Biomedical subjects

D M de Kretser

Publications and source records attributed to D M de Kretser.

At least 163 records · Page 9Linked to original sources

PubMed1990

Quantitative cytological studies of spermatogenesis in intact and hypophysectomized rats: identification of androgen-dependent stages.

A stereological study of the numbers of germ cells in various stages of spermatogenesis was undertaken in testosterone-treated intact and hypophysectomized (HPX) rats. Adult Sprague-Dawley rats were given testosterone by Silastic implants, which either inhibited (3-cm length) or partially maintained (10 cm) spermatogenesis over a 13-week period. The numbers of nuclei of the various germ cell categories (spermatogonia, spermatocytes, and round spermatids) in the testes were estimated by profile counting and measurement of nuclear diameter. The numbers of elongated spermatids were determined separately in testicular homogenates. Testis weight, seminiferous tubule volume, and tubule diameter were significantly decreased in intact rats with 3- and 10-cm testosterone implants and in HPX rats, although they were partially maintained in groups with 10-cm implants compared to those in groups with 3-cm implants (P less than 0.05). The effect of 3-cm testosterone implants in the intact group was to suppress the number of spermatogonia to 57%, reduce the conversion of spermatogonia to spermatocytes to 85%, and reduce the conversion of round to elongated spermatids to 19% of the control value. This latter effect was largely overcome with 10-cm testosterone implants. In HPX rats, only 10-cm implants were effective in maintaining the conversion of round spermatids to elongated spermatids. However, testosterone alone was less effective in maintaining the conversion of spermatocytes to round spermatids, suggesting that a pituitary factor, probably FSH, was involved. It is concluded that testosterone has a major effect on the conversion of round to elongated spermatids. The conversion of spermatogonia to spermatocytes and the conversion of spermatocytes to round spermatids depend on the synergistic action of both FSH and testosterone. However, the effect of FSH is greatest on the conversion of spermatocytes to spermatids, i.e. meiosis.

Animals↗

PubMed1990

The quantification of steroidogenesis-stimulating activity in testicular interstitial fluid by an in vitro bioassay employing adult rat Leydig cells.

An in vitro bioassay for steroidogenesis-stimulating activity (SSA) in charcoal-extracted rat testicular interstitial fluid (IF) was developed. The bioassay was based upon stimulation of testosterone production by Percoll gradient-purified adult rat Leydig cells during a 20 h incubation in the presence of a maximally stimulating dose of human CG (hCG). The hCG-stimulated conditions were employed to avoid assay interference by endogenous LH in the sample preparations. The standard preparation (a pool of IF from normal adult rats) stimulated testosterone production 3- to 4-fold above that obtained with a maximal dose of either hCG or LH alone, and a linear log dose-testosterone response was observed over the range from 150% to 300% of hCG-stimulated testosterone production. The bioassay had a mean index of precision (lambda) of 0.13 (n = 10 assays), a between assay variation of 10.7-11.7%, and a useful working range from 4.9-28 microliters IF including at least three serial half-dilutions. Parallelism with the IF standard was obtained with IF collected from aged (greater than 15 months old) rats, adult rats made bilaterally cryptorchid for either 4 weeks or 12 months, or injected 6 h previously with 100 IU hCG, and with ovine testicular lymph. Testicular SSA was not affected by coincubation with rat LH antiserum and was not attributable to prevention of oxygen-mediated enzyme damage during the incubation period. Although charcoal-extracted rat serum log dose-response relationships were nonparallel with the standard, serum displayed an apparent relative bioactivity of approximately 20% that of normal IF based on ED50 comparisons. The activity of testicular IF was not affected by coincubation with serum. Untreated and charcoal-extracted rat albumin, at an assay concentration equivalent to that present in normal rat serum or IF, caused only a minor stimulation of testosterone production. Charcoal-extracted bovine albumin, ovalbumin, epidermal growth factor, insulin-like growth factor-1, bovine 31 kDa inhibin, and transforming growth factor-beta were inactive. Activity was nondetectable in rat thoracic duct lymph or high speed supernatants of adult rat testicular extracts. Testicular SSA and serum from normal rats displayed slightly different time-courses of action, with SSA active during both acute (1.0 h) and longer term (2.0-20 h) incubations, while serum stimulated testosterone production only in the longer term incubations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

In vitro bioactive and immunoactive inhibin concentrations in bovine fetal ovaries and testes throughout gestation.

This study investigates the concentrations of inhibin in the bovine fetal ovary and testis throughout gestation (days 40 to 270/term) as determined by inhibin in vitro bioassay and RIA techniques. In addition, the expression of the inhibin alpha- and beta-subunits (beta A and beta B) in these tissues was evaluated by Northern blot analysis and in situ hybridization. Testicular concentrations of inhibin bioactivity and immunoactivity increased 2.5-fold (103 +/- 24.5 to 256 +/- 11.7 U/g wet weight; mean +/- SE) and 10.4-fold (139 +/- 56 to 1430 +/- 172) respectively, between 90 days and term. The corresponding ratio of inhibin biological: immunological activities (B/I ratio) decreased 8.3-fold (1.5 +/- 0.7 to 0.18 +/- 0.01). The concentration of ovarian bioactive inhibin increased significantly (P less than 0.05) 4.6-fold between 90 days and term (73.6 +/- 14.7 to 340 +/- 11.1 U/g wet weight), whereas the immunoactive inhibin concentration increased 10.3-fold between 120 and 210 days of gestation (7.2 +/- 1.9 to 40.0 +/- 8.7). The corresponding B/I ratio remained unchanged throughout gestation (8.3 +/- 2.4 to 12.5 +/- 4.0). Although the levels of alpha subunit mRNA in the testis and ovary increased over gestation, the levels of testicular beta A subunit mRNA remained low and unchanged. Ovarian levels of beta A subunit mRNA were also low but variable. Furthermore, no beta B subunit mRNA could be detected in gonadal tissue throughout gestation. alpha-Subunit mRNA was detected by in situ hybridization in the sex cords of the fetal testis and the granulosa cells of the fetal ovary while beta A subunit mRNA was detected only in the granulosa cells of the fetal ovary. It is concluded that inhibin is produced by the fetal testis and ovary and these tissue levels increase throughout gestation. The location of alpha- and beta A-subunit mRNA to the sex cords of the testis and granulosa cells of the ovary indicate that these cells are the primary source of inhibin production. The rapid fall in inhibin B/I ratio in testicular extracts over gestation is attributed to the production of an inhibin-related protein with limited or negligible biological activity.

Animals↗

PubMed1990

Inhibin and estradiol responses to ovarian hyperstimulation: effects of age and predictive value for in vitro fertilization outcome.

We have compared the time courses of serum inhibin and estradiol responses to ovarian hyperstimulation in patients undergoing in vitro fertilization and embryo transfer as well as their predictive value for outcome of intermediate variables and pregnancy in in vitro fertilization and embryo transfer. Blood samples (n = 749) were collected for up to 6 days before hCG administration in 100 consecutive treatment cycles, of which 44 resulted in pregnancy, as defined by elevated luteal phase serum hCG beta levels. Inhibin and estradiol levels increased markedly in parallel during hyperstimulation and were highly correlated (r = 0.89; P less than 0.001). Inhibin responses were significantly lower in women 35 yr of age or older (P less than 0.001), although estradiol responses were not influenced by age. Gravidity and tubal disease also had marginal effects on the time course of inhibin responses, but not on overall mean inhibin levels or estradiol responses. The time course of hormonal responses to hyperstimulation was not influenced by any other demographic or etiological factors. Peak values of both hormones correlated with the total number of follicles (inhibin, r = 0.70; estradiol, r = 0.65; P less than 0.001) and oocytes retrieved per cycle (inhibin, r = 0.49; estradiol, r = 0.39; P less than 0.001). The time course and peak values of inhibin and estradiol responses to hyperstimulation did not differ significantly between conception or nonconception cycles whether judged by biochemical (luteal hCG beta) or clinical (viable ongoing pregnancy) criteria. Luteal phase serum inhibin, estradiol, progesterone, and hCG levels were significantly higher in conception than in nonconception cycles (P less than 0.001). These data suggest that the rises in serum inhibin and estradiol levels during hyperstimulation have similar predictive properties for IVF-ET outcomes and could, therefore, be used interchangeably to monitor hyperstimulation regimens. The age-related reduction in inhibin, but not estradiol, responses suggests that these two hormones reflect different granulosa cell functions and that serum inhibin responses to maximal ovarian stimulation may be a sensitive and early index of declining ovarian function with advancing age.

Adult↗

PubMed1990

Current perspectives of inhibin biology.

Inhibin is generally considered to be a feedback regulator of FSH secretion, but significant progress in the field of inhibin biology over the past four years has widened our perspective of inhibin and its production, regulation and action. Firstly, inhibin is a member of a larger family of hormones, secondly it is produced by organs other than the gonads, and thirdly its action is not confined to the pituitary gland. In this review we will outline the isolation and characterization of inhibin related peptides and their production by the Sertoli and granulosa cells of the testis and ovary. With this information in mind, more recent studies concerning the measurement, production, regulation and action of inhibin and inhibin-related proteins will be discussed, in an effort to alert the reader to the contemporary and controversial issues concerning inhibin biology.

Animals↗

PubMed1990

Effects of bovine 35 kDa FSH-suppressing protein on FSH and LH in rat pituitary cells in vitro: comparison with bovine 31 kDa inhibin.

The mode of action of a recently isolated gonadal protein, termed FSH-suppressing protein (FSP) or follistatin, on basal and gonadotrophin-releasing hormone (GnRH)-stimulated release of FSH and LH and on pituitary cell content of FSH and LH was examined in rat pituitary cell cultures and compared with the previously reported effects of inhibin. Pituitary cells were cultured for 3-9 days in the presence of graded doses of FSP and the basal release rates and changes in cell contents of FSH and LH determined during this period. FSP suppressed both the basal release rate and the cell content of FSH with median inhibitory concentrations (IC50) of 135 and 161 pmol/l respectively. The corresponding effects of FSP on LH basal release rate and LH cell content (IC50 = 200 pmol/l) were limited compared with the effects on FSH. The effect of FSP on GnRH-stimulated release of FSH and LH during 4 h was determined in cells which had been preincubated with FSP for 3 days, and the GnRH-stimulated release of FSH and LH analysed as a percentage of the respective gonadotrophin available for release. FSP antagonized GnRH action with dose-related increases in the GnRH median effective (stimulatory) concentrations for FSH and LH release (EC50 values = 56 and 400 pmol/l respectively) and a suppression in the maximum release of FSH and LH by excess GnRH (IC50 values = 142 and 150 pmol/l respectively). The effect of FSP on FSH cell content after 3 days in culture was insensitive to the neutralizing effects of an inhibin antiserum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Inhibin: a new circulating marker of hydatidiform mole?

OBJECTIVE: To define the concentrations of inhibin in serum and tissue of patients with hydatidiform mole and assess their value as a clinical marker of the condition. DESIGN: Prospective study of new patients with hydatidiform mole, comparison of paired observations, and case-control analysis. SETTING: A university hospital, two large public hospitals, and a private women's clinic in Japan. PATIENTS: Seven consecutive referred patients seen over four months with newly diagnosed complete hydatidiform mole, including one in whom the mole was accompanied by viable twin fetuses (case excluded from statistical analysis because of unique clinical features). All patients followed up for six months after evacuation of molar tissue. END POINT: Correlation of serum inhibin concentrations with trophoblastic disease. MEASUREMENTS AND MAIN RESULTS: Serum concentrations of inhibin, human chorionic gonadotrophin, and follicle stimulating hormone were compared before and seven to 10 days after evacuation of the mole. Before evacuation the serum inhibin concentrations (median 8.3 U/ml; 95% confidence interval 2.4 to 34.5) were significantly greater than in 21 normal women at the same stage of pregnancy (2.8 U/ml; 2.1 to 3.6), and inhibin in molar tissue was also present in high concentrations (578 U/ml cytosol; 158 to 1162). Seven to 10 days after evacuation inhibin concentrations in serum samples from the same patients declined significantly to values (0.4 U/ml; 0.1 to 1.4) similar to those seen in the follicular phase of normal menstrual cycles. None of the four patients whose serum inhibin concentrations were 0.4 U/ml or less after evacuation developed persistent trophoblastic disease. Though serum human chorionic gonadotrophin concentrations declined after evacuation (6.6 x 10(3) IU/l; 0.8 x 10(3) to 32.6 x 10(3], they remained far higher than in non-pregnant women. Serum follicle stimulating hormone concentrations remained suppressed. CONCLUSIONS: In this small study serum inhibin concentrations higher than those found in the early follicular phase one to two weeks after evacuation of a hydatidiform mole seemed to be specific for persistent trophoblastic disease. Further data are needed to confirm these promising results.

Adolescent↗

PubMed1989

Inhibin as an oocyte meiotic inhibitor.

The effect of inhibin on oocyte maturation division was studied in vitro. Inhibin inhibited spontaneous division in both cumulus enclosed and denuded rate oocytes obtained from immature rats. The inhibition was dose-dependent (15-5000 units/ml) with an ED50 of 45.8 units/ml (4.00 nM). Follicle stimulating hormone (FSH) suppressing protein (FSP) which has inhibin-like activity accelerated the rate of meiotic maturation of rat oocytes in culture (P less than 0.05, at a dose of 0.7 microgram/ml) while activin, which has opposite biological effects to inhibin in many systems did not significantly stimulate oocyte maturation at a dose of 1.12 micrograms/ml. The actions of the three proteins studied were reversible.

Activins↗

PubMed1989

Immuno- and bioactive inhibin and inhibin alpha-subunit expression in rat Leydig cell cultures.

The rise in serum immunoactive inhibin levels in male rats following hCG stimulation raised the possibility that Leydig cells may produce inhibin. This study therefore evaluated whether Percoll-purified Leydig cells from adult male rats synthesized and secreted inhibin in vitro as measured by Northern blot analysis, radioimmunoassay and in vitro bioassay. Northern blot analysis demonstrated the presence of alpha-inhibin subunit mRNA in the Leydig cell and inhibin bioactivity was detected in Leydig cell culture media. Levels of immunoactive inhibin increased in culture over 20 h and were directly dependent on the number of Leydig cells in culture. rLH (NIADDK-rLH-I-6) and not rFSH (NIADDK-rFSH-I-6) stimulated immunoactive inhibin levels in a dose-dependent manner. This study demonstrates that Leydig cells express mRNA for the alpha-subunit of inhibin and produce inhibin which is biologically and immunologically active prompting a re-evaluation of our concepts of testicular inhibin production.

Animals↗

PubMed1989

The effect of insulin on inhibin production in isolated seminiferous tubule segments from adult rats cultured in vitro.

The effect of insulin and its interaction with intracellular messenger systems on in vitro inhibin production by adult rat isolated seminiferous tubules has been investigated using a recently developed inhibin radioimmunoassay (RIA). Seminiferous tubule segments (5 cm) from intact adult rats were exposed to insulin (0.05-5000 ng/ml) for 2 days of culture. Insulin caused a dose-dependent inhibition of basal inhibin secretion with reversal of this inhibition at very high doses (5000 ng/ml). The ability of follicle-stimulating hormone (FSH) to induce inhibin secretion was also inhibited by insulin (50 ng/ml). Insulin reduced the stimulation of inhibin production by dibutyryl cyclic AMP (dbcAMP) and this effect was prevented by the addition of theophylline (0.4 mM), while theophylline alone was unable to prevent the effect of insulin on basal inhibin secretion. Phorbol 12-myristate 13-acetate (PMA) mimicked the effect of insulin reducing basal and FSH-induced secretion of inhibin. No additive effects on basal inhibin secretion were observed with a combination of PMA and insulin. Ethylenediaminetetraacetic acid (EDTA, 2 mM) significantly reduced basal and FSH-induced inhibin production, while the combined effects of EDTA and insulin on basal and FSH-induced inhibin production were additive. These data demonstrate an inhibitory effect of insulin on inhibin production by isolated seminiferous tubules mediated via at least two mechanisms namely the inhibition of the cAMP-protein kinase A system and stimulation of protein kinase C activity.

Animals↗

PubMed1989

Inhibin and activin regulate [3H]thymidine uptake by rat thymocytes and 3T3 cells in vitro.

[3H]Thymidine incorporation by adult rat thymocytes, in the presence of phytohaemagglutinin (PHA), was stimulated by bovine inhibin (ED50 0.7 nM), and inhibited by bovine activin (ID50 0.4 nM) and porcine transforming growth factor-beta (TGF-beta) (ID50 4 pM); inhibin opposed the actions of activin and TGF-beta. Bovine 35 kDa follicle stimulating hormone (FSH) suppressing protein (FSP) had no effect on either unstimulated or PHA-stimulated thymocytes. Inhibin also stimulated thymocytes in the presence of a submaximal dose of concanavalin A (ConA), and in the absence of either lectin. Thymocytes which had been maximally stimulated by ConA were inhibited by TGF-beta (ID50 0.02 nM), but not affected by inhibin and activin. Both activin and TGF-beta stimulated [3H]thymidine uptake by 3T3 fibroblasts, but inhibin and FSP had no effect, alone or on activin-stimulated 3T3 fibroblasts. The results indicate that inhibin and activin have opposing, cell type-specific effects on the proliferation of T-lymphocytes, while activin also stimulates fibroblast proliferation in vitro.

Animals↗

PubMed1989

Follitropin (FSH) stimulation of inhibin biological and immunological activities by seminiferous tubules and Sertoli cell cultures from immature rats.

Seminiferous tubules from 20-day-old rats were isolated by mechanical dissection and the conditions to produce optimal inhibin secretion over a 5-day period of culture were established. Inhibin was measured by a specific heterologous radioimmunoassay and by an in vitro bioassay using rat pituitary cells in culture. The tubule production of biologically and immunologically active inhibin was stimulated by ovine follitropin (FSH); however, the ratio of biological to immunological (B:I) activity fell significantly with increasing dose. A similar stimulation of both B and I inhibin activity with a corresponding decrease in B:I ratio with increased FSH dose was also observed using isolated immature Sertoli cells in culture. Fractionation of seminiferous tubule and Sertoli cell culture media by reverse-phase high-performance liquid chromatography (HPLC) revealed the presence of two peaks (I and II) with inhibin biological and immunological activity both of which increased following FSH stimulation. However, while the B:I ratio for peak I remained unchanged following FSH stimulation, the B:I ratio for peak II significantly fell. The molecular weights of peak I and II immunoactivity, determined following fractionation on preparative polyacrylamide gel electrophoresis were 30 kDa and 27 kDa respectively. The 30 kDa peak, based on its inhibin in vitro biological and immunological activity, molecular weight and retention position on HPLC most likely represent 30-32 kDa inhibin. The 27 kDa material remains to be identified.

Animals↗

PubMed1989

Stage-specific inhibin secretion by rat seminiferous tubules.

The endogenous inhibin content was measured by radioimmunoassay in segments of seminiferous tubules at specific stages of the spermatogenic cycle isolated by transillumination-assisted dissection as described by Parvinen (1982). In addition, the immunoactive inhibin production in response to FSH stimulation was investigated. The inhibin content was greatest in tubules at stages II-VI of the cycle and was lowest at stages VII-VIII. Over 48 h of culture, the secretion of inhibin into the medium was greatest at stages XIII-VI and lowest at stages VII-VIII. The inhibin response to FSH stimulation was greatest at stages IX-XIII and least at stages VII-VIII. The results demonstrate that the secretion of inhibin by adult tubules in vitro varies according to the stage of the seminiferous cycle.

Animals↗

PubMed1989

The isolation and physiology of inhibin and related proteins.

Inhibin, a glycoprotein that preferentially suppresses follicle-stimulating hormone (FSH) secretion, has been isolated from follicular fluid as a heterodimer of two dissimilar subunits linked by disulphide bonds. The larger subunit is termed alpha and the smaller is designated beta. Two forms of inhibin termed A and B have been isolated, the differences being due to variations in the amino acid sequence of the beta-subunit; Inhibin A consists of alpha-beta and Inhibin B of alpha-beta B. Dimers of the beta-subunit, termed activins, have also been found in follicular fluid; these stimulate pituitary FSH secretion. Inhibin is produced in the female by the granulosa cell and corpus luteum under the control of FSH and luteinizing hormone (LH), respectively. The levels in serum rise to peak at mid-cycle and in the mid-luteal phase of the human menstrual cycle, and decline prior to menstruation. In pregnancy, the late-luteal phase decline in inhibin does not occur and the levels increase slowly. Studies suggest that the levels in pregnancy arise from an embryonic source, particularly the placenta. In the male, inhibin is produced by the Sertoli cells under the control of FSH by mechanisms involving cyclic adenosine 3', 5'-monophosphate. Testosterone exerts a minor inhibitory control at supraphysiological levels (10(-5) M), but human chorionic gonadotropin stimulation results paradoxically in a rise in serum inhibin levels. Disruption of spermatogenesis in the rat by cryptorchidism, heat treatment, or efferent duct ligation results in a decline in inhibin levels and a rise in FSH levels, findings consistent with the negative feedback action of inhibin on FSH secretion. As well as their roles in the reproductive system, inhibin and activin have more widespread actions in the haemopoietic, immune and nervous systems as evidenced by the finding of mRNA for its subunits in a range of tissues. Other studies have shown actions on erythroid differentiation and on mitotic activity in thymocytes. These actions suggest that inhibin and activin may function as growth factors as well as regulators of FSH.

Animals↗

PubMed1989

The involvement of Leydig cells in the regulation of inhibin secretion by the testis.

The stimulation of Leydig cells by the administration of a single injection of 100 IU human CG (hCG) to adult male rats caused a significant biphasic stimulation of serum testosterone levels at 2 h and 3 days after injection. Serum immunoreactive (IR)-inhibin levels were elevated by 6 h and peaked at 24 h after hCG, then progressively declined thereafter. The removal of Leydig cells in vivo by the injection of the cytotoxic drug ethane dimethane sulfonate (EDS) causes a significant decrease in serum testosterone levels within 4 days, which is sustained 1 and 2 weeks after EDS. Serum IR-inhibin levels, however, rise significantly 2 and 4 weeks after injection of EDS. An injection of 100 IU hCG, 4 days after EDS (when no Leydig cells were present in vivo), failed to provoke an elevation of either testosterone or IR-inhibin levels in serum. But 2 or 4 weeks after administration of EDS, as a new population of Leydig cells develops in the interstitium, an injection of 100 IU hCG provokes a significant increase in serum testosterone and IR-inhibin levels. The possibility that the failure of IR-inhibin levels to rise after EDS and hCG treatment could be due to changes in the seminiferous epithelium, caused by testosterone deprivation induced by Leydig cell destruction after EDS, was examined by administering high doses of testosterone known to maintain spermatogenesis. Under such conditions, hCG failed to induce a rise of IR-inhibin after EDS treatment had destroyed the Leydig cells. These data strongly support the concept that the Leydig cells are involved in the regulation of IR-inhibin secretion in vivo through factors other than testosterone.

Animals↗

PubMed1989

The effects of exogenously administered testosterone on spermatogenesis in intact and hypophysectomized rats.

The effects of exogenously administered testosterone on the maintenance of spermatogenesis in intact and hypophysectomized rats were examined. Adult male rats were given Silastic implants containing testosterone in lengths ranging from 0.5-20 cm, and their effects on daily sperm production (DSP); serum FSH, LH, and testosterone; and interstitial fluid testosterone were determined in intact and hypophysectomized rats over a 13-week period. In intact rats, DSP levels were suppressed to 4-30% of control values at lower testosterone doses (2- to 6-cm implants), while DSP levels were partially maintained (65-93%) at higher doses (greater than or equal to 8 cm implants). Under these conditions LH levels were suppressed while FSH levels were reduced to 30-60% of control values. A steep testosterone-induced change in DSP levels was observed in both intact (2- to 3-fold) and hypophysectomized (18-fold) animals over a narrow testosterone dose range (implant lengths, 6-8 cm). Interstitial fluid testosterone levels associated with this change in DSP levels range from 6-8% of control values, while serum testosterone levels were elevated 1- to 2-fold above control values. A comparison of the testosterone implant lengths that caused a 50% change in DSP levels after 7 weeks of treatment was similar in intact and hypophysectomized rats. At high testosterone doses (greater than or equal to 10-cm implants), maximal DSP levels decreased 10% by 7 weeks and 35% by 13 weeks. DSP and serum testosterone levels were highly correlated (r = 0.54-0.83), while DSP and interstitial fluid testosterone showed a less correlation (r = 0.36-0.70) under the various experimental conditions examined. In conclusion, the testosterone-induced maintenance of DSP in rats is associated with several dose-related responses or events that appear to be differentially regulated. At low testosterone concentrations, DSP levels are partially maintained in intact rats but are totally suppressed in hypophysectomised rats, suggesting that a pituitary factor, probably FSH, has a potentiating effect at these testosterone concentrations. At intermediate testosterone doses resulting in the testosterone-induced maintenance of DSP, the similarity of dose-response curves (ED50 and maximum response) in intact and hypophysectomised rats would suggest that pituitary hormones are not required for this aspect of the process. The observation that the maintenance of DSP by testosterone under some experimental conditions is poorly correlated with interstitial fluid testosterone levels raises questions as to the mechanisms by which testosterone acts to stimulate spermatogenesis.

Animals↗

PubMed1989

Isolation of inhibin alpha-subunit precursor proteins from bovine follicular fluid.

Two proteins with structural characteristics similar to peptide sequences identified in the inhibin alpha-subunit precursor sequence have been isolated from bovine follicular fluid. A side-fraction from the purification of bovine follicular fluid inhibin with high levels of inhibin immunoactivity relative to its inhibin bioactivity was fractionated through a sequence of procedures which included triazine dye affinity and phenyl-Sepharose chromatography, gel permeation chromatography on Sephadex G-100, reverse phase HPLC, and preparative polyacrylamide gel electrophoresis. The first of the two proteins identified had a molecular mass of 25-26K under reducing and nonreducing conditions and a NH2-terminal sequence identical to that of 43K inhibin alpha-subunit and showed minimal activity (less than 2% activity) compared with bovine 31K inhibin in either the inhibin in vitro bioassay or the RIA. These data suggest that this protein is the alpha 1-166 sequence of the bovine inhibin alpha-subunit (designated alpha N-subunit), most likely released after processing of either the inhibin alpha-subunit precursor or the 43K alpha-subunit involved in the conversion of 58K to 31K inhibin. The other protein identified (designated pro-alpha C-subunit) has a molecular mass of 27K under nonreducing conditions and 20K and 6K under reducing conditions. It is inactive in the in vitro bioassay, although highly reactive in the inhibin RIA, and has NH2-termini identical to the pro sequence of the inhibin alpha-subunit precursor and the 20K alpha-subunit sequence. These results suggest that pro-alpha C is a disulfide-linked structure and may represent an intermediate in the dimerisation of alpha- and beta-subunits to form inhibin while the alpha N-subunit is probably a proteolytic product of either the alpha-subunit precursor or 58K inhibin.

Animals↗

PubMed1989

A comparison of the suppressive effects of testosterone and a potent new gonadotropin-releasing hormone antagonist on gonadotropin and inhibin levels in normal men.

GnRH antagonists have been developed in large part because of their potential use as contraceptive agents, particularly in men. Specifically, it was hoped that GnRH antagonists combined with testosterone (T) would be a more effective contraceptive regimen than T alone. We compared the suppressive effects of a potent GnRH antagonist, Na1-Glu [AcD2NaL1,D4ClPhe2,D3Pal3,Arg5,DGlu6(AA),+ ++DAla10-GnRH], and of T together and separately on serum and urinary gonadotropin and serum inhibin levels in normal men. Ten-day courses of Nal-Glu (75 micrograms/kg; Nal-Glu alone), 200 mg testosterone enanthate, im, on days 0 and 7 (T alone), and the combination (Na1-Glu + T) were given to nine men. Serum gonadotropin and inhibin concentrations decreased after 1-2 days of Na1-Glu administration, while gonadotropin suppression occurred more slowly after T alone. Serum T fell to 30% of baseline values during Na1-Glu administration. The combination of Na1-Glu + T was more effective in suppressing serum LH, FSH, and inhibin than was either Na1-Glu alone or T alone. All hormone levels returned to baseline levels within 2.5 weeks after the end of the three regimens. We conclude that the Na1-Glu GnRH antagonist effectively inhibits gonadotropin, inhibin, and sex steroid secretion when given daily for 10 days and that the administration of Nal-Glu + T results in more complete gonadotropin and gonadal suppression than that produced by either agent given alone. These results encourage further investigation of the combination of a GnRH antagonist and T as a male contraceptive regimen and of the antagonist alone as a treatment for hormone-dependent neoplasia.

Adult↗