Abstract

The ovarian expression of the endogenous follicle-stimulating hormone β-subunit (FSHβ) and common α-subunit (Cα) genes, and a herpes simplex virus thymidine kinase (tk) transgene, driven by a 2·3 kb bovine FSHβ promoter, was studied in normal and transgenic (tg) mice. tk functions not only as a neutral reporter that enables the study of the promoter function but also as an exogenously inducible toxigene. Reverse transcriptionPCR followed by Southern blot hybridization with a nested probe was used to show the expression of the gene at the mRNA level. Common α-subunit mRNA was detected in the pituitary gland and ovaries of normal adult mice. We have previously detected endogenous FSHβ and tg tk mRNAs in the mouse pituitary, testis and ovary. In this study, the cellular localization of the corresponding proteins was visualized by immunocytochemistry. In normal mouse ovaries a positive reaction with FSHβ and Cα antisera was seen in some of the corpora lutea and most prominently in the interstitial cells. A positive reaction with the tk antiserum was seen in the same cell types of tg mouse ovaries, but not in those of non-tg mice. Cell-ablation-inducing treatment (gancyclovir, 20 mg/kg per day, for 14 days) of tg female mice reduced pituitary FSH concentrations by 52% (P<0·05) but did not affect pituitary LH or plasma gonadotropins compared with non-tg females treated in the same way. A longer period of cell ablation induction (acyclovir 400 mg/kg per day, for 21 days) reduced not only pituitary but also plasma FSH concentrations (55 and 57% respectively; P<0·05) without affecting LH. This treatment also reduced ovarian weight by 38% (P<0·01). In conclusion, our results show first that the endogenous FSHβ and Cα proteins are produced in the mouse ovary. Hence, endogenously synthesized FSH or its subunits may have a role in the paracrine regulation of ovarian function. Secondly, the FSHβ promoter directs the expression of tg tk in the pituitary gonadotrope cells, as shown by specific but partial ablation of FSH-producing cells after induction by gancyclovir and acyclovir. In the ovary, tk protein was localized to the same compartments as the endogenous gonadotropin subunit proteins. This further confirms our finding of ovarian expression of the FSH subunit genes.

Journal of Endocrinology (1996) 150, 265–273

We have developed a transgenic (TG) mouse model for tumorigenesis of gonadal somatic cells using a 6 kb fragment of the mouse inhibin-alpha subunit promoter (Inh-alpha) fused with the simian virus 40 T-antigen (Tag) coding sequence. Gonadal tumors, of Leydig or granulosa cell origin, develop in the TG mice with 100% penetrance by the age of 5-8 months. Conspicuously, if the mice are gonadectomized, they develop adrenal tumors. Gonadal and adrenal tumorigenesis in these mice seem to be gonadotropin dependent. On the other hand, testosterone stimulates the proliferation of a cell line (C alpha 1) established from one of the adrenal tumors. The purpose of the present study was therefore to investigate further whether testosterone affects the growth of these gonadal and adrenal tumors in vivo. Two experimental models were used: (1) Tag TG/hypogonadotropic (hpg) double mutant mice and (2) castrated Tag TG mice. Both were treated between 1-2 and 7-8 months of age with Silastic rods (length 2 cm) containing testosterone. None of the control or testosterone-treated Tag/hpg mice developed gonadal or adrenal tumors. The castrated Tag TG mice displayed, upon microscopical examination, early stages of adrenal tumors, whereas those receiving testosterone did not show such changes. Testosterone increased the weights of gonads in the Tag/hpg mice, and those of uteri and seminal vesicles in both groups. In contrast, the adrenal weights were significantly reduced in both groups by testosterone treatment. Gonadal histology of the testosterone-treated mice showed hyperplasia of testicular Leydig cells and ovarian stroma. Spermatogenesis was induced by testosterone in the Tag/hpg mice. Adrenal histology of the testosterone-treated animals demonstrated the disappearance of the X-zone. Serum levels of FSH in testosterone-treated Tag/hpg mice were significantly increased, while those of serum LH were decreased. In conclusion, the present result indicate that the suppression of gonadotropins by testosterone implants in castrated Inh-alpha/Tag TG mice prevents the tumorigenesis of their adrenals. In intact Tag/hpg mice, testosterone implants were not able to induce gonadal or adrenal tumorigenesis. Although testosterone treatment was able to induce interstitial cell hyperplasia in gonads of the Inh-alpha/Tag mice, direct gonadotropin action is responsible for gonadal and adrenal tumorigenesis.

ABSTRACT

Serum samples from healthy men (n = 6), perimenopausal women (n=9) and patients with polycystic ovarian disease (n = 4) were analysed for LH bioactivity by the two widely used in-vitro bioassay systems: the mouse and rat interstitial cell testosterone-formation assays. The results were compared with an assay employing LH-stimulated cyclic AMP production by cultured human granulosa-luteal cells. Average bioactive LH levels in the mouse cell assay were 1·6-fold higher than those measured using the rat assay. A good correlation (r = 0·89, P<0·01) was observed between the bioactive LH levels measured by these two assays. No significant difference was found between the sensitivities of the two assays: 0·009 ±0·003 IU/1 (mean ± s.e.m., n=10) with rat cells and 0·011±0·003 IU/1 (n=10) with mouse cells. The LH level resulting in half-maximal stimulation of testosterone production in the mouse model was twofold higher than that in the rat model (0·185 ±0.020 vs 0·083 ±0·022 IU/1, P<0·01). The bioactive LH levels measured by the human granulosa-luteal cell assay averaged 12% higher than those obtained with the rat assay (r =0·84, P<0·01), but 58% lower than levels measured with the mouse assay (r = 0·86, P<0·01). The data indicate that the target cell model used in the in-vitro bioassay of LH contributes to the documented discrepancies in reports on serum levels of bioactive LH. Although good correlations were found between all assay systems, the absolute levels of LH bioactivity measured with the rat assay are closer than mouse data to levels measured with a homologous bioassay employing human granulosa-luteal cells.

Journal of Endocrinology (1991) 128, 131–137

Abstract

The mode of FSH actions within the testis was studied in immature hypophysectomized male rats by treatment with recombinant human FSH (recFSH, Org 32489). To elucidate the involvement of Leydig cells and androgens in the maintenance of spermatogenesis in FSH-treated hypophysectomized rats further, the recFSH treatment was given both alone and after destruction of Leydig cells with ethane-1,2-dimethane sulphonate (EDS). Three days after hypophysectomy (at 31 days of age) the rats were given one i.p. injection of vehicle or EDS and, 4 days later, they were implanted with osmotic minipumps releasing either 0·9% (w/v) NaCl or 1 IU recFSH/day.

Recombinant FSH alone increased testicular weights 2·5-fold in 7 days (P<0·01). The effect of FSH was similar in EDS-pretreated rats (P<0·01). Testicular testosterone increased from 6·5 ± 1·6 to 16·9 ± 5·3 (s.e.m.) pmol/g tissue (P<0·05) and serum testosterone from 0·12 ± 0·02 to 0·22 ± 0·03 nmol/l (P<0·05) when the rats were treated with recFSH. EDS alone did not affect testicular testosterone but, when combined with recFSH, it totally abolished the stimulatory effect of FSH on testosterone. Testicular binding of ¹²⁵I-labelled iodo human chorionic gonadotrophin (hCG) and ¹²⁵I-labelled iodo recFSH was increased 2·5- and 2·1-fold respectively with recFSH treatment (P<0·01). EDS, either alone or with FSH, abolished specific testicular hCG binding (P<0·01), but had no effect on that of recFSH. However, FSH increased its own receptors only in animals not treated with EDS.

Histological analysis of the testes revealed that the diameters of the seminiferous tubules increased from 115 ± 6·1 to 160 ± 7·2 μm (P<0·05) with recFSH, and a comparable increase was observed when EDS treatment preceded that of recFSH (143 ± 1·5 μm, P<0·05 vs. controls). Quantification of the spermatogenic cells indicated that recFSH supported the progression of spermatogenesis, as shown by increased number of meiotic and haploid spermatogenic cells (P<0·05). In all EDS-treated animals, spermatogenesis was severely disturbed and only a few spermatids were seen.

In conclusion: (1) these results further support the suggestion that FSH has indirect stimulatory effects on Leydig cell function, (2) the completion of meiosis and spermiogenesis are supported by FSH, the effect of which is enhanced by the presence of Leydig cells, suggesting its dependence on androgens, and (3) we show for the first time that FSH is able to stimulate its own receptors only in the presence of Leydig cell-derived factors, probably androgens.

Journal of Endocrinology (1994) 141, 449–457

ABSTRACT

Direct effects of testosterone on gonadotrophins at the pituitary level were studied in intact and castrated immature (age 10 days) and mature (70 days) male rats. Gonadotrophin-releasing hormone action was blocked by treatment with a potent GnRH antagonist, Ac-d-pClPhe-d-pClPhe-d-Trp-Ser-Tyr-d-Arg-Leu-Arg-Pro-d-Ala-NH₂CH₃COOH (Ant; Organon 30276; 1·0 mg/kg body weight per day) injected subcutaneously. Silicone elastomer capsules were used for the testosterone treatment. Both treatments commenced on the day of orchiectomy and lasted for 7 days. In adult male rats Ant treatment suppressed serum testosterone from 9·5 ± 2·5 (s.e.m.) nmol/l to below the limit of detection (< 0·10 nmol/l; P < 0·01), and the testosterone implants reversed the decrease. Treatment with Ant decreased the pituitary content of FSH-β subunit mRNA in intact and orchiectomized rats to 14% of their respective controls (P < 0·01). These levels were increased to 80–81% of controls (not significant) in both groups by combined treatment with testosterone and Ant. Orchiectomy alone increased FSH-β subunit mRNA by 202% (P < 0·01). In intact immature rats Ant treatment decreased the level of pituitary FSH-β subunit mRNA to 21% (P<0·01), and a partial recovery (P < 0·01) to 42% of controls was observed with combined Ant + testosterone treatment. In contrast, in orchiectomized immature rats, where ANT decreased FSH-β subunit levels to 48% of controls (P < 0·01), testosterone was able to reverse these mRNA levels completely (114% of controls). No evidence for the direct pituitary effects of testosterone were found in the mRNA of the common α or LH-β subunits. In adult rats, the testicular inhibin α and β_A subunit mRNA levels were increased (P < 0·01) by Ant + testosterone compared with Ant-treated animals, but there were no differences in serum immunoreactive inhibin between any of the uncastrated adult groups. In intact immature rats, Ant + testosterone treatment increased (P < 0·01) inhibin β_A subunit mRNA levels compared with controls and Ant-treated animals. Ant decreased the level of peripheral inhibin immunoreactivity from 8·3 ± 2·0 U/ml to 2·1 ± 0·4 U/ml (P < 0·01) and testosterone reversed it to 5·8 ± 0·6 U/ml (not significant).

In conclusion, our observations indicated that testosterone is able to stimulate FSH gene expression and secretion directly in immature and adult rats, but the testosterone response is enhanced at both ages by orchiectomy, even more so in the immature rat. This may be explained by age differences in the contribution of testicular inhibin to the regulation of FSH synthesis and secretion at the pituitary level.

Journal of Endocrinology (1993) 137, 69–79

Abstract

The prolactin receptor (PRLR) is a member of the cytokine/prolactin/GH receptor family, and it is widely expressed in various mammalian tissues. Expression of the two different forms of PRLR, differing in the length of their cytoplasmic domains, was studied in rat gonads during fetal and postnatal development. The two forms of PRLR mRNA were analyzed by reverse transcription (RT)-PCR using primer pairs specific for the different forms. The specificity of the cDNA species generated by RT-PCR was verified by Southern hybridization using nested ³²P-labeled oligonucleotides. The results indicated that both forms of PRLR mRNA are expressed in the rat testis and ovary, which is in agreement with previous reports. The onset of expression of the two PRLR forms occurs on day 14·5 of fetal life in rat testis. In the ovary, the long form of PRLR mRNA appears 1 day before the short form, i.e. these forms begin to be expressed on fetal days 14·5 and 15·5 respectively. In situ hybridization with antisense cRNA probes specific to each form of the PRLR mRNAs demonstrated specific hybridization of both forms, localized in Leydig cells from day 18·5 of fetal life and at the postnatal ages studied. Compared with our previous findings concerning the ontogeny of LH receptor gene expression, PRLR gene expression starts earlier in development and exhibits no sexual dimorphism. The presence of two forms of PRLR mRNA in the fetal gonads suggest that they might play differential roles in gonadal development and function.

Journal of Endocrinology (1995) 147, 497–505

In the rat, the cytotoxic drug ethylene dimethane sulfonate (EDS) selectively eliminates mature Leydig cells (LCs) from testicular interstitium, activating a complex process of proliferation and differentiation of pre-existing LC precursors. We observed previously that after EDS treatment, the early LC precursors persistently express a truncated 1.8 kb form of LH receptor (LHR) mRNA. This prompted us to study whether experimental cryptorchidism, known to alter the process of LC repopulation, can influence the pattern of testicular LHR mRNA expression after EDS administration. EDS treatment completely eliminated mature LCs both in control and unilaterally cryptorchid (UC) rats. This response was followed by gradual reappearance of newly formed, functionally active LCs, as evidenced by the recovery in testicular LHR content and plasma testosterone levels in both experimental groups. Noteworthy, the rate of LC repopulation was higher in the abdominal testes of UC rats, in keeping with previous findings. Interestingly, the 1.8 kb LHR transcript was persistently expressed in scrotal testes at all time-points, but undetectable upon Northern hybridization in abdominal testes at early stages after EDS administration, when low levels of expression of truncated LHR transcripts could only be detected by semi-quantitative RT-PCR analysis. In addition, the faster LC repopulation in cryptorchid testes was associated with precocious recovery of the complete array of LHR mRNA transcripts, including the 1.8 kb species. These changes appeared acutely and irreversibly, as unilateral positioning of scrotal testes into the abdomen resulted in a rapid loss of expression of the 1.8 kb LHR transcript, whereas scrotal relocation of the UC testes failed to alter the pattern of LHR gene expression. In conclusion, experimental cryptorchidism changes the pattern of LHR mRNA expression in rat testis after selective LC destruction by EDS. This change, i.e. repression of the 1.8 kb LHR transcript after EDS administration, is acute and irreversible, and likely related to the impairment of testicular microenvironment following cryptorchidism. However, even though at low levels, the expression of truncated forms of LHR mRNA appears to be a universal feature of proliferating LC precursors. The UC testis may represent a good model for analysis of the regulatory signals involved in the control of LHR gene expression.

Abstract

Stage-specific expression of the FSH receptor (FSHR) gene in the rat seminiferous epithelium was studied. Using transillumination-assisted microdissection for sample preparation and Northern hybridization for analysis of total RNA, we first reassessed the stage specificity of the FSHR gene expression in the adult rat testis. Sixfold higher FSHR mRNA levels were found in stages XIII–I compared with stage VI of the seminiferous epithelial cycle, which had the lowest signal level (P<0·01). The other stages had intermediate signal levels. In situ hybridization showed distribution of grains which confirmed the data obtained by Northern analysis. Prepubertal stage-specific FSHR gene expression was studied using in situ hybridization. Stage specificity could first be demonstrated at the age of 16 days when the average grain counts in stages I–IV were threefold higher than in stages VI–VII (P<0·01). The present data are in agreement with earlier findings on stage-specific FSH binding and FSHR gene expression using both microdissected and stage-synchronized seminiferous tubules. The onset of stage-specific FSHR gene expression is concomitant with maturation of the Sertoli cell population and completion of the first generation of spermatocytes. This supports the hypothesis that spermatogonia and spermatocytes may be involved in the regulation of FSHR gene expression.

Journal of Endocrinology (1996) 151, 29–35

Abstract

The effects of 3-week treatment with increasing doses of epitestosterone (ET) on gonadotrophin gene expression and secretion, on testosterone and 5α-dihydrotestosterone (DHT) levels, and on the weight of testes and prostates, were studied in intact adult male rats. The hormones were delivered by means of silastic capsules of different lengths filled with the steroid. One group of rats received testosterone (T) instead of ET, to compare the results with previous studies concerning the testosterone effect. The controls were given capsules with glucose only. Treatment with ET, as well as with T, significantly reduced the weights of prostates. When the data from ET-treated rats and controls were combined, a significant negative correlation (P<0·001) was found between the weight of prostates and serum ET. T, in contrast to ET, also decreased significantly the weights of testes. ET treatment caused a significant reduction of serum T levels but only an insignificant decline of DHT levels, independent of the dose. Serum and pituitary (p) luteinizing hormone (LH) levels in the ET-treated rats did not change. Pituitary mRNA contents for the βLH subunit (βLH-mRNA) showed a dose-dependent significant increase, up to 170% (P<0·01), with ET treatment. pFSH decreased with the lowest ET (2 cm) dose (P<0·05), but no change was observed with the other doses. The mRNA for the common α-subunit also increased with the ET load. In conclusion, ET acts at several sites in the regulation of gonadotrophin formation and release. It enhances the steady-state mRNA levels of both gonadotrophins in the pituitary. At the same time, ET may act directly in the pituitary by inhibition of post-transcriptional events in LH synthesis. A direct inhibitory effect of ET at the hypothalamic level is also possible. The circulating levels of both gonadotrophins are thus the result of these composite effects.

Journal of Endocrinology (1994) 143, 353–358

The biological actions of estrogens on target cells are mediated by two nuclear receptors: the estrogen receptor (ER) alpha and the recently characterized ER beta. In the male rat, the physiological role of estrogens involves multiple actions, from masculinization of brain areas related to reproductive function and sexual behavior to regulation of testicular development and function. Paradoxically, however, administration of high doses of estrogen during the critical period of neonatal differentiation results in an array of defects in the reproductive axis that permanently disrupt male fertility. The focus of this study was to characterize the effects and mechanism(s) of action of neonatal estrogenization on the pattern of testicular ER alpha and beta gene expression during postnatal development. To this end, groups of male rats were treated at day 1 of age with estradiol benzoate (500 microg/rat), and testicular ER alpha and ER beta mRNA levels were assayed by semi-quantitative RT-PCR from the neonatal period until puberty (days 1-45 of age). Furthermore, the expression of androgen receptor (AR) mRNA was evaluated, given the partially overlapping pattern of tissue distribution of ER alpha, ER beta and AR messages in the developing rat testis. In addition, potential mechanisms for neonatal estrogen action were explored. Thus, to discriminate between direct effects and indirect actions through estrogen-induced suppression of serum gonadotropins, the effects of neonatal estrogenization were compared with those induced by blockade of gonadotropin secretion with a potent LHRH antagonist in the neonatal period. Our results indicate that neonatal exposure to estrogen differentially alters testicular expression of alpha and beta ER messages: ER alpha mRNA levels, as well as those of AR, were significantly decreased, whereas relative and total expression levels of ER beta mRNA increased during postnatal/prepubertal development after neonatal estrogen exposure, a phenomenon that was not mimicked by LHRH antagonist treatment. It is concluded that the effect of estrogen on the expression levels of ER alpha and beta mRNAs probably involves a direct action on the developing testis, and cannot be attributed to estrogen-induced suppression of gonadotropin secretion during the neonatal period.