[TGF beta (transforming growth factor beta) and its related peptides in the local control of the testicle]

Recent data on TGF beta (and related peptides) expression and action in the testis are briefly reviewed. At least, three isoforms of TGF beta are expressed during the male gonadal development. TGF betas are expressed in somatic and germ cells. The expression of the different isoforms varies during gonadal development and is cell specific. Both types I, II and III TGF beta receptors have been localized in somatic cells. TGF beta inhibits gonadotropin action both in Sertoli cells and Leydig cells as well as proliferation of germ cells and Leydig cells. Inhibins and activins (in terms of mRNA and proteins) are expressed in somatic cells and germ cells. Inhibin production in Sertoli cells is under the control of FSH, local factors (ex: EGF, insulin, opiods) and probably of germ cells. Activins and inhibins regulate Leydig and Sertoli cells activities and germ cells development. The existence of activin receptors in somatic and germ cells has been suggested by the presence of type II receptor mRNA (ActRII and ActRIIB).

In vivo and in vitro studies on the differential role of luteinizing hormone and follicle-stimulating hormone in regulating follicular function in the bonnet monkey (Macaca radiata) using specific gonadotropin antibodies

Although a distinct need for FSH in the regulation of follicular maturation in the primate is well recognized, it is not clear how FSH controls the functionality of different cellular compartments of the follicle. It is also not evident whether there is a requirement for LH in follicular maturation in the primate. In the first part of the present study, female bonnet monkeys were administered a well-characterized ovine (o) LH antiserum to neutralize endogenous monkey LH for different periods during the follicular phase, and the effect on the overall follicular maturation process was assessed by analyzing serum estrogen (E) and progesterone (P) profiles. Neither continuous LH deprivation from Day 8 of the cycle nor deprivation of LH on any one day between Days 6 and 10 had a significant effect on serum E and P profiles and the follicular maturation process. The period for which the antiserum was effective was dependent upon the dose injected; 1 ml of the antiserum given on Day 8 blocked ovulation but not follicular maturation. To assess the effect of deprivation of LH/FSH at the cellular level, animals were deprived in vivo of LH (on Days 8 and 9 of the cycle) or of FSH (on Day 6 of the cycle) by injection of highly characterized hCG and ovine (o) FSH antisera, respectively; the in vitro responsiveness of granulosa and thecal cells isolated on Day 10 from these animals was then determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormone sensitivity of germ cells in stage XIV and in stage I of the rat spermatogenic cycle

Previous data have been inconclusive with respect to whether the meiotic degenerations that occur in stage XIV of the spermatogenic cycle are increased after hypophysectomy. Meiotic cell degenerations in Stage XIV and early Stage I of the spermatogenic cycle were enumerated to determine if the advanced generation of meiotic cells were influenced by hormonal deprivation subsequent to hypophysectomy and, if so, could cellular degenerations be prevented by supplementation with either testosterone or recombinant FSH during the period of hypophysectomy. The animals utilized were either pituitary-intact rats or rats hypophysectomized for 3 or 10 days. Hormone supplementation began at day 3 post-hypophysectomy and continued until day 10 at which time all animals were sacrificed. The numbers of degenerating meiotic figures (metaphase to telophase of the first and second meiotic division) as expressed per Sertoli cell nucleus or nucleolus were not increased significantly 10 days after hypophysectomy as compared with animals hypophysectomized for 3 days or with pituitary-intact controls. Exogenously administered testosterone and FSH had no effect on the numbers of degenerating meiotic germ cells in hypophysectomized animals. These data indicate that stage XIV metaphase to telophase spermatocytes are not hormone sensitive. However, it was determined that there were new cell types degenerating at Stage XIV and I of the spermatogenic cycle. These were interphase secondary spermatocytes and step 1 spermatids and were seen in stages XIV and I, respectively. These cell degenerations were found in low numbers in Stage XIV and I in either FSH-treated or testosterone-treated rats, suggesting their hormone sensitivity. Thus it is possible that Stages XIV and I are hormone sensitive stages.(ABSTRACT TRUNCATED AT 250 WORDS)

[The inhibitory effect and its mechanism of transferrin on FSH-induced differentiation of granulosa cells]

Transferrins are a class of related metal-binding transport glycoproteins for transporting iron to various organs and tissues of the body. In recent years, it has been reported that the transferrin can play an important role in the local regulation of ovarian function, apart from its iron-binding characteristic. Transferrin could attenuate FSH-induced differentiation of rat and human granulosa cells and its mechanisms were considered as follows: (1) Transferrins partially blocked the binding of FSH with its receptors on granulosa cells and reduced the formation of intracellular cAMP, and therefore inhibited the expression of FSH receptors. (2) Acting sites beyond cAMP formation also existed for the inhibitory effect of transferrin on inhibin and estradiol production. (3) The inhibitory effect of transferrin seemed not to be involved in the changes of protein kinase C activity, the calcium release and "proliferation-differentiation reversed mechanism" in granulosa cells.

[Recent findings concerning follicular growth]

Recent advances in molecular genetics now enable the study in vitro of follicular maturation using human recombinants of gonadostimulins (FSH and LH) and certain autocrine and paracrine ovarian regulation factors. This is leading to reevaluation of the precise role played by the various hormonal protagonists of folliculogenesis. FSH, in the presence of low levels of LH at the start of the follicular phase, has a mitotic action on estrogen-producing granulosa cells, encourages their differentiation and activates the synthesis of their genetically-determined products (essentially somatomedin, inhibin and activin) and of the LH receptor. High LH levels, during the second half of the follicular phase, stop proliferation of granulosa cells, and, synergistically with insulin-like growth factor 1, bring about an increase in estrogen synthesis from aromatisable androgens. In common with FSH, LH facilitates the production of cybernins and of essential growth factors, as well as of preovulatory progesterone. Abnormalities of endocrine, paracrine or autocrine regulation of follicular maturation may lead to atresia. Future rational uses of human FSH and LH are obvious and involve the optimisation of ovulation induction and in vitro fertilisation in sterile women.

Follicular oestrogen synthesis: the 'two-cell, two-gonadotrophin' model revisited

The original 'two-cell mechanism' explained the endocrine regulation of follicular oestrogen synthesis and implied paracrine signalling in the follicle wall. It is now known that the CYP17 gene encoding 17-hydroxylase/C17-20-lyase activity crucial to androgen synthesis, is expressed exclusively in thecal cells. 17-Hydroxylase/C17-20-lyase activity is regulated by LH and subject to local modulation by a factor(s) emanating in FSH-stimulated granulosa cells. The FSH receptor gene is expressed exclusively in granulosa cells, where FSH acts directly to induce cytoproliferation and differentiation via cyclic AMP/protein kinase-A mediated post-receptor signalling. Granulosa cells also express androgen receptors, and theca-derived androgen has the potential to modulate locally differentiative responses to FSH. When follicles are recruited to preovulatory development by FSH, their granulosa cells develop LH receptors functionally coupled to aromatase activity and inhibin production. Thereby they simultaneously undertake LH-responsive aromatization and inhibin synthesis. Inhibin has the potential to potently enhance LH-stimulated thecal androgen synthesis. Granulosa-derived inhibin may therefore participate in a paracrine mechanism that locally amplifies androgen synthesis, and hence oestrogen formation, in the preovulatory follicle(s).

Effects of castration and recombinant human inhibin administration on circulating levels of inhibin and gonadotropins in adult male monkeys

Inhibin has been suggested to play a role in gonadal feedback regulation of follicle-stimulating hormone (FSH) secretion; however, neither the half-life nor the time course of action of recombinant inhibin has been reported in any primate species. We sought to determine the disappearance half-life of circulating endogenous inhibin following castration in adult male monkeys, Macaca fascicularis, and to determine the half-life of administered recombinant human inhibin A and its effect on bioactive FSH and luteinizing hormone (LH) levels in castrate monkeys. Endogenous inhibin fell from 8,122 +/- 2,077 U/L (mean +/- SEM, n = 5) prior to castration to 383 +/- 84 U/L at 24 hours and 269 +/- 44 U/L at day 21 (P < 0.05 at 24 hours vs. day 21) (detection limit of assay 234 U/L). The early phase half-life of endogenous inhibin was 34 minutes (between 8 and 60 minutes) and a later phase half-life of 75 minutes was observed between 1 and 4 hours following castration. Recombinant inhibin exhibited a 14-minute early phase half-life between 8 and 60 minutes following the 5 micrograms intravenous (i.v.) recombinant inhibin dose, and a later phase half-life of 70 minutes between 1 and 4 hours in castrate monkeys (n = 3). Serum inhibin levels were maintained within or above the precastration range for 15 minutes. Single dose recombinant inhibin, 100 micrograms subcutaneous (SC) or intramuscular (IM) administered to castrate monkeys (n = 3), achieved and maintained normal serum inhibin levels for 6 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of FSH in regulating testicular germ cell transformations in the rat: a study using DNA flow cytometry

The role of FSH in regulating testicular germ cell transformations during initiation and maintenance of spermatogenesis in the pubertal and adult rat has been studied using DNA flow cytometry (FCM). The cell types were quantified on the basis of their DNA content using DNA specific fluorochrome DAPI (4,6-diamidino phenylindole). Pubertal (30-d old) and adult (100-d old) rats were deprived of endogenous FSH support for 10 d by daily injection (200 microliters d-1) of a characterized FSH antiserum; the control group received an equivalent volume of normal rat serum. FSH deprivation did not lead to any change in serum testosterone levels. The relative proportion of testicular germ cells in the FSH deprived pubertal rat showed a 90% reduction in 1C (round spermatids) and 260% and 90% increase in 2C (spermatogonia) and 4C (spermatocytes) cells respectively. While the overall conversion of 2C to 1C (1C:2C ratio) was reduced by 98%, the transformation of 2C to 4C (4C:2C ratio) and 4C to 1C (meiotic division 1C:4C ratio) was inhibited by 43% and 93% respectively. In the FSH-deprived adult rat the overall conversion of 2C to 1C was reduced by 26% (P < 0.05) only. The 2C and 4C population of cells increased by 47% and 97% respectively (P < 0.025) and the 4C:2C ratio by 47% (P < 0.05). While the meiotic division (1C:4C ratio) was reduced by 54% (P < 0.001), the post-meiotic differentiation of round spermatids to elongate-spermatids (HC:1C) was inhibited by 68% (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Roles of FSH and testosterone in the initiation of spermatogenesis in prepubertal rats medically hypophysectomized by a GnRH antagonist

Experimentally induced medical hypophysectomy in prepubertal rats through treatment of GnRH antagonist for 3 weeks, initiated on the 20th day of age, markedly decreased testicular weight by 85% of that of the controls. Quantitative assessment of spermatogenesis in testicular semithin preparations revealed a significant reduction in the numbers of preleptotene (27.2 +/- 1.6 to 15.6 +/- 0.52) and pachytene (25.8 +/- 0.96 to 5.35 +/- 0.26) spermatocytes and complete absence of any spermatids after the treatment. By contrast, round stage 7 and elongated spermatids were observed in many tubules of the testis in the age-matched control rats. At the end of GnRH antagonist treatment, the blood levels of LH were undetectable, while testosterone and FSH were decreased to 12 and 44% of the controls, respectively. Supplementation of either FSH (ovine FSH 20 micrograms/rat day-1) or testosterone (30 micrograms/rat day-1) enhanced the testicular weight (68%) and the circulatory levels of these hormones, but failed to support quantitatively normal spermatogenesis, which was, however, qualitatively improved. The number of maturing spermatids were comparatively higher in the testosterone-supplemented group that in the FSH-administered group. The latter group had otherwise the highest number of degenerating germ cells per tubule (mean 4.8 +/- 0.1). Testicular weight and stage-specific germ cell counts were restored to normalcy only in rats supplemented with both FSH and testosterone, the critical concentrations of which were important in the initial stages of spermatogenesis. Testosterone alone had a positive effect in terms of germ cell development, while FSH without testosterone was detrimental to the maturing germ cells.

Current concepts of the roles of follicle stimulating hormone and luteinizing hormone in folliculogenesis

Around 400 follicles sequentially mature and ovulate during an average woman's reproductive lifetime. From birth to the menopause, the other approximately 99.98% of her follicles begin development but never complete it. Instead they default to atresia due to inadequate stimulation by follicle stimulating hormone (FSH). Follicular growth to the stage of antrum formation (approximately 0.25 mm diameter) is independent of gonadotrophic stimulation. Antrum formation and further growth to the stage at which follicles become potentially able to begin preovulatory development (2-5 mm diameter) require tonic stimulation by FSH. Before onset of puberty, blood concentrations of FSH do not rise sufficiently to sustain development beyond this stage, therefore all antral follicles become atretic. After puberty, as each menstrual cycle begins, FSH concentrations rise beyond a critical 'threshold' and multiple follicles are recruited to begin pre-ovulatory development. Due to increases in its responsiveness to FSH and luteinizing hormone (LH), one of these follicles becomes selected to ovulate while the remainder become atretic. At mid-follicular phase, the dominant follicle reaches > or = 10 mm in diameter and increasingly synthesizes oestradiol. Tonic stimulation by FSH and LH, underpinned by local paracrine signalling, maintains oestrogen secretion by the dominant follicle, which grows to > or = 20 mm in diameter before it ovulates in response to the mid-cycle LH surge. The development-related response to LH shown by the pre-ovulatory follicle raises the possibility that exogenous LH might be used as an adjunct to therapy with exogenous FSH in clinical ovulation induction regimens where the aim is to induce monovulation.

Mammalian follicle-stimulating hormone stimulates DNA synthesis in secondary spermatogonia and Sertoli cells in organ culture of testes fragments from the newt, Cynops pyrrhogaster

We previously showed in organ culture of testes fragments from Cynops pyrrhogaster that mammalian follicle-stimulating hormone (FSH) stimulates secondary spermatogonia to differentiate into primary spermatocytes. In this report, we demonstrate in organ culture that FSH stimulates DNA synthesis in secondary spermatogonia and Sertoli cells: the numbers of secondary spermatogonia and Sertoli cells incorporating 5-bromo-2'-deoxyuridine (BrdU) throughout the culture period in the presence of FSH were 3-5 times those incorporating BrdU in the absence of FSH. Moreover, addition of FSH to testes fragments which had become quiescent after a week of culture in the absence of FSH, induced after a day a remarkable increase in the number of spermatogonia and Sertoli cells incorporating BrdU. The above results indicate that FSH stimulates and induces DNA synthesis in spermatogonia and Sertoli cells. Most of the spermatogonia within a cyst were labelled simultaneously and at the same density, indicating that they underwent synchronous DNA synthesis, whereas all the Sertoli cells within a cyst were not labelled simultaneously, indicating that they synthesised DNA asynchronously. When testes fragments pulse-labelled with BrdU were cultured in FSH for 14 days, the secondary spermatogonia differentiated into primary spermatocytes, whereas in the absence of FSH they failed to differentiate and most died by the 7th day. The above results together show that FSH is required for the proliferation of both secondary spermatogonia and Sertoli cells as well as the differentiation of secondary spermatogonia into primary spermatocytes.

Peripheral and local regulators of folliculogenesis

The role of the gonadotrophins follicle-stimulating hormone (FSH) and luteinizing hormone and the putative local regulators, activin and follistatin, in the control of folliculogenesis is reviewed. An account of early work on the development and application of assays for FSH and inhibin is given, together with a summary of the data on the ovarian responsiveness to gonadotrophin and follicular atresia. Models for studying local regulation of granulosa cells in vitro are described and the data from these experiments reviewed. It is concluded that activin has a role in the development and maintenance of healthy oestrogenic follicles, preventing premature luteinization, whereas follistatin opposes these effects of activin and promotes luteinization or atresia.

Lack of between-follicle interactions in the sheep ovary

Follicular growth over 2 mm in diameter is mainly regulated by gonadotrophins (FSH and LH). However, it is possible that between-follicle interactions may be involved in ensuring ovulation of a specific number of follicles. The present study tested specific hypotheses regarding: (1) a stimulatory role of atretic follicles on differentiation of follicles of the next wave; (2) a stimulatory role of large follicles in F-gene-carrier Booroola ewes on differentiation of follicles of the same ovulatory cohort; and (3) an inhibitory role of the dominant follicle on differentiation of follicles of the same ovulatory cohort. The end points measured were aromatase activity (all trials) and granulosa cell proliferation (Booroola). The techniques used tested effects of ovarian venous serum or conditioned media or follicle co-culture. Comparison of the effects of similar protein concentrations of serum or media conditioned by healthy versus atretic follicles could not demonstrate a stimulatory role of the atretic follicle. This was further confirmed using ovarian venous serum draining an ovary bearing an atretic follicle. Comparison of the effects of similar protein concentration of serum or media conditioned by F+ or ++ follicles could not demonstrate a stimulatory role of large follicles in F+ewes. This was supported by the observation that ovarian venous serum of F + or ++ ewes had similar effects on aromatase activity. Furthermore, coculture of small follicles with a large follicle of either genotype did not alter granulosa-cell proliferation compared with controls. This suggests that an alteration in the between-follicles regulation does not operate in Booroola sheep to generate their high ovulation rate. Comparison of the effects of similar protein concentrations of serum, follicular fluid from large follicles or media conditioned by large follicles showed that follicular fluid (but not conditioned media) contained an aromatase inhibitor. This suggests that dominant follicles do not secrete the aromatase inhibitor they contain.

Exogenous steroids and the control of oestradiol secretion by human granulosa-lutein cells by follicle stimulating hormone and insulin-like growth factor-I

This study first examined the relative activities of 17 alpha-hydroxylase, 17,20-lyase and aromatase in human granulosa-lutein cells by challenging the cells with steroid precursors in the oestradiol biosynthetic pathway. When cells from four patients were challenged with precursor steroids on the pathway to oestrogen synthesis (pregnenolone, 17 alpha-hydroxypregnenolone, progesterone, 17 alpha-hydroxyprogesterone and androstenedione at 5 x 10(-6) M), oestradiol (nmol/l) outputs after 1 day of culture were (median, interquartile range) as follows: 4.1 (2.1-8.8; pregnenolone), 3.1 (1.7-6.0; progesterone), 12.5 (6.9-18.1; 17 alpha-hydroxypregnenolone), 8.2 (4.1-16.7; 17 alpha-hydroxyprogesterone) and 251 (140-819; androstenedione). No further increases were seen when the steroid concentration was increased to 1 x 10(-5) M. Basal oestradiol secretion was 3.5 (1.6-8.2) nmol/l. We conclude that the conversion of pregnenolone/progesterone to oestradiol by granulosa-lutein cells is rate limited by 17 alpha-hydroxylase activity but that these cells are capable of oestradiol secretion (in the nmol/l range) in the absence of androstenedione. In the second part of this study we examined the control of granulosa-lutein oestradiol secretion by follicle stimulating hormone (FSH) and insulin-like growth factor-I (IGF-I) in the presence and absence of exogenous androstenedione (10(-6) M). Cells were cultured for up to 6 days and basal oestradiol (nmol/l) fell dramatically over this period both in the presence and absence of androtenedione, e.g. from 339 (223-419) (median and interquartile range, cells from five patients cultured in the presence of androstenedion) after 2 days to 14 (7-59) after 6 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the role of follicle-stimulating hormone and prolactin in the control of testicular endocrine function in adult djungarian hamsters (Phodopus sungorus) exposed to either short or long photoperiod

Exposure of adult male Djungarian hamsters (Phodopus sungorus) to a short photoperiod induces testicular atrophy. To evaluate the role of FSH and prolactin (PRL) in the control of testicular endocrine function, adult Djungarian hamsters were exposed to either a long photoperiod (16L:8D per day) or a short photoperiod (6L:18D per day) for 11 wk. After 11 wk, hamsters housed in each of these photoperiods were placed into three groups and treated s.c. daily for 7 days with 50% polyvinylpyrrolidone in saline (SAL-PVP), rat FSH (10 micrograms/hamster/day) in SAL-PVP, or ovine PRL (100 micrograms/hamster/day) in SAL-PVP. On Day 8, animals in each of these groups received i.p. injections of saline or ovine LH (0.3 microgram/g BW); 1 h later, blood was obtained by cardiac puncture under ether anesthesia. Plasma FSH, LH, PRL, androstenedione (A-dione), and testosterone levels were measured by validated RIAs. In hamsters kept in the short photoperiod, testicular weight was decreased (p < 0.001). In these animals, FSH treatment increased (p < 0.001) testicular weight, whereas PRL injections had no effect. Testicular weight in animals kept in the long photoperiod was unaffected by FSH or PRL treatment. After 12 wk of exposure to the short photo-period, circulating PRL levels were undetectable; plasma levels of FSH (p < 0.001), LH (p < 0.05), A-dione (p < 0.005), and testosterone (p < 0.001) were significantly reduced. Administration of either FSH or PRL had no influence on plasma A-dione levels in hamsters exposed to either photoperiod.(ABSTRACT TRUNCATED AT 250 WORDS)

Oocytes preserve the ability of mouse cumulus cells in culture to synthesize hyaluronic acid and dermatan sulfate

A soluble factor(s) produced by fully grown oocytes is essential, together with follicle stimulating hormone (FSH), to stimulate in vitro hyaluronic acid (HA) synthesis by mouse cumulus cells (CCs). The stability of the response to this stimulus by CCs in culture was investigated. The data showed that preculture for 8 hr in basal medium reduced to approximately 30% the ability of CCs to synthesize HA in response to FSH or dibutyryl cyclic AMP (Bt2cAMP) and soluble oocyte factor(s). However, if CCs were precultured for the same period of time as intact cumulus cell-oocyte complexes, or in the presence of fully grown oocytes, or in medium conditioned by fully grown oocytes, their ability to synthesize HA was 75-95% preserved. In vitro stimulation of dermatan sulfate (DS) synthesis by CCs does not require oocyte factors and is induced by FSH or Bt2cAMP treatment alone. However, the preservation of such activity, like that of HA synthesis, depended on the presence of a soluble oocyte factor(s) during preculture. The presence of isolated oocytes or of oocyte-conditioned medium also prevented the spreading of CCs in culture. However, inhibiting CC spreading by culture on agar-coated plates or in serum-free medium did not preserve their HA or DS synthetic activity, thus suggesting that the two oocyte actions on CCs are independent. Growing oocytes were unable both to induce HA synthesis in freshly isolated CCs stimulated with FSH and to preserve the ability to synthesize HA and DS in 8-hr precultured CCs. The results suggest that the stability of the differentiated state of mouse CCs in vitro depends upon continued exposure to a soluble factor(s) produced by fully grown oocytes.

Follicular development and its control

The female reproductive cycle is based on a co-ordinated function of several regulatory elements and signalling systems. Of the approximately 7 million oocytes present in the human fetal ovary, only 475 will eventually ovulate. In the human, the development of a primordial follicle into a dominant one takes about 10 weeks. Approximately 300 follicles are recruited initially for growth and development, 30 of them are likely to become gonadotropin-dependent and enter competition for dominance and, finally, only one will achieve ovulation. The mechanisms by which follicle stimulating hormone, luteinizing hormone, growth factors and steroids may promote or disrupt follicular development are discussed in detail. Possible implications of these new facts on diagnosis and treatment of ovulatory disturbances are described.

Biological and immunological activities of bovine placental gonadotropin

A bovine placental extract was fractionated on a Concanavalin A (ConA)-Sepharose column into an unadsorbed ConA I fraction and an adsorbed ConA II fraction. The ConA II fraction was then separated by gel filtration on Sephadex G-100 into void volume material (ConA II Sephadex fraction I) and retarded material (ConA II Sephadex fraction II). Con A II Sephadex fraction II was considerably more potent than ConA II Sephadex fraction I in stimulating testosterone production by isolated rat Leydig cells. Con A I fraction was inactive in this regard. None of the aforementioned fractions manifested follicle stimulating hormone (FSH) bioactivity. ConA II Sephadex fraction II yielded a displacement curve parallel to the standard curve in radioimmunoassays for rat luteinizing hormone and thyroid stimulating hormone (TSH), but it did not cross-react in a radioimmunoassay for rat FSH. ConA II fraction did not exhibit FSH bioactivity. The results indicate that bovine placental gonadotropin possesses luteinizing hormone-like bioactivity and immunoreactivity and TSH immunoreactivity but neither FSH bioactivity nor immunoreactivity.

Effects of adenosine analog PIA (n-phenylisopropyladenosine) on FSH-stimulated cyclic AMP (cAMP) production in the rat seminiferous epithelium

In rat seminiferous epithelium, FSH-stimulated cAMP production is cyclically modulated by spermatogenic cells and is highest in stages XIV-V and lowest in stages VII-VIII of the epithelial cycle. Adenosine has been proposed to be an inhibitory paracrine molecule in Sertoli cells. In this paper the effect of adenosine analog n-phenylisopropyladenosine (PIA) on FSH-stimulated cAMP production was studied in staged rat seminiferous tubules. In low responsive stages VII-VIII of the cycle, 100 nM and 10 microM PIA inhibited FSH-stimulated cAMP production by 24% and 28%, respectively. To study whether PIA effect is mediated through Gi-protein, pertussis toxin (PT) pretreatment was used to block the Gi-protein. PT pretreatments of 3 or 18 h caused 42% or 16% elevation in FSH-stimulated cAMP production, respectively. PIA blocked the stimulation caused by PT pretreatment. At 38 days post irradiation, when spermatocytes and round spermatids were decreased in number, in stages VII-VIII of the cycle the inhibitory effect of PIA was abolished. In high responsive stages XIV-V of the cycle, 100 nM PIA stimulated cAMP production by 27%, while 10 microM PIA had no effect. At 38 days post irradiation FSH response was decreased by 19% when compared to non-irradiated level, and PIA stimulated FSH-stimulated cAMP production by 22%. The results suggest that there are stage-specific mechanisms for adenosine-dependent regulation of FSH-stimulated cAMP production in the rat seminiferous epithelium. Advanced spermatogenic cells seem to maintain the mechanisms that include PIA-mediated inhibition of FSH response. Other mechanisms than PT-sensitive Gi-protein seem to be involved in the inhibition.

Hormonal regulation of human testicular inhibin alpha and beta B subunit messenger RNAS

Changes in messenger ribonucleic acids (mRNAs) of human testicular inhibin alpha and beta B subunits induced by human menopausal gonadotropin (hMG) and human chorionic gonadotropin (hCG) were assessed in vivo and in vitro. After a single administration of hMG, inhibin alpha mRNA in the human testis significantly increased, whereas inhibin beta B mRNA remained unchanged. Administration of hCG induced a slight increase in inhibin alpha mRNA without affecting inhibin beta B mRNA. In experiments in vitro using the testicular organ culture technique, an exposure to hMG for 24 hours induced a dose-related significant increase in inhibin alpha mRNA. Inhibin beta B mRNA was not affected by either hCG or hMG exposure. These results indicate that luteinizing hormone (hCG) as well as follicle stimulating hormone (hMG) may play a role in the regulation of human testicular inhibin alpha mRNA, although the mechanism of the LH action is not clear.