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Biomedical subjects

G F Weinbauer

Publications and source records attributed to G F Weinbauer.

At least 73 records · Page 4Linked to original sources
PubMed1993

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)

Androgen Antagonists↗
PubMed1993

Restoration of spermatogenesis by follicle-stimulating hormone despite low intratesticular testosterone in photoinhibited hypogonadotropic Djungarian hamsters (Phodopus sungorus).

By exposing male Djungarian hamsters to short-day photoperiods, a hypogonadotropic condition resembling that of hypophysectomized animals can be achieved without resorting to surgery. By use of this animal model, differential effects of gonadotropins on spermatogenesis have been studied revealing that FSH selectively restimulates spermatogenesis up to the level of spermatids. In the present study, we investigated whether FSH (6 IU/day) also restores fertility in hamsters exposed to short-day photoperiods (8L:16D). Animals kept under long-day photoperiod (16L:8D) served as controls. After 8 wk under 8L:16D, gonads were involuted and the animals (n = 9-10 per group) were treated with FSH, or testosterone implants, or both for the following 33 days. An additional group received FSH for 33 days and, for the last 12 days only, FSH plus testosterone to induce copulatory and ejaculatory behavior. The implants caused no increase in intratesticular testosterone as compared to that in short-day controls. All males were paired with adult females for the last 5 days of treatment, and killed thereafter. Litter sizes were determined 22 days later. The examination of the testes by flow-cytometrical techniques revealed qualitatively normal spermatogenesis in animals receiving FSH, whereas testosterone caused an insignificant increase to a few round spermatids. In most FSH-treated animals, sperm were present in the epididymides. In hamsters receiving FSH along with testosterone, treatment resulted in restoration of full fertility as compared to long-day controls. Fertility was also restored in animals receiving testosterone only for the last 12 days of FSH treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

FSH and testosterone, alone or in combination, initiate testicular growth and increase the number of spermatogonia and Sertoli cells in a juvenile non-human primate (Macaca mulatta).

The present study was designed to investigate the relative contributions of FSH and testosterone in the initiation of testicular growth and function in primates. Four groups (n = 4/group) of juvenile rhesus monkeys (Macaca mulatta), 12-18 months old, were treated with vehicle, a highly purified human FSH preparation (hFSH; Fertinorm, 3 IU/kg per day), testosterone (testosterone enanthate, 125 mg/week) or FSH plus testosterone, for a period of 12 weeks. Compared with vehicle treatment, the administration of hormones significantly (P < 0.05) increased testicular weight and volume, and the diameter of seminiferous tubules. The number of Sertoli cells per tubule cross-section also increased significantly (P < 0.05). Numbers of Ad (dark) spermatogonia (reserve stem cells) were not significantly influenced by any treatment. In contrast, the numbers of Ap (pale) spermatogonia (renewing stem cells) were significantly (P < 0.05) stimulated with hFSH and testosterone alone. Following the combined treatment, numbers of Ap spermatogonia were also higher compared with control but this effect did not attain statistical significance. In half of the animals in both testosterone-treated groups, a few prophase I spermatocytes were present. Inhibin concentrations reached adult levels in hFSH-treated groups but remained unaffected by testosterone. Conversely, testosterone failed to influence inhibin levels and, unlike hFSH, increased testicular androgen concentration and epididymal weights. Our observations suggest that hFSH and testosterone alone are capable of initiating testicular growth and gametogenesis in an immature primate. Both hormones probably act via activation of the proliferation of Ap spermatogonia, which are considered to be renewing stem cells within the testis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of FSH and testosterone on intratesticular insulin-like growth factor-I and specific germ cell populations in rats treated with gonadotrophin-releasing hormone antagonist.

Evidence derived predominantly from a series of in-vitro studies indicates that insulin-like growth factor-I (IGF-I) plays an important role as a paracrine and autocrine regulator within the testis. We investigated the effects of FSH substitution on spermatogenesis and testicular IGF-I content in rats treated with gonadotrophin-releasing hormone (GnRH) antagonist (ANT) and injected with ethane dimethane sulphonate (EDS), a Leydig cell toxin. FSH treatment partially prevented the marked decrease in intratesticular IGF-I in rats treated with only GnRH antagonist but not in GnRH antagonist+EDS-treated animals (controls, 191.0 +/- 4.5; ANT, 80.1 +/- 5.6; ANT+EDS, 81.6 +/- 3.4; ANT+EDS+FSH, 86.3 +/- 1.4; ANT+FSH, 137.7 + 7.3 (S.E.M.) ng/testis). Correlation analysis of testicular IGF-I content with the number of pachytene spermatocytes and round spermatids per cross-section revealed r values of 0.77 and 0.74 respectively (P < 0.001). We then analysed the same parameters in GnRH antagonist-treated rats which, in addition, received daily injections of the anti-androgen flutamide, in order to investigate the potential role of testosterone, as opposed to other Leydig cell products, in the regulation of spermatogenesis and testicular IGF-I. FSH treatment prevented regression of spermatogenesis in rats treated with GnRH antagonist alone but not in GnRH antagonist- and flutamide-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The gonadotropin-releasing hormone (GnRH) agonist-induced initial rise of bioactive LH and testosterone can be blunted in a dose-dependent manner by GnRH antagonist in the non-human primate.

Gonadotropin-releasing hormone (GnRH) agonists induce a clinically undesirable, transitory but very pronounced initial rise of gonadotropin and gonadal steroid secretion. We investigated, in a non-human primate model, whether the initial stimulatory effects of GnRH agonists can be avoided by a short period of pretreatment and simultaneous treatment with a GnRH antagonist. Three groups of five adult male cynomolgus monkeys (Macaca fascicularis) received a single s.c. biodegradable implant loaded with the GnRH agonist, buserelin ([D-Ser(TBu)6-desGly-NH2]-GnRH), releasing approximately 50 micrograms buserelin daily. From 1 week before to 1 week after inception of administration of GnRH agonist, group 1 received the GnRH antagonist vehicle, and groups 2 and 3 were given s.c. injections of the GnRH antagonist Nal-Glu ([Ac-D-Nal(2)1,D-4-Cl-Phe2,D-Pal3,D-Arg5,D-Glu6(AA),D- Ala10]-GnRH) at a dose of 450 or 2250 micrograms/kg daily. In the absence of GnRH antagonist, the GnRH agonist induced a marked elevation of serum luteinizing hormone (LH) and testosterone lasting for 2 and 5 days, respectively. In group 2, Nal-Glu reduced basal hormone secretion and delayed the peak of GnRH-agonist-induced hormone secretion by 1 day. In group 3, the GnRH-agonist-induced rise of LH and testosterone was prevented in three animals and did not exceed baseline hormone levels in the other two animals. Areas under the LH and testosterone curves were significantly reduced in group 3 compared to group 1. After withdrawal of the GnRH antagonist, a second transient rise of hormone secretion was observed. Except for testosterone in group 2, this rise did not exceed the baseline range of hormone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effect of testosterone deprivation on expression of the androgen receptor in rat prostate, epididymis and testis.

Adult rats were treated with ethane dimethane sulphonate (EDS) to eliminate the Leydig cells. This treatment resulted in very low levels of testosterone in the blood and in the testis. Furthermore, histological evaluation of spermatogenesis showed no marked differences between control and EDS-treated animals. In the ventral prostate, 5 days after EDS-treatment, a 4.0 +/- 0.3-fold up-regulation of androgen receptor (AR) mRNA was observed, together with a 2.2 +/- 0.2-fold increase in actin mRNA. In the epididymis, a 2.0 +/- 0.5-fold increase in AR mRNA level was observed, without a change in actin mRNA level. In the testes of EDS-treated rats, the AR mRNA level was not changed (1.02 +/- 0.17-fold of controls), and there was also no change in actin mRNA level at 5 days after EDS-treatment. These results indicate that AR mRNA expression in the ventral prostate and epididymis is regulated differentially by testosterone when compared to regulation in the testis. Testicular androgen binding sites were assayed by Scatchard analysis of the binding of 3H-R1881 to a nuclear fraction, that was isolated by a method which involved the use of liquid nitrogen and high sucrose buffer. The number of specific binding sites per testis in EDS-treated rats with testosterone-implants, remained unaltered compared to control rats (9.1 +/- 1.4 pmol/testis). In these rats, 20% of the normal testicular testosterone level was sufficient to maintain the androgen receptor in a tight nuclear binding (transformed) form. In testes from EDS-treated rats without testosterone-implants, the AR did not fractionate into the nuclear fraction; however, the total testicular AR content in these animals was close to control levels, as measured by nuclear 3H-R1881 binding after receptor transformation through injection of a high dose of testosterone (10 mg) 2 h before killing the rats (testosterone pulse). In the different experimental groups, FSH was not required to maintain the total testicular AR content (ligand binding). Immunoprecipitation and Western blotting of the testicular AR using specific monoclonal and polyclonal antibodies indicated that the total testicular amount of immunodetectable AR protein in long-term testosterone deprived rats was very low when compared to that in control rats or rats with testosterone-implants. This is in disagreement with results obtained in the ligand binding assay, and may point to a structural modification of the AR in the testis that possibly occurs in the prolonged absence of androgens.

Animals↗
PubMed1992

Microheterogeneity of pituitary follicle-stimulating hormone in male rats: differential effects of the chronic androgen deprivation induced by castration or androgen blockade.

Testicular androgens are known to influence not only the secretion but also the bioactivity and molecular composition of pituitary FSH. In the present study, we investigated the effects of chronic androgen blockade and castration on the molecular heterogeneity of the gonadotrophin. Groups of male adult rats (five animals per group) received one of the following treatments: vehicle, the non-steroidal anti-androgens casodex (20 mg/kg per day) or flutamide (20 mg/kg per day), or castration. After 8 weeks, the animals were killed and individual pituitary homogenates fractionated by isoelectric focusing (IEF) on sucrose density gradients in the pH range 2.5-8. FSH was measured by radioimmunoassay (RIA) in the individual fractions and by invitro bioassay (Sertoli cell aromatase bioassay) in pools of fractions which were combined according to pH intervals of 0.5 units. Bioactive and immunoreactive FSH were also measured in sera and unfractionated pituitary extracts. Testosterone and inhibin were assayed in sera by RIA. A significant increase in serum immunoreactive and bioactive FSH was demonstrated in flutamide-treated and castrated animals, whereas the pituitary content of bioactive FSH remained unchanged in the four groups. Serum testosterone and inhibin were undetectable in castrated animals and significantly increased in those treated with flutamide. By RIA, the IEF profiles of the flutamide-treated and castrated rats showed a significant reduction of the FSH isoforms with 3.5 < pI < 4, with a significant increase in the isoforms with pI > 4 only in the castrated group.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgen Antagonists↗
PubMed1992

Exogenous gonadotrophin-releasing hormone (GnRH) stimulates LH secretion in male monkeys (Macaca fascicularis) treated chronically with high doses of a GnRH antagonist.

We reported previously that after a single injection of a gonadotrophin-releasing hormone (GnRH) antagonist to male monkeys, exogenous GnRH stimulated LH secretion in a time- and dose-dependent manner, indicating that GnRH antagonist-induced blockade of LH secretion resulted from pituitary GnRH receptor occupancy. The present study was performed to investigate whether GnRH can also restore a blockade of LH and testosterone secretion during chronic GnRH antagonist administration. Four adult male cynomolgus monkeys (Macaca fascicularis) received daily s.c. injections of the GnRH antagonist [N-Ac-D-pCl-Phe1,2,D-TRP3,D-Arg6-D-Ala10]-GnRH (ORG 30276) at a dose of 1400-1600 micrograms/kg for 8 weeks. Before the GnRH antagonist was given and during weeks 3 and 8 of treatment, pituitary stimulation tests were performed with 0.5, 5, 50 and 500 micrograms synthetic GnRH, administered in increasing order at intervals of 24 h. At 8 weeks, a dose of 1000 micrograms GnRH was also given. All doses of GnRH significantly (P less than 0.05) stimulated serum concentrations of bioactive LH (3- to 8-fold) and testosterone (2.6- to 3.8-fold) before the initiation of GnRH antagonist treatment. After 3 weeks of GnRH antagonist treatment, only 50 and 500 micrograms GnRH doses were able to increase LH and testosterone secretion. Release of LH was significantly (P less than 0.05) more elevated with 500 micrograms compared with 50 micrograms GnRH. After 8 weeks, only the highest dose of 1000 micrograms elicited a significant (P less than 0.05) rise in LH secretion. Basal hormone levels just before the bolus injection of GnRH were similar (P greater than 0.10-0.80).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Inhibin-like and gonadotropin-like immunoreactivity in pituitary cells of male monkeys (Macaca fascicularis, Macaca mulatta).

Inhibin-like immunoreactivity was detected by immunocytochemistry in the pituitaries of untreated male crab-eating macaques (cynomolgus monkey) and rhesus monkeys, in rhesus monkeys actively immunized against FSH, and in one orchidectomized crab-eating macaque. Localizations were performed by the immunogold-silver staining with 5-nm colloidal gold-conjugated second or third antibodies and by the alkaline phosphatase-anti-alkaline-phosphatase technique. Two different inhibin-specific antisera, raised against the alpha-subunit or the entire inhibin molecule, provided identical staining patterns. Positive label was confined to the pars distalis of the pituitary and occurred exclusively in the cytoplasm of morphologically different cell types throughout the pars distalis in all pituitaries. Staining was most prominent in clusters of chromophobic cells. The presence of inhibin-like activity in the pituitary of an orchidectomized monkey with undetectable serum inhibin levels suggests that inhibin is produced within the pituitary gland. Co-localization studies for the beta-subunits of the gonadotropic hormones revealed that on average 82% of the gonadotropes were bihormonal. Using the same protocol, co-localization of inhibin-like activity with gonadotropin-like immunoreactivity revealed only a small degree of common distribution (less than 15%). Inhibin-positive cells were frequently in close proximity to gonadotropic cells and, thus, paracrine effects of inhibin on gonadotropin-synthesizing cells are conceivable.

Animals↗
PubMed1991

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

The endocrine profile and the effects on spermatogenesis of the new antiandrogen, Casodex [2RS)-4-cyano-3-(4-fluorophenylsulphonyl)-2-anilide, CAS) were evaluated in the adult rat. In the first experiment rats were administered CAS at daily doses of 10, 20 and 40 mg/kg for 14 days. For comparison groups receiving flutamide (FL, 10 mg/kg) and ethane dimethane sulphonate (EDS) were included. Unlike FL, administration of CAS (10 and 20 mg/kg) did not significantly raise serum concentrations of gonadotropic hormones and testosterone. With 40 mg/kg CAS gonadotropin secretion, but not testosterone levels, were elevated on day 15. Administration of CAS lowered the weight of the seminal vesicles and coagulating glands comparable to the administration of the Leydig cell toxin EDS. In contrast to FL a significant loss of germ cells in stage VII of spermatogenesis was observed with CAS. In a second experiment the ability of FL and CAS to block testicular androgen action was compared in rats with reduced testicular androgen production induced by a gonadotropin-releasing hormone antagonist. Both antiandrogens markedly enhanced spermatogenic involution as revealed by quantitative flow cytometric analysis of germ cell numbers. The study demonstrates that (a) CAS is a peripherally selective antiandrogen and (b) CAS might provide a feasible approach to study androgen dependence of spermatogenesis in the presence of normal FSH levels.

Androgen Antagonists↗
PubMed1991

Regulation of androgen receptor mRNA and protein in the rat testis by testosterone.

Adult rats were treated with ethane dimethane sulphonate (EDS), an agent that destroys Leydig cells. Within 5 days after EDS treatment, the levels of testosterone (T) in the circulation and in the testis were decreased to very low values, which makes it possible to manipulate the testicular T concentration through administration of exogenous T. Spermatogenesis was not markedly affected within 5 days after EDS treatment, also not in the absence of T administration. In testes of EDS-treated rats, the androgen receptor mRNA (ARmRNA) level remained unaltered for 5 days. In ventral prostate, however, this treatment caused a pronounced upregulation of the level of ARmRNA, which could be counteracted by implantation of silastic T implants immediately after EDS treatment. In EDS-treated rats carrying a T implant and in untreated rats, the same number of specific [3H]R1881 binding sites was observed using a total testis nuclear fraction (Scatchard analysis). In testes from EDS-treated rats without T implants, androgen receptors (AR) did not fractionate into the nuclear fraction; however, the total testicular AR content in these animals (measured by nuclear [3H]R1881 binding after receptor transformation through injection of a high dose of T, 2 h before killing the rats) remained unaltered. Immunoprecipitation and Western blotting using anti N-terminal antibodies seemed to indicate that the total testicular amount of AR protein in the EDS-treated rats was very low as compared to that in EDS-treated rats carrying T implants and in untreated rats. Even after receptor retransformation (by injection of a high dose of T) the receptors were not quantitatively detected by immunoprecipitation and Western blotting. This may point to a structural modification of the AR that occurs in the prolonged absence of androgens.

Androgens↗
PubMed1991

Human follicle-stimulating hormone exerts a stimulatory effect on spermatogenesis, testicular size, and serum inhibin levels in the gonadotropin-releasing hormone antagonist-treated nonhuman primate (Macaca fascicularis).

The role of FSH in spermatogenesis was investigated in nonhuman primates depleted of testosterone by GnRH antagonist treatment. The GnRH antagonist antide (Nal-Lys; [N-acetyl-D-2-naphthyl-Ala1,D-4-chloro-Phe2,D-pyridyl-Ala3, nicotinyl-Lys5,D-nicotinyl-Lys6,isopropyl-Lys8,D-Ala10 ]-GnRH) was used at a daily dose of 450 micrograms/kg to suppress endogeneous gonadotropin and androgen production. Four groups of five cynomolgus monkeys (Macaca fascicularis) were subjected to the following treatment throughout a 16-week period: vehicle (group 1), GnRH antagonist (group 2), and GnRH antagonist plus human FSH (Fertinorm; 2 x 15 IU/day.animal; hFSH) during weeks 0-8 (group 3) or 8-16 (group 4). Testicular biopsies were performed before and after 4, 8, and 16 weeks of treatment. The tissue was analyzed by light microscopy and flow cytometry. Serum testosterone levels were suppressed into the range of orchidectomized animals in all GnRH antagonist-treated groups. In the absence of hFSH, serum inhibin levels were also markedly lowered. Concomitant administration of hFSH attenuated the GnRH antagonist-induced reduction of testicular size, while delayed treatment with hFSH failed to restimulate testicular volume. Numbers of A-dark spermatogonia, the reserve stem cells, were not altered by any of the treatments. hFSH either fully maintained or increased the counts for A-pale spermatogonia (renewing stem cells). The development of pachytene spermatocytes and round and elongated spermatids was markedly reduced or inhibited by the GnRH antagonist within 6-18 weeks. In contrasts, hFSH maintained these cell types at about 50% of baseline for 8 weeks. After 8 weeks of GnRH antagonist administration, hFSH stimulated A-pale spermatogonia and spermatocytes 2- to 3-fold with only minor effects on spermatid numbers. By means of flow cytometry, testicular cells were quantified according to DNA content. Within 8-16 weeks of GnRH antagonist treatment the percentage of 4C (mainly primary spermatocytes), 1C (round spermatids), and 1CC cells (elongated spermatids) had fallen from 65-75% to 5-25%. hFSH completely maintained the relative number of these cells, but failed to significantly restimulate the formation of 1CC cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Comparative effects of chronic administration of the non-steroidal antiandrogens flutamide and Casodex on the reproductive system of the adult male rat.

The effects of chronic blockade of androgen action by the antiandrogens flutamide and Casodex on serum and pituitary concentrations of LH and FSH, serum and testicular androgen levels, reproductive organ weights, and on spermatogenesis were compared in the adult rat. Animals were treated for 3 and 8 weeks with vehicle, Casodex (20 mg.kg-1.(day)-1, flutamide (20 mg.kg-1.(day)-1) and GnRH antagonist (150 micrograms/day, Detirelix). Treatment with GnRH antagonist suppressed gonadotropin and testosterone production, reduced the weights of testes, epididymides and seminal vesicles, and inhibited germ cell development. Flutamide administration markedly elevated serum and pituitary levels of gonadotropins as well as serum and testicular androgen concentrations. Casodex-induced elevation of gonadotropin concentrations was less pronounced and serum and testicular levels of androgens did not change significantly. The reduction of seminal vesicle weights was similar after Casodex and GnRH antagonist treatment, whereas flutamide was less effective. Testicular weight and spermatogenesis (assessed by light microscopical and flow-cytometric analysis) remained unaffected by Casodex and flutamide. It is concluded, that 1. Casodex, in contrast to flutamide, is a peripherally selective antiandrogen, and 2. Casodex influences release of gonadotropins into circulation less than flutamide. Therefore this antiandrogen might be useful clinically for selectively blocking androgen actions in the accessory sex glands.

Androgen Antagonists↗