this study was to explore the relative dependence of each stage of germ cell development on FSH and LH/intratesticular androgen action.

DESIGN, SETTING, AND PARTICIPANTS

Eighteen men enrolled in this prospective, randomized 14-wk study at Prince Henry's Institute.

INTERVENTIONS

Subjects (n = 6/group) were assigned to 6 wk of 1) testosterone (T) implant (4 x 200 mg sc once)+depot medroxy progesterone acetate (DMPA; 150 mg im once); 2) T implant+DMPA+FSH (300 IU sc twice weekly); and 3) T implant+DMPA+human chorionic gonadotropin (hCG; 1000 IU sc twice weekly as an LH substitute). Men then underwent a vasectomy and testicular biopsy with previously reported control data used for comparison.

MAIN OUTCOME MEASURES

Germ cell number (assessed by the optical disector stereological approach) and intratesticular androgen levels were determined.

RESULTS

T+DMPA alone significantly suppressed type B spermatogonia, preleptotene through to pachytene spermatocytes, and round spermatids from control (P < 0.05). All germ cell subtypes were maintained at control levels by either FSH or LH activity, except pachytene spermatocytes, which were found to be lower in the hCG vs. FSH (P < 0.01) and control groups (P < 0.05).

CONCLUSIONS

FSH and LH maintained spermatogenesis independently in this gonadotropin-suppressed model. Compared with LH, FSH showed better maintenance of pachytene spermatocyte number, whereas improved conversion to round spermatids was suggested with hCG treatment. Future contraceptive treatment strategies must consider independent regulation of spermatogenesis by both FSH and LH/intratesticular androgens for maximum efficacy.

Estrogenic induction of spermatogenesis in the hypogonadal (hpg) mouse: role of androgens

Testicular development is arrested in the hypogonadal (hpg) mouse due to a congenital deficiency of hypothalamic gonadotropin-releasing hormone synthesis. Previous studies have demonstrated that chronic treatment of these mice with estradiol induces testicular maturation and qualitatively normal spermatogenesis, but it is not known whether these are direct effects via estrogen receptors expressed in the testis, or indirect actions via the pituitary gland. The aim of the current studies was to determine whether the actions of estradiol require the presence of androgens. Sensitive assays revealed that chronic estradiol treatment produced time-dependent increases in pituitary FSH production but no increases in pituitary LH or testicular testosterone content could be detected. As a functional test of androgen dependence, hpg mice were treated for 70 days with estradiol plus Casodex (bicalutamide), an androgen receptor antagonist. Casodex treatment markedly attenuated both the estradiol-induced increase in testicular weight and the proliferation of the seminiferous epithelium, as revealed by morphometric analysis. However, it did not affect the estradiol-induced increase in pituitary FSH content, nor did it affect estradiol-induced increases in the weight of the seminal vesicles and epididymides. We conclude that increased FSH production is not sufficient to explain the increase in testicular development induced by estradiol in hpg mice; there is a requirement for functional androgen receptors for induction of testicular growth.

(+)-(2R,5S)-4-[4-Cyano-3-(trifluoromethyl)phenyl]-2,5-dimethyl-N-[6-(trifluoromethyl)pyridin-3- yl]piperazine-1-carboxamide (YM580) as an Orally Potent and Peripherally Selective Nonsteroidal Androgen Receptor Antagonist

A novel series of trans-N-aryl-2,5-dimethylpiperazine-1-carboxamide derivatives was synthesized and their androgen receptor (AR) antagonist activities and in vivo antiandrogenic effects were evaluated. Pharmacological assays indicated that compound 33 was a potent AR antagonist, and subsequent optical resolution provided (+)-(2R,5S)-4-[4-cyano-3-(trifluoromethyl)phenyl]-2,5-dimethyl-N-[6-(trifluoromethyl)pyridin-3-yl]piperazine-1-carboxamide (33a, YM580) which exhibited the most potent antiandrogenic activity. Unlike bicalutamide, compound 33a decreased the weight of rat ventral prostate in a dose-dependent manner (ED(50) = 2.2 mg/kg/day), and induced the maximum antiandrogenic effect, comparable to that of surgical castration, without significantly affecting serum testosterone levels. Compound 33a is a promising clinical candidate for prostate cancer monotherapy.

Identification of testosterone-regulated genes in testes of hypogonadal mice using oligonucleotide microarray

FSH and testosterone (T) are required for normal spermatogenesis in mammalian males. These hormones regulate the function of Sertoli cells, which in turn support the differentiation of germ cells in the seminiferous tubules. The molecular targets for these hormones in the testis remain elusive. In this study, we have used hypogonadal (hpg) mice as an in vivo model to examine the actions of T on gene expression in murine testis. This expression pattern was analyzed using Affymetrix Murine GeneChip U74v.2 A, B, C (36,899 transcripts) along with Microarray Suite version 5.0, GeneSpring software, and real-time PCR. hpg mice aged 35-45 d were injected sc with 25 mg testosterone proprionate (TP) in 100 ml of sesame oil, and the animals were killed 4, 8, 12, or 24 h after TP treatments. Untreated hpg mice were used as controls. Gene expression from testes of hpg mice treated with TP was compared with that of testes of untreated hpg mice. At all experimental time points earlier than 24 h, there were more mRNAs with reduced than increased abundance in testes of hpg mice after TP treatment. This study suggests that in murine testis, the primary action of T might be to repress gene expression.

Pharmacokinetics and degree of aromatization rather than total dose of different preparations determine the effects of testosterone: a nonhuman primate study in Macaca fascicularis

Currently available testosterone (T) preparations differ substantially in their pharmacokinetic profile that might influence their androgenic properties in terms of suppression of the gonadal axis, effects on anabolic parameters, lipid metabolism, and erythropoiesis. The present work was undertaken to determine the physiological effects of three T preparations with different serum kinetics. Twenty adult male cynomolgus monkeys (Macaca fascicularis) were randomly assigned to receive treatment for 28 weeks with either T enanthate (TE) every 4 weeks, T buciclate (TB) every 7 weeks, or T undecanoate (TU) every 10 weeks or remaining untreated (controls). Each injection delivered 20 mg pure T per kilogram body weight. Pharmacokinetic profiles demonstrated higher peak levels of T for TE-treated animals; serum half-lives were longer for TU or TB. Estradiol levels (area under the curve) were significantly higher in TB vs TU or TE. All T regimens suppressed serum luteinizing hormone bioactivity and testicular volumes declined (all P <.001 vs controls). Sperm counts were markedly lowered in all animals but least in TE (P <.01 vs TB or TU). During recovery phase, return to normal for all three parameters occurred significantly earlier in TE-treated animals, followed by those given TU, compared with TB (all P <.001 between groups). Body weight increased significantly during T exposure. This effect was stronger and more sustained in TB vs TU or TE (both P <.001). Serum creatinine and hemoglobin increased with high significance in all T-treated animals (all P <.001 vs controls). The lowering impact of T on serum lipids was markedly stronger in the longer-acting T preparations in comparison with TE, as were effects on purine metabolism (all P <.001). The pattern of exposure and degree of aromatization rather than overall exposure to T determine its effects in the preclinical primate model. Both fluctuations of androgen concentrations and the conversion rate to estradiol influence gonadal suppression as well as metabolism. These results have to be considered in men receiving treatment for hypogonadism or regimens for hormonal contraception.

Organization of seminiferous epithelium in primates: relationship to spermatogenic efficiency, phylogeny, and mating system

The succession in time and space of specific germ cell associations, denoted as spermatogenic stages, is a typical feature of mammalian spermatogenesis. The arrangement of these stages is either single stage (one spermatogenic stage per tubular cross-section) or multistage (more than one spermatogenic stage per tubular cross-section). It has been proposed that the single-stage versus multistage arrangement is related to spermatogenic efficiency and that the multistage arrangement is typical for hominids. In the present work, the arrangement of spermatogenic stages and the spermatogenic efficiency of 17 primate species, comprising Strepsirrhini (Prosimians: Lemuriformes, Lorisiformes), Platyrrhini (New World primates), Catarrhini (Old World primates), and Hominoidea (great apes and humans), were analyzed comparatively by quantitative histological and flow cytometric means. We found a predominant single-stage tubular organization in the Strepsirrhini, indicating that the single-stage form represents the ancestral state. The highest degree of multistage complexity was found in Hominoidea (except orangutan) and in Platyrrhini, but not in Catarrhini. Hence, no direct relationship between single-stage/multistage tubular topography and phylogeny could be established across primates. In fact, the tubule arrangement seen in Platyrrhini and Catarrhini primates is the reverse of what might be expected from phylogeny. Interestingly, spermatogenic efficiency was similar in all species. We found no correlation between single-stage/multistage arrangement and spermatogenic efficiency or mating system. We speculate that the presence of a single-stage/multistage organization might simply reflect germ cell clonal size. Our findings further indicate that sperm competition in primates is not reflected at the level of testicular function.

Effects of Vinclozolin Administration on Sperm Production and Testosterone Biosynthetic Pathway in Adult Male Rat

The effect of vinclozolin (VCZ), used as a fungicide and known to have anti-androgenic effects on spermatogenesis and gene expression in the male rat testis was investigated. In Experiment 1, VCZ (100 mg/kg/day) or flutamide (FM, 25 mg/kg/day) was orally administered to male Holzman rats for six days. 8 days after the last administration (D8), a drastic increase in intratesticular testosterone was detected in FM (4.2-fold over control) but not in VCZ treated animals, whereas on D36 post-administration, both groups showed similar levels. Significant decreases in daily sperm production were seen in both VCZ and FM-treated rats on D36. Semiquantitative RT-PCR analysis with testicular and pituitary mRNAs on D8 revealed that LHbeta and FSHbeta mRNAs were increased in the pituitary by VCZ, as well as by FM. Among the four testicular steroidogenic enzyme genes, cytochrome P450 side chain cleavage (P450scc) and cytochrome P450 17alpha/C(17-20) lyase (P450c17) mRNAs were significantly increased, whereas 17beta-hydroxysteroid dehydrogenase type III (17betaHSD) mRNA was not changed. A significant increase in 3beta-hydroxysteroid dehydrogenase type I (3betaHSD) and a decrease in androgen receptor (AR) mRNA were observed only in FM treated rats. Immunohistochemistry demonstrated intense staining of P450scc in the interstitial cells of VCZ-treated testis on D8. In Experiment 2, hormone levels were measured at 1, 3, 6, 12 and 24 hours after VCZ (100 mg/kg) administration to Sprague-Dawley rats. Serum LH level remained constant for the first 3 hours and started to increase at 6 hrs. In contrast, serum and intratesticular testosterone levels increased 2-fold at 1 hr and maintained the level until 24 hrs. P450c17 mRNA level was 2-fold increased at all periods, whereas no obvious changes were detected in the other steroidogenic enzyme genes. Although not statistically significant, AR mRNA level increased 2-fold, 3 hrs after VCZ administration. These results indicate that VCZ affects the pituitary in a similar manner as FM, but functions differently on testicular gene expression.

Alterations of Gene Expression in Adult Male Rat Testis and Pituitary Shortly After Subacute Administration of the Antiandrogen Flutamide

In the course of profiling alterations of gene expression in the male reproductive system induced by anti-androgenic agents, 28 genes expressed in the testis or pituitary of adult rats were examined shortly after subacute administration of the well-known anti-androgen, flutamide (FM). FM (25 mg/kg/day) was orally administered to male rats for six days. On day 8 (D8) after the first dose of FM, intratesticular testosterone (T) levels had dramatically increased, but daily sperm production on D36 was significantly decreased. The mRNA levels of testicular and pituitary genes on D8 were measured by semiquantitative RT-PCR. Among the six testicular steroidogenic enzyme genes, the mRNAs of the P450 side chain cleavage, P450 17 alpha/C(17-20) lyase, and 3beta-hydroxysteroid dehydrogenase type I (3betaHSD) genes significantly increased, whereas 17beta-hydroxysteroid dehydrogenase type III slightly decreased. Among the three steroid receptors examined, androgen receptor (AR) and glucocorticoid receptor (GR) mRNAs were significantly down-regulated (29% and 35%, respectively) in the testis, but there was no change in estrogen receptor alpha. There were no clear changes in expression of the gonadotropin receptors and Sertoli cell specific genes, but a slight increase was observed in expression of the lactose dehydrogenase-c mRNA, a germ cell specific gene. Among the three immediate early genes, c-myc mRNA was increased approximately 1.4-fold. In the pituitary, on the other hand, mRNAs for LHbeta and FSHbeta subunits and gonadotropin releasing hormone receptor had increased significantly. These results show that subacute FM administration first affected hypothalamus/pituitary hormone gene expression, then altered gonadotropin secretion, and subsequently induced over-expression of testicular steroidogenic enzyme genes. However, the significant up-regulation of 3betaHSD and down-regulation of AR mRNAs, despite the higher level of intratesticular T, might be explained by an antagonistic action of hydroxyflutamide retained in the testis. The profiles of alterations in gene expression observed will provide important information for the screening of adult male animals for anti-androgenic chemicals.

Effects of androgens and antiandrogens on the quantitative immunohistochemistry of gonadotrope cells in prepubertal male rats

In the male rat, androgens are involved in the feedback regulation of gonadotropin synthesis and secretion. Specific androgen-receptor blockade by the nonsteroidal antiandrogens, flutamide and Casodex, has proven to be a valid tool for studying androgen effects in vivo. The aim of the present study was to investigate the effect of antiandrogen administration at the pituitary level by evaluating the changes in gonadotropes through quantitative immunohistochemistry, and by comparing these alterations with the effect of androgen deprivation by castration either with or without subsequent androgen replacement. Male Sprague-Dawley rats (23 days old) were randomly divided into 5 groups for the following treatments: (a) controls; (b) flutamide-injected (10 mg/rat/day in a gelatin vehicle); (c) Casodex-injected (10 mg/rat/day in an oil vehicle); (d) castrated, and (e) castrated and dihydrotestosterone propionate-replaced (40 microg/rat/day in an oil vehicle). Groups were then sacrificed after 10 days of maintenance under each condition. Pituitaries were fixed in Bouin's fluid and embedded in paraffin. Serial sections (4 micrometer) were obtained at different levels and immunostained by means of the primary murine monoclonal antibodies anti-FSH and anti-LH and a peroxidase-mediated EnVision System (Dako). Measurements of volume density (VD) and individual mean cell area were made by means of an image-analysis system (Imaging Technology, Optimas). Serum FSH and LH levels were determined by radioimmunoassay (RIA). Serum gonadotropin levels, VD, and mean cell area increased significantly in the flutamide-treated, Casodex-treated, and castrated groups (p < 0.05). Androgen replacement in the castrated rats, however, reduced VD, mean cell area, and serum gonadotropins to levels comparable to those of controls. We conclude that either androgen blockade by antiandrogens or castration produce an enhancement in the gonadotrope cell population in prepubertal rats, as shown by an increase in both VD and mean cell area, as well as an elevation in FSH- and LH-immunoreactive cells. These observations correlate well with the changes found in the levels of circulating gonadotropins as measured by RIA.

Bicalutamide dosages used in the treatment of prostate cancer

BACKGROUND

Androgen deprivation is often used for the treatment of patients with prostate cancer. Androgen deprivation can be achieved by surgical castration or medical castration, with or without using an antiandrogen. Each of these treatments may be used alone, or an antiandrogen may be used alongside castration to produce combined androgen blockade therapy.

METHODS

The nonsteroidal antiandrogen, bicalutamide (Casodex), has been evaluated as a component in combined androgen blockade and as monotherapy. We review the arguments that indicate why a 50-mg once-daily dose of bicalutamide is appropriate in combined androgen blockade, while ongoing clinical trials evaluate 150-mg once-daily as monotherapy in the treatment of prostate cancer.

RESULTS

The choice of the 50-mg dose of bicalutamide when used in combined androgen blockade is supported by four main arguments. First, bicalutamide 50 mg is at least equivalent to, if not better than, flutamide 750 mg in terms of receptor affinity, potency, and favorable plasma concentration profile. Second, the reduction in testosterone concentrations produced by medical or surgical castration decreases the potential competition between bicalutamide and testosterone for androgen receptors in prostate cells, allowing the use of a lower dose of antiandrogen in combined androgen blockade than is necessary in monotherapy. Third, bicalutamide 50 mg has an excellent tolerability profile. Fourth, at the 50-mg dose, bicalutamide plus luteinizing hormone-releasing hormone analogue was equivalent to flutamide plus luteinizing hormone-releasing hormone analogue, although there was a trend towards longer survival with bicalutamide. Furthermore, investigations of higher doses of bicalutamide have justified evaluation of bicalutamide 150 mg as monotherapy. First, pharmacodynamic studies reveal an increasing prostate-specific antigen response with increasing dose, which appears to plateau at a dose of around 150-200 mg. Second, in an analysis with 31% mortality, bicalutamide 150 mg appeared to have equivalent efficacy compared with castration in terms of survival in patients with nonmetastatic prostate cancer.

CONCLUSIONS

On the basis of available data, bicalutamide 50 mg is an appropriate dose to use in combined androgen blockade, while 150 mg is being evaluated in ongoing clinical trials as a suitable dose for monotherapy.

The preclinical development of bicalutamide: pharmacodynamics and mechanism of action

OBJECTIVES. To describe the preclinical development of bicalutamide and clarify its pharmacodynamics and mechanisms of action. Bicalutamide was developed from a series of nonsteroidal compounds related to flutamide that showed a range of pharmacologic activity from full androgen agonist to pure antiandrogen, including progestational and antiprogestational properties. METHODS AND RESULTS. Bicalutamide is a pure antiandrogen that binds to rat, dog, and human prostate; the affinity compared with the natural ligand 5 alpha-dihydrotestosterone is low, but bicalutamide has an affinity for the rat androgen receptor approximately four times higher than hydroxyflutamide, the active metabolite of flutamide. Bicalutamide also binds to androgen receptors found in the LNCaP human prostate tumor and the Shionogi S115 mouse mammary tumor cell line, as well as androgen receptors transfected into CV-1 and HeLa cells. In all cases, bicalutamide behaves as a pure antiandrogen and inhibits gene expression and cell growth stimulated by androgen. Studies with the LNCaP cell line are particularly interesting, as these cells contain a mutated androgen receptor (codon 868, Thr-->Ala), which behaves idiosyncratically with other antiandrogens (cyproterone acetate and flutamide): both these antiandrogens act as agonists in this cell line and stimulate proliferation. Studies in vivo show that bicalutamide is a potent antiandrogen in the rat. In immature, castrated male rats treated daily with testosterone propionate, bicalutamide produces a profound inhibition of accessory sex organ (ventral prostate and seminal vesicles) growth at oral doses as low as 0.25 mg/kg; it is more active in this test than flutamide or cyproterone acetate. In mature male rats, daily oral doses of bicalutamide produce a dose-related reduction in weights of the ventral prostate glands and seminal vesicles: in this test, bicalutamide is around five times as potent as flutamide. In contrast to flutamide, which produces dose-related, marked increases in serum luteinizing hormone (LH) and testosterone as a consequence of the central inhibition of the negative feedback effects of androgens on the hypothalamic-pituitary-tests axis, bicalutamide has little effect on serum LH and testosterone; i.e., it is peripherally selective. The peripheral selectivity of bicalutamide in the rat is not due to differences between the prostate versus hypothalamic or pituitary receptors, as bicalutamide reverses the suppressive effect of testosterone on luteinizing hormone-releasing hormone (LHRH) secretion from hypothalamic slices in vitro and is as effective as flutamide at sensitizing the pituitary gland to secrete LH in response to administered LHRH. The peripheral selectivity of bicalutamide has now been shown to be due to poor penetration across the blood-brain barrier: tissue distribution studies with [3H]bicalutamide show that although it is concentrated in the organs of metabolism and secretion as well as in the prostate, the pituitary glands, and the seminal vesicles, levels in the hypothalamus and the central nervous system (CNS) are much lower than in blood. Indeed, it is probable that levels found in the CNS reflect levels of blood contamination. In dogs, bicalutamide has exquisite potency and causes dose-related atrophy of the prostate gland and epididymides; with an oral ED50 of 0.1 mg/kg, it is around 50 times as potent as flutamide in this species and also more potent than the steroidal antiandrogen WIN49596 and the 5 alpha-reductase inhibitor MK-906. Even at substantial multiples of the active dose (up to 100 mg/kg orally), bicalutamide failed to increase serum testosterone, so it is also peripherally selective in the dog.

Flutamide as a tool to study the hormonal regulation of the reproductive tract in the golden hamster

The effect of flutamide (FLU) administered during 6 weeks at doses of 50 or 100 mg kg-1 body weight, on various reproductive characteristics of sexually active male golden hamsters was studied. The weight of seminal vesicles and epididymides showed a dose dependent inhibition with FLU, while testicular weight exhibited a biphasic response, its value being increased by 20% at lower FLU doses and reduced by 15% at higher FLU doses. An elevation of testicular and epididymal androgen-binding protein (ABP) content and also of testicular testosterone content was observed with both doses of FLU. Serum levels of LH and testosterone exhibited a four-fold increase, at both doses of FLU, while FSH serum level was elevated depending on the dose of FLU used. Results suggest that in the golden hamster the maintenance of the weight of testes and accessory organs depends mainly on androgenic stimulation, while production and transport of ABP is probably regulated by gonadotropins.

Antiproliferative activity of casodex (ICI 176.334) in hormone-dependent tumours

The nonsteroidal antiandrogen casodex has been described as a peripherally selective drug for the treatment of prostatic cancer. In this study we determined its activity in various models of hormone-dependent malignancies including those of the prostate and the breast. Analysis of endocrine effects in rats after 15 days of treatment revealed a strong reduction of the weights of prostates and seminal vesicles and a significant rise of testosterone serum levels as a result of the interference with central feedback mechanisms. The growth of androgen-sensitive human LNCaP/FGC prostate cancer cells was strongly inhibited by casodex. Unlike hydroxyflutamide, casodex was also active in hormone-depleted medium. The inhibitory effect was overcome by addition of testosterone propionate, which indicates an androgen-receptor-mediated mode of action. In rats bearing Dunning R3327-G prostate carcinomas casodex exerted a strong antitumour effect at the beginning of therapy. However, after 4 weeks of treatment tumours resumed growth whereas diethylstilboestrol-treated tumours remained static. In MXT-M3.2 mouse mammary tumours with significant quantities of androgen receptors casodex was also effective in inhibiting tumour growth. After 6 weeks of treatment, tumour weights were reduced by 69% whereas uterine weights were significantly increased, possibly because of a progestin-like activity of the drug. Csodex is very active in various models of hormone-dependent carcinomas. However, the limited duration of action in prostatic tumours and the incomplete growth inhibition in mammary tumours suggest that it should be used only combination with other endocrine therapies.

Regulation of the macrophage population in postnatal rat testis

Testicular macrophages increase in concentration during postnatal development in rats. This process may be under hormonal control since administration of hCG stimulates a similar increase to occur precociously. The purpose of the present studies was to determine how the macrophage population is regulated during normal postnatal development and in response to exogenous hCG. We first determined that testicular macrophages proliferate in situ during development and that hCG administration results in an increase in proliferation when given to 10-day-old rats. We next evaluated whether hCG might exert its effects through enhanced secretion of testosterone from Leydig cells. We found that testosterone could not induce a precocious increment in the macrophage concentration when it was administered to newborn pups for 10 days. Finally, the normal increase in macrophage concentration that occurs prior to puberty could not be blocked by treatment with the antiandrogen Casodex. The results are consistent with the hypothesis that the macrophage population expands by proliferation, perhaps under gonadotropin control. In addition, neither the precocial expansion that occurs in response to hCG nor the normal expansion that occurs before puberty is mediated by testosterone.

Effects of antiandrogens and ethane dimethane sulphonate (EDS) on gene expression, free subunits, bioactivity and secretion of pituitary gonadotrophins in male rats

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)