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M Parvinen

Publications and source records attributed to M Parvinen.

At least 91 records · Page 5Linked to original sources
PubMed1992

Beta-nerve growth factor influences the expression of androgen-binding protein messenger ribonucleic acid in the rat testis.

The effect of infusion of nerve growth factor (NGF) into the rat testis on the expression of androgen-binding protein (ABP) mRNA was studied. A major 1.7-kb and a minor 3.7-kb ABP mRNA were present at all stages of the seminiferous epithelium with maximal levels at stages VIII-XI and the lowest levels at stages IV-VI. Infusion of 15 ng/h of NGF with a mini-osmotic pump for 14 days resulted in a 2-fold increase of ABP mRNA as revealed by Northern blots, whereas the mRNA level of another Sertoli cell protein, urokinase-type plasminogen activator, remained unchanged. Image analysis of autoradiograms obtained by in situ hybridization of sections from treated testes showed a similar increase in APB mRNA compared to noninfused or PBS-infused testes. However, at the cellular level the labeling intensity for ABP mRNA over Sertoli cells of different stages of the seminiferous epithelium was the same in NGF-infused and control testes. This suggests that the increase of ABP mRNA in NGF-infused testes was caused by prolongation of stages VII-VIII with maximal ABP mRNA expression; the suggestion is supported by an increase of 30 percent in frequency of these stages in histological sections from NGF-infused testes.

Androgen-Binding Protein↗
PubMed1992

Insulin-like growth factors selectively stimulate spermatogonial, but not meiotic, deoxyribonucleic acid synthesis during rat spermatogenesis.

The in vitro effects of insulin-like growth factor-I (IGF-I), insulin-like growth factor-II (IGF-II), truncated IGF-I, insulin, and human GH (hGH) on premitotic and premeiotic DNA synthesis of adult rat germ cells in vitro were investigated. Two-millimeter segments of seminiferous tubules from four different stages containing type A4-spermatogonia (stage I), type B spermatogonia (stage V), resting preleptotene spermatocytes (stage VIIa), and preleptotene spermatocytes in the S-phase (stage VIII-IX), respectively, were isolated by transillumination-assisted microdissection. They were cultured in serum-free medium at 34 or 37 C with and without growth factors, labeled for 4 h with tritiated thymidine, and harvested at 24, 48, and 72 h. Spontaneous progression of spermatogenesis was noted at both incubation temperatures, with a more rapid rate at 37 C. IGF-I significantly stimulated [3H]thymidine uptake in originally stage I and stage V tubule segments (type A4 and B spermatogonia, respectively) after 48 h of culture at 37 C. Improved maintenance of the DNA synthesis of stage VIII-IX tubules was found after 48 h at 37 C and 72 h at 34 C. Truncated IGF-I produced a similar response, but was more potent. IGF-II showed slight stimulation of stage V tubules after 72 h at both 34 and 37 C and maintenance of stage VIII-IX tubules after 48 h at 37 C and 72 h at 34 C. hGH was effective only at 34 C, showing slight stimulation of stage I tubule segments after 48 and 72 h of incubation. Insulin at high concentrations was effective only at 37 C and stimulated DNA synthesis in stages I, V, and VIIa after 48 h and stages V and VIIa after 72 h of incubation. It is concluded that IGFs stimulate premitotic DNA synthesis of rat germ cells in vitro and may also maintain premeiotic DNA synthesis. Whether the slight response to hGH is mediated via local production of IGF-I by the tissue cultures remains to be investigated. As IGF-I and IGF-II are locally produced in the testis, the present results suggest that these factors have a selective paracrine or autocrine role in the regulation of spermatogonial proliferation during spermatogenesis.

Animals↗
PubMed1992

Expression of inhibin beta A and beta B, follistatin and activin-A receptor messenger ribonucleic acids in the rat seminiferous epithelium.

The expression of inhibin beta A and beta B subunits, follistatin, and activin-A receptor messenger RNA (mRNAs) in different stages of rat seminiferous epithelial cycle was analyzed by in situ hybridization in order to understand their role in the regulation of spermatogenesis. Inhibin beta A mRNA was expressed in Sertoli cells in a highly stage-specific manner. The mRNA levels started to accumulate in Sertoli cells at stage VIII of the cycle and were highly expressed during stages IX-XI. Follistatin mRNA expression was identical to that of inhibin beta A, while inhibin beta B mRNA was maximally expressed in Sertoli cells at stages XIII-III. Low expression was found in stages VII-VIII. Activin-A receptor mRNA was localized mainly in spermatogenic cells. Maximal expression was seen in late primary spermatocytes at stages XIII-XIV and in early round spermatids at stages I-IV. A low even expression by Sertoli cells was also seen. Inhibin beta A and follistatin mRNAs were coexpressed in stage IX-XI Sertoli cells, suggesting close interplay between these molecules. The pattern of inhibin beta B mRNA expression was similar to that of inhibin alpha-mRNA. Localization of activin-A receptor mRNA in spermatogenic cells suggests that activin may influence meiotic divisions and early spermiogenesis.

Activin Receptors↗
PubMed1991

Stage- and cell-specific gene expression and hormone regulation of the seminiferous epithelium.

The regulation of spermatogenesis seems to involve complex cell interactions in the testis. Little is known about these cellular communication events. Advances in molecular technology and cell or cell group separation methods have made it possible to analyze function of defined spermatogenic and Sertoli cells, thereby giving some insights into the paracrine regulation of spermatogenesis. In this review we will describe how seminiferous tubule segments with distinct cell associations can be rapidly isolated and how the cell composition can be modified by high-energy X-irradiation. Results of the recent studies performed using these techniques will be briefly summarized. Spermatogenic cells at defined stages of their development can be isolated in living condition for morphological and biochemical studies by the transillumination technique. For accurate identification of the stages of the seminiferous epithelial cycle, phase contrast microscopy of live cell squashes has been used. The criteria described by Leblond and Clermont (Am. NY Acad. Sci., 55:548-573, 1952) can be used for accurate recognition of most of the stages of the cycle. However, stages I and II and substages of VII that are important in several studies are difficult to distinguish. Therefore, in addition to the morphology of early spermatids, development of the flagella at step 16 of spermiogenesis and the changing morphology of the cytoplasmic lobes (residual bodies) at stage VII of the cycle were used as criteria for rapid identification and isolation (preparative) of the seminiferous tubule segments. Expression of nucleoprotein and heat shock protein 70-related protein genes was analyzed with Northern blot, slot blot, and in situ hybridization techniques in accurately staged seminiferous tubules. Accurate stage-dependent timing of the onset of transcription, followed by storage and disappearance of the messages was demonstrated. The chromatoid body (cb) has been proposed to have a specific function in storage of the long-lived mRNAs in the spermatids. It is an actively moving cytoplasmic organelle that interacts with Golgi complex during formation of the acrosomic system. The chromatoid body is apparently also dependent on cytoplasmic microtubules, since its movements are inhibited and its structure becomes abnormal in the presence of vincristin, an inhibitor of tubulin polymerization. Follicle-stimulating hormone (FSH) is an important regulator of Sertoli cell function. Since both basal and FSH-dependent cyclic AMP (cAMP) production by seminiferous tubules showed marked stage dependency, Sertoli cells are apparently influenced by spermatogenic cells. Thus, Sertoli cell function varies cyclically depending on the stage of the seminiferous epithelial cycle to provide an optimal microenvironment for spermatogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Testicular toxicity and mutagenicity of steroidal and non-steroidal estrogens in the male mouse.

The mutagenicity and toxicity of diethylstilbestrol (DES), 17 beta-estradiol and zeranol on the male mouse germ cells were investigated with meiotic micronucleus assays in vivo and in vitro, sperm-head abnormality test and morphometry. Further, the developmental effects of DES on testicular morphology were explored. Micronucleus induction was observed at 10(-7) M concentration of DES and 17 beta-estradiol in vitro, but other treatments yielded negative results. The micronucleus assay in vivo revealed a small number of micronuclei in early haploid spermatids 17 days after a single subcutaneous injection of DES 50 mg/kg, whereas estradiol and zeranol gave negative results. The sperm-head abnormality rates were significantly elevated 5 weeks after treatments with high doses of DES, 17 beta-estradiol and zeranol, and testicular morphometry revealed transient changes in the volume densities of testicular tissue components. Prenatal and neonatal estrogen administration resulted in permanent alterations in seminiferous epithelium and dilatation of the rete testis, but did not affect micronucleus or sperm-head abnormality rates. The mutagenicity and toxicity of hormones in the mouse testis paralleled the hormonal activity of these compounds. Early estrogenization was the most sensitive toxicity test, followed by in vitro meiotic micronucleus induction, whereas the sperm-head abnormality assay and morphological analysis did not reveal subtle changes.

Animals↗
PubMed1991

Stage-specific cellular regulation of inhibin alpha-subunit mRNA expression in the rat seminiferous epithelium.

To find out the local regulation of inhibin production and its possible paracrine role in the seminiferous epithelium, inhibin alpha mRNA levels were measured in sequential 1 mm segments of rat seminiferous tubules accurately staged by transillumination technique. Highest levels were found at stages XIV-I-IV of the cycle, and lowest at stages VI-VIIb of the cycle. When dividing spermatogonia were selectively destroyed by 3 Gy of high-energy X-irradiation, stage-specific inhibin alpha mRNA levels remained unchanged until 26 and 38 days after irradiation when stages VII and VIII of the cycle showed 6- and 4-fold increases during a selective reduction of pachytene spermatocyte and round spermatid numbers, respectively. The results suggest that these cells at a strictly stage-specific fashion have a paracrine inhibitory effect on Sertoli cell inhibin alpha gene expression. Inhibin alpha mRNA level also correlates closely to the follicle-stimulating hormone-stimulated cAMP production during the cycle of the seminiferous epithelium, but does not seem to have a correlation to spermatogonial DNA synthesis.

Animals↗
PubMed1991

Production and secretion of an interleukin-1-like factor is stage-dependent and correlates with spermatogonial DNA synthesis in the rat seminiferous epithelium.

It has been shown previously that the intact adult rat testis produces large amounts of an interleukin-1 (IL-1)-like growth factor. The present study has investigated whether this testicular IL-1-like factor (tIL-1) is produced and secreted differentially by the fourteen stages of the seminiferous epithelial cycle in the rat testis. Seminiferous tubule segments representing defined stages were identified by transillumination-assisted microscopy and isolated by microdissection. Pooled segments were either homogenized and extracted with aqueous buffer or incubated for 24 h to produce conditioned media (CM). The recovered material was then analysed for IL-1 bioactivity in a sensitive murine thymocyte proliferation assay. When divided into four stage groups, extracts of stages II-VI, IX-XII and XIII-I showed equally high IL-1 activity whereas stage group VII-VIII showed much lower activity. More detailed analysis with 10 different stage groups showed that tIL-1 activity was undetectable in extracts of substages VIIab and VIIcd. The same pattern was seen when CM from cultured tubular segments were analysed. Labelling of seminiferous tubules with tritiated thymidine in vitro and analysis by autoradiography revealed that DNA-synthesizing spermatogonia were absent in substages VIIb and VIIc and sparse in substages VIIa and VIId. The results show that tIL-1 activity is produced in a stage-dependent manner and suggest that tIL-1 might be involved in the regulation of spermatogonial proliferation in vivo.

Animals↗
PubMed1991

Combination of a GnRH agonist with an antiandrogen or bromocriptine in the treatment of prostatic cancer; slight potentiation of antigonadal effects.

The effect of combined treatment with a GnRH agonist (buserelin depot, BUS, 6.6 mg every 2 months) with an antiandrogen (cyproterone acetate, CPA, 300 mg day-1) or a prolactin-suppressing agent (bromocriptine, BR, 20 mg day-1) on pituitary-testicular function were studied in patients with advanced prostatic carcinoma. The patients (n = 5-6 per group) were treated in this fashion for 6 months and thereafter orchidectomized. Serum testosterone and gonadotrophin responses were followed during treatment, and histology and certain endocrine parameters were studied using testicular tissue obtained at orchidectomy. Serum LH was suppressed in all treatment groups from mean levels of 4-6 IU l-1 to less than 0.1 IU l-1, whilst serum FSH levels decreased in all groups during the first month of therapy from 4.5-7 to 1-2 IU l-1, but recovered thereafter. Only minor increases in serum gonadotrophin levels were evident 3 months after castration. No differences in gonadotrophin responses were seen between the different treatment groups. Serum levels of testosterone were suppressed from 15-20 nmol l-1 to the castrate range (approximately 1 nmol l-1), in each of the treatment groups. Testicular weight decreased significantly more (P less than 0.05) in the BUS + CPA group, compared to the other treatments. No differences were found in the testicular concentration of testosterone, or LH and FSH receptors between the three treatment groups. On histological examination, spermatogenesis was found to be impaired severely in all groups, with the lowest Johnsen score in the BUS + BR group (2.16 +/- 0.13, vs. 2.73 +/- 0.25 with BUS alone, P less than 0.05). Seminiferous tubular diameters were reduced similarly in all treatment groups. In conclusion, the combination of CPA or BR with BUS in the treatment of prostatic carcinoma does not potentiate the suppression of gonadotrophin or testosterone secretion, evidently because the GnRH agonist exerts a maximal suppressing effect. However, other antigonadal effects were enhanced slightly, including suppressed testicular weights by CPA and further suppression of spermatogenesis by BR.

Adult↗
PubMed1991

In vitro stimulation of stage-specific deoxyribonucleic acid synthesis in rat seminiferous tubule segments by interleukin-1 alpha.

Levels of rat testicular interleukin-1-like factor (tIL-1) have been shown to correlate with DNA synthetic activity during the cycle of the rat seminiferous epithelium, suggesting its role as a spermatogonial or meiotic growth factor. To explore this further, a new in vitro model system was developed. Rat seminiferous tubule segments from stages I, V, VIIa, and VIII-IX of the cycle were isolated by transillumination-assisted microdissection, cultured in chemically defined serum-free medium supplemented with human recombinant IL-1 alpha, and labeled with [3H]thymidine. During incubation, spontaneous progression of spermatogenesis was noted. Inactive stage VIIa tubule segments differentiated to stage VIII and initiated DNA synthesis, and concomitantly started to secrete IL-1-like factor. DNA synthesis of stages VIII-IX ceased through differentiation of spermatocytes to leptotene-zygotene (stages XII-XIII of the cycle). IL-1 alpha stimulated DNA synthesis significantly in spermatogonia of stage I. Meiotic DNA synthesis at stage VIIa was stimulated (48 h/34 C) and maintained at stages VIII-IX (48 h/34 C). IL-1 alpha seems to act as a regulator of spermatogenic DNA synthesis in both mitotic and meiotic phases. It has mainly stimulating and maintaining effects, but it may also be inhibitory under certain conditions.

Animals↗
PubMed1990

Stage- and cell-specific expression of the ornithine decarboxylase gene during rat and mouse spermatogenesis.

Ornithine decarboxylase (ODC) is an enzyme that has been shown to be induced in the growth, differentiation and proliferation of cells. We have used a cDNA probe to determine ODC mRNA levels in different stages of the cycle of rat and mouse seminiferous epithelium. For Northern and slot-blot hybridizations, RNA was isolated from microdissected staged seminiferous tubules. Cell-specific localization of ODC mRNA was studied by in situ hybridization. In the rat, in situ hybridization showed increasing mRNA levels during prophase of meiosis with the highest mRNA levels seen in late pachytene spermatocytes and step 3-5 spermatids. In the mouse, the mRNA levels increased in a similar fashion and the highest mRNA levels were found in step 1-8 spermatids. In the rat, Northern blot hybridizations revealed three molecular sizes of ODC mRNA: 2.2, 2.7 and 1.6 kb. The levels of all molecular sizes were highest in stages VII-VIII, and the lowest mRNA levels were seen in stage I of the seminiferous epithelial cycle. The level of the 2.2 kb transcript was low during stages XIII-I. In the mouse, the Northern blot hybridizations also showed three molecular sizes of ODC mRNA: 2.2 and 2.7 kb and very low levels of 1.6 kb transcript. The levels of the transcripts were steady throughout the cycle. In the mouse, the 2.2 kb transcript was more abundant than the 2.7 kb transcript indicating a species difference between rat and mouse in the usage of the two polyadenylation signals within the ODC gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Testosterone micromilieu in staged rat seminiferous tubules.

Endogenous testosterone concentrations in rat seminiferous tubules were measured in relation to different stages of the cycle of the seminiferous epithelium. For this purpose, the seminiferous tubules were mechanically separated from the interstitial tissue on a cooled (1 degree C) petri dish under a stereomicroscope without added medium. After recognition of the stages of the cycle by transillumination, the specimens were rapidly transferred by dry forceps into test tubes for testosterone radioimmunoassay. The results of the dry dissection method were compared with measurements on tubules that were kept after separation in phosphate buffered saline (PBS, pH 7.4), in order to reveal the possible leakage of testosterone from the tubules. The maximal concentration of testosterone per unit length of seminiferous tubule was found in stages VII and VIII of the cycle (288 +/- 60 fmol/cm, mean +/- SEM, n = 12), and the minimal in stages IX-XII (219 +/- 57 fmol/cm, P less than 0.01). If the levels were correlated with unit volumes of the seminiferous tubules, identical concentrations of testosterone (521-542 fmol/mm3, approx. 500 nmol/l) were found in the different stages of the cycle. Despite the similarity of testosterone concentrations in the different parts of the seminiferous tubules the local concentrations of biologically active (i.e. free) testosterone may be modulated by extracellular and intracellular androgen binding components.

Animals↗
PubMed1990

Cellular regulation of basal and FSH-stimulated cyclic AMP production in irradiated rat testes.

Basal and follicle-stimulating hormone (FSH)-stimulated cyclic AMP (cAMP) productions by seminiferous tubular segments from irradiated adult rats were investigated at defined stages of the epithelial cycle when specific spermatogenic cells were low in number. Seven days post-irradiation, depletion of spermatogonia did not influence the basal cAMP production, but FSH response increased in stages II-VIII. Seventeen days post-irradiation when spermatocytes were low in number, there was a small increase in basal cAMP level in stages VII-VIII and FSH-stimulated cAMP production increased in stages VII-XII and XIII-I. At 38 days when pachytene spermatocytes and round spermatids (steps 1-6) were low in number, a decreased basal cAMP production was measured in stages II-VI and IX-XII. FSH-stimulated cAMP output increased in stages VII-XII but decreased in stages II-VI. At 52 days when all spermatids were low in number, basal cAMP levels decreased in all stages of the cycle, whereas FSH response was elevated only in stages VII-XII. All spermatogenic cell types seem to have an effect on cAMP production by the seminiferous tubule in a stage-specific fashion. Germ cells appear to regulate Sertoli cell FSH response in a paracrine way, and a part of cAMP may originate from spermatids stimulated by an unknown FSH-dependent Sertoli cell factor. The FSH-dependent functions may control such phenomena as spermatogonial proliferation, final maturation of spermatids, and onset of meiosis.

Animals↗
PubMed1990

Modulation of basal and FSH-dependent cyclic AMP production in rat seminiferous tubules staged by an improved transillumination technique.

The stage-dependent action of follicle-stimulating hormone (FSH) in the rat seminiferous epithelium was investigated in microdissected 1 mm tubule segments, where the precise stage of the cycle was identified by a rapid screening method of live cell squash preparations. For distinction of stages I and II and the substages of VII, new criteria were used. The step 16 spermatids with rapid assembly of outer dense fibers leading to marked increase of flagellar thickness were used for distinction of stages I and II. The form and density of the cytoplasmic lobes of step 19 spermatids was used for recognition of substages of VII. Highest basal production of cyclic AMP (cAMP, measured by radioimmunoassay) was found in stage II of the cycle and stages XIV-I-VI had higher values than did stages VII-XIII. A decline occurred during stage VII and an increase at stage XIV. When stimulated with FSH, highest cAMP secretion was found in stage IV of the cycle; again, stages XIV-I-VI had higher values than did other stages. A small but significant (P less than .01) stimulation was found at substage VIId. FSH-stimulated and basal cAMP productions of different stages were compared, highest values were found at stages IV and XIII, and lowest, at stages VIIa-c and IX of the cycle. Since the FSH-dependent cAMP production is confined to Sertoli cells, and the number of these cells is constant per unit length of seminiferous tubules, the Sertoli cells are obviously under a stage-specific paracrine control by the surrounding spermatogenic cells. Specific steps in cell differentiation, such as spermatogonial proliferation, final maturation of the spermatids (stages I-VII), onset of meiosis (substage VIId), and completion of meiotic divisions (stage XIV) may be involved in this interaction.

Animals↗
PubMed1990

Inhibition of meiotic divisions of rat spermatocytes in vitro by polycyclic aromatic hydrocarbons.

The toxic effects of polycyclic aromatic hydrocarbons (PAH) on spermatogenic cells undergoing meiotic division were investigated in vitro. Toxicity was assayed as alterations in cell nucleus morphology and cell survival and by DNA flow cytometry. Benzo[a]pyrene (BP) and 7,12-dimethylbenz[a]anthracene (DMBA) inhibited the progression of spermatocytes through meiotic division and were highly cytotoxic at concentrations higher than 1 microM. These results were obtained upon addition of a drug-metabolizing system, indicating that the seminiferous tubules lack the enzymes required for the initiation of PAH metabolism. The spindle poisons, e.g., vincristine and Colcemid, a group of direct-acting agents, affected spermatogenesis during meiotic division in a manner similar to that observed with PAH. In contrast, adriamycin did not inhibit meiotic division, although it did induce the formation of meiotic micronuclei as a result of chromosome breakage. It is concluded that low concentrations, i.e., 0.1 microM of PAH, strongly inhibit meiotic division, presumably after metabolic activation to reactive molecules functionally resembling direct-acting alkylating agents. High concentrations of PAH are cytotoxic.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1990

Regulation of the testis.

The testicular cells are regulated by factors produced locally in the testis. These factors include peptide growth factors, pro-opiomelanocortin derivatives, neuropeptides and steroids. Several agents able to affect steroido- and spermatogenesis can also affect leukocytes and many of the testis-regulating factors are produced by immune cells, suggesting that testicular cells and leukocytes may interact. In the present article, the effects of various testicular cell and leukocyte produced factors on steroido- and spermatogenesis are reviewed. The possibility that leukocytes may produce substances able to affect the testicular functions suggests that inhibition of immune system activation in the testis may be important also for reasons other than protection of autoantigenic germ cells from an autoimmune attack.

Androgens↗
PubMed1989

Inhibition of stage-specific DNA synthesis in rat spermatogenic cells by polycyclic aromatic hydrocarbons.

Changes in the rate of DNA synthesis in spermatogenic cells after treatment of segments of rat seminiferous tubule at defined stages of epithelial cycle with benzo[a]pyrene (BP) or 7,12-methylbenz[a]anthracene (DMBA) were studied. The incorporation of labeled thymidine into DNA was used as a measure of the rate of DNA synthesis. Very little or no inhibition of DNA synthesis at stages V and VIII of the cycle was observed at BP and DMBA concentrations lower than 100 microM. In contrast, in the presence of added mitochondria and/or microsomes from whole rat testis, 20 microM BP or DMBA inhibited DNA synthesis 5% and 80%, respectively. This inhibition of DNA synthesis was prevented by inhibitors of the cytochrome P-450 system and by free radical scavengers. These results suggest that polycyclic aromatic hydrocarbons (PAH) require metabolic activation in order to inhibit DNA replication in seminiferous tubules. The first step of this biotransformation is cytochrome P-450-dependent and occurs in Leydig cells. However, the metabolites produced in this step may be further metabolized to reactive metabolites by peroxidative pathways in the seminiferous tubules; these latter products may affect DNA replication.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Pertussis toxin enhances follicle-stimulating hormone-stimulated cAMP production in rat seminiferous tubules in a stage-dependent manner.

Cyclic (c) AMP production was measured in vitro in dissected pieces of adult rat seminiferous tubules of defined stages of the seminiferous epithelial cycle (VII-VIII and XIV-IV) in the absence and presence of human follicle-stimulating hormone (FSH) (Metrodin, Serono). The basal rate of cAMP production was stage dependent, being about 2-fold higher in stages XIV-IV. FSH stimulated cAMP output in a time- and dose-dependent (stimulation at doses greater than or equal to 3 mg/l) fashion, and also the stimulability of stages XIV-IV (on average 2-fold) was greater than that of stages VII-VIII. When the tubular pieces were incubated in the presence of pertussis toxin (PT, 100 micrograms/l), the FSH-stimulated cAMP production of stages VII-VIII was enhanced by about 2-fold (P less than 0.01) whereas the basal rate was unaffected. In contrast, neither the basal nor the FSH-stimulated cAMP production of stages XIV-IV were affected by PT. Presence of the Gi-protein in both stages studied was demonstrated with PT-induced ADP ribosylation. However, no release of a putative activator of the Gi-protein could be demonstrated into spent media of the seminiferous tubules when incubated with freshly separated tubules. It is concluded that the poor FSH stimulability in cAMP production of certain spermatogenic stages of adult seminiferous tubules is at least partly due to endogenous inhibitors acting through the inhibitory Gi-protein. This inhibition could be demonstrated in a stage-dependent manner, and was present in stages with the lowest production and least stimulability of cAMP production by FSH.

Animals↗