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G Verhoeven

Publications and source records attributed to G Verhoeven.

At least 145 records · Page 8Linked to original sources
PubMed1986

The dynamics of steroid and adenosine 3',5'-cyclic monophosphate output in perifused interstitial cell aggregates derived from prepubertal rat testes.

The characteristics of the steroidogenic response of reaggregated rat interstitial cells were examined in a perifusion system. Interstitial cells were isolated from 19-day-old rat testes by digestion with collagenase. The cells were cultured for 3 days as monolayers and were resuspended by brief treatment with trypsin. Constant gyratory shaking of the dispersed cells resulted in the formation of round and compact aggregates of 70-140 microns. The functional characteristics of these aggregates were examined by studying the output of cAMP, C19 steroids (testosterone and androstenedione), and C21 steroids (progesterone, 17 alpha-hydroxyprogesterone, 20 alpha-hydroxypregn-4-en-3-one) in a perfusion system. It is demonstrated that reaggregated interstitial cells maintain their responsiveness to LH, LHRH, and Leydig cell stimulatory factor(s) produced by Sertoli cells for at least 12 days. When exposed to low concentrations of LH (1 ng/ml), either in a continuous or in a pulsatile fashion, perifused aggregates maintain a constant output of steroids for more than 20 h. Under these conditions, LH-dependent differentiation of the steroidogenic machinery can be observed in vitro. In fact, although the sum of the measured steroids remains constant, C21 steroids progressively decrease whereas C19 steroid output increases during perifusion. When perifused with high concentrations of LH (10 ng/ml), desensitization becomes the predominant phenomenon. It is demonstrated that the steroid output of reaggregated interstitial cells considerably exceeds that of similarly treated cells maintained as monolayers. Moreover, perifusion of aggregates results in a 6-fold increase in steroid output as compared to static incubation and in a selective increase in androgen output. It is concluded that prepubertal interstitial cells allowed to reaggregate in suspension culture form functional multicellular structures. Perifusion of these aggregates is a useful tool in the study of the dynamics of the regulation of steroidogenesis.

Animals↗
PubMed1985

Influence of neonatal androgenization on the expression of alpha 2u-globulin in rat liver and submaxillary gland.

We studied the influence of neonatal androgenization on the serum level of alpha 2u-globulin, the level of the corresponding mRNA in liver and submaxillary gland and the concentration of an androgen and oestrogen binding protein in liver cytosol. Male rats gonadectomized on day 15 (after the neonatal surge of androgen secretion) were used as neonatally androgenized animals, their female littermates gonadectomized at the same age served as controls. Using a sensitive radioimmunoassay it could be demonstrated that only very low levels of alpha 2u-globulin are present in adult female control animals. Neonatal androgenization increases these levels some 14-fold. Stimulation with testosterone or dexamethasone results in a relative increase in the serum levels in animals of both sexes. After 11 days of treatment with testosterone propionate or dexamethasone, however, the final alpha 2u-globulin levels are respectively 1.8 times and 8 times higher in neonatally androgenized rats as compared to their female littermates. The concentration of the androgen and oestrogen binding protein in rat liver cytosol displays parallel sex differences in unstimulated animals and parallel changes after treatment with androgens and glucocorticoids. Measurements of alpha 2u-globulin mRNA by dot blot hybridization and by translation in reticulocyte lysate show a good correlation between the serum levels of alpha 2u-globulin and the corresponding mRNA in the liver. The abundance of alpha 2u-globulin mRNA in submaxillary gland is not influenced by neonatal androgens or hormone treatment during adulthood. These data suggest that neonatal androgenization directly or indirectly influences the availability for transcription and/or the transcription rate of alpha 2u-globulin genes in the liver.

Alpha-Globulins↗
PubMed1985

Transcortin and alpha 2u-globulin messenger RNA activities during turpentine-induced inflammation in the rat.

Previously we have shown that the serum concentration of transcortin and alpha 2u-globulin markedly decreases during turpentine-induced inflammation. In the present study transcortin and alpha 2u-globulin mRNA from healthy rats and from animals with inflammation was translated in a rabbit reticulocyte lysate system. Female rats had higher levels of translatable transcortin mRNA than male animals and the level of mRNA for transcortin and alpha 2u-globulin decreased rapidly during inflammation. These results indicate that the sex difference in the serum level of transcortin and the changes in serum transcortin and alpha 2u-globulin during inflammation are mainly determined by differences in the mRNAs in the liver.

Alpha-Globulins↗
PubMed1985

A factor in spent media from Sertoli-cell-enriched cultures that stimulates steroidogenesis in Leydig cells.

We investigated whether Sertoli cell spent media (SCM) contain a factor (or factors) which influences steroidogenesis in Leydig cells. Freshly prepared prepubertal interstitial cells or Percoll-purified Leydig cells and similar cells cultured in the presence or absence of LH were incubated for 24 h in the presence of a 5 alpha-reductase inhibitor and in the presence or absence of SCM. The accumulation of C19-steroids (testosterone and androstenedione), C21-steroids (progesterone, 17 alpha-hydroxyprogesterone and 20 alpha-hydroxypregn-4-en-3-one) and cyclic AMP was measured by radioimmunoassay. It could be demonstrated that SCM contains a factor that stimulates an early step in the steroidogenic pathway but at the same time hampers the conversion of C21-precursors into androgens. In freshly prepared Leydig cells the final effect is a stimulation of the androgen output. In Leydig cells cultured in the absence of LH, mainly C21-steroid output is increased. These biological effects resemble those observed with LHRH and its agonists. The activity of the Sertoli cell factor is not affected by an LHRH antagonist, however, and maximally effective concentrations of the factor and LHRH have additive effects, suggesting that they act by distinct receptor systems. Preliminary characterization shows that the factor in SCM is a thermolabile protein with a MW greater than 10 000. The production of the factor decreases during prolonged culture in serum-free medium. Addition of fetal calf serum causes a marked and dose-dependent increase in the production or activity of the factor. Several permanent cell lines (B16, Bowes, BHK, Ratec, RK13, Vero) produce a factor with comparable biological effects on Leydig cells. Nonetheless, the observation that the production of this factor by Sertoli cell cultures is stimulated by FSH and dbcAMP suggests that, in the testis, it may play a role in the paracrine control of Leydig cell function.

Animals↗
PubMed1985

Endocrine effects of high-dose ketoconazole therapy in advanced prostatic cancer.

The endocrine effects of ketoconazole (400 mg orally every 8 h) were studied in 9 previously untreated patients with advanced prostatic cancer. Five of these patients were followed for 12 months. A rapid fall in the serum concentration of testosterone was noted in all patients studied. Minimal values were observed on day 4 of treatment but thereafter serum testosterone increased slowly. The effect of the drug on unbound testosterone was relatively more important, since sex hormone binding globulin increased markedly during treatment. An increase in progesterone and LH was observed in all patients. This suggests that ketoconazole limits the conversion of C21-precursors into androgens. This block is compensated in part by activation of the hypothalamo-hypophyseal feedback system. Urinary 17-ketosteroids were decreased but 17-hydroxysteroids were unaffected by the treatment. In 5 patients followed monthly over a period of 12 months the mean testosterone concentration ranged from 69 ng/100 ml in one patient to 428 ng/100 ml in another. An excellent inverse correlation could be demonstrated between the mean serum concentration of testosterone and the mean concentration of ketoconazole. The change of serum dehydroepiandrosterone sulphate also correlated inversely with the mean ketoconazole level. Increased concentrations of oestradiol were noted in 2 patients with slight gynaecomastia. It is concluded that long-term suppression of androgen production can be realized by high-dose ketoconazole treatment and that the degree of suppression is proportional to the serum levels of the drug.

17-Ketosteroids↗
PubMed1984

A filter disc assay for the measurement and characterization of androgen-binding protein in unconcentrated media from Sertoli cell-enriched cultures.

As easy, rapid and sensitive assay which permits measurements of androgen binding protein (ABP) in unconcentrated spent media from Sertoli cell cultures is described. The method is based on the adsorption of the 5 alpha-dihydrotestosterone-ABP complex onto DEAE-cellulose filter paper discs at pH 8.5. It is demonstrated that this method permits the characterisation of ABP (ligand specificity, kinetic properties) and represents a useful tool for the study of the effects of various hormones on ABP production by cultured Sertoli cells. When added on day 5 of culture, FSH and other agents that raise intracellular cAMP increase ABP secretion up to 3 times. Natural and synthetic androgens provoke a 1.5-1.8-fold increase. The effects of androgens and FSH are additive and cyproterone acetate blocks the effects of androgens in the presence as well as in the absence of FSH.

Androgen-Binding Protein↗
PubMed1984

Androgen and progestogen production by prepubertal rat interstitial cells: study of the effects of LHRH and its analogues and their interactions with LH.

The effects of luteinizing hormone-releasing hormone (LHRH) and an agonistic analogue (LHRHa) have been examined in freshly isolated prepubertal rat interstitial cells and in cells precultured for 6 days in the presence or absence of luteinizing hormone (LH). C19-steroid output (testosterone and androstenedione), C21-steroid output (mainly progesterone and 20 alpha-hydroxypregn-4-en-3-one) and cyclic AMP secretion were used as parameters of interstitial cell activity. A potent 5 alpha-reductase inhibitor was added to the incubation media to simplify the pattern of steroid secretion. It could be demonstrated that LHRHa uniformly stimulates C21-steroid production whereas C19-steroid output is increased only in freshly isolated cells and in cells precultured with LH. At suboptimal concentrations of LH, LHRH and its agonist again uniformly potentiate C21-precursor production whereas LH-induced androgen production is slightly inhibited in freshly isolated cells, strongly inhibited in cells precultured in the absence of LH and markedly enhanced in cells precultured in the presence of LH. The concentrations (ED50 values) of the oligopeptides required to elicit these synergistic or antagonistic effects with LH are lower than those required for their direct effects. An antagonistic LHRH analogue blocks all the stimulatory and inhibitory activities of LHRHa. None of these activities is accompanied by noticeable changes in cyclic AMP secretion. Evidence is presented that LHRH and its agonistic analogue have a stimulatory effect early in the steroidogenic pathway and an inhibitory effect at the level of the conversion of C21-precursors into androgens. Our data suggest that the existing level of 17 alpha-hydroxylase and/or 17,20-desmolase activity is the major factor that determines the ultimate effect of LHRHa on androgen secretion.

Androgens↗
PubMed1983

Heterogeneity of alpha 2u-globulin gene products in different translational systems, plasma and urine.

alpha 2u-Globulin, an androgen dependent rat urinary protein, displays considerable microheterogeneity. To explore whether this microheterogeneity of alpha 2u-globulin in male rat urine is related to the heterogeneity at the level of the genes encoding this protein, or whether it is due to post-translational processing we studied the alpha 2u-globulin mRNA translation products in rabbit reticulocyte and Xenopus oocytes. Comparison of the alpha 2u-globulin species produced in these two heterologous systems with those observed in plasma and urine indicates that the heterogeneity of this protein in urine is mainly due to heterogeneity at the level of the corresponding mRNAs.

Alpha-Globulins↗
PubMed1983

Different forms of alpha 2u-globulin in male and female rat urine.

alpha 2u-Globulin is usually considered to be present only in male rat urine. This study demonstrates that a very similar protein exists in female rat urine and compares its properties with those of the male form. Isoelectric focusing followed by immunofixation reveals considerable microheterogeneity of alpha 2u-globulin in male and female rat urine. Important sex differences are noted in the banding pattern. The isoelectric point of the major male component (pI approximately equal to 5.3) is considerably higher than that of the major female components (pI approximately equal to 4.6). In addition, the female form of alpha 2u-globulin has a somewhat higher mobility on sodium dodecyl sulphate/polyacrylamide gel electrophoresis than its male counterpart. These sex differences are preserved after purification of alpha 2u-globulin from male and female rat urine by affinity chromatography and enrichment of the major male and female components by ion-exchange chromatography. Immunologically no differences are observed between these purified components and their amino acid composition reveals only minor differences. A slightly higher carbohydrate content is observed in the major female component than in the major male component. Finally evidence is presented that oestrogen treatment suppresses the male forms of alpha 2u-globulin but has no effect on the female forms. The observed differences between the male and female forms and their different hormonal control suggest that they are encoded by different genes.

Alpha-Globulins↗
PubMed1983

Dicyclohexane derivatives that bind to androgen-binding protein (ABP) also inhibit hormone stimulated aromatase activity in rat Sertoli cells.

Dicyclohexane derivatives are known to inhibit testosterone binding to rat androgen-binding protein (ABP) a secretory product of Sertoli cells. In this paper we show that these compounds also inhibit the aromatization of testosterone by Sertoli cells in response to cyclic AMP and to hormones that act via this nucleotide. The inhibitory activity of the nonsteroidal androgen analogues is dose-dependent and roughly parallels their ability to interfere with the aromatase activity in human placental microsomes and their affinity for ABP. Diethylstilbestrol and mesohexestrol--two nonsteroidal estrogens which resemble the dicyclohexane derivatives--also inhibit aromatase activity in Sertoli cells and placental microsomes. The effects of the synthetic estrogens on Sertoli cells, however, are less specific. Unlike the dicyclohexane derivatives they also block hormone induced activation of the adenylate cyclase. We conclude that dicyclohexane derivatives are representative of a novel series of inhibitors of aromatase activity.

Androgen-Binding Protein↗
PubMed1983

Inhibition by a 4-methyl-4-aza-steroid of NADPH: delta 4-3-oxosteroid-5 alpha-oxido-reductase activity in cultured interstitial cells derived from immature rat testis.

Prepubertal rat testes have high 5 alpha-reductase (delta 4-3-oxosteroid 5 alpha-oxidoreductase) activity and secrete various 5 alpha-reduced androgens. We demonstrate that Na-4-methyl-4-aza-3-oxo-5 alpha-pregnane-20 (S)-carboxylate, a potent inhibitor of the prostatic 5 alpha-reductase, competitively inhibits the microsomal 5 alpha-reductase of rat testis. The apparent Ki for testosterone is 3.5 nM. At a concentration of 5 X 10(-7) M this compound efficiently inhibits the 5 alpha-reductase in cultured interstitial cells derived from prepubertal rats. Testosterone and 4-androstene-3,17-dione are the major androgens produced by these cells in the presence of inhibitor. It is concluded that 4-methyl-4-aza-steroids are a useful tool in the study of steroid secretion by prepubertal Leydig cells.

5-alpha Reductase Inhibitors↗
PubMed1983

Regulation of inhibin secretion by Sertoli cell-enriched cultures.

Sertoli cells secrete a factor which has the same bioactivity as ovine testicular lymph inhibin: it selectively suppresses the secretion of FSH by cultured pituitary cells. We investigated the factors that acutely modulate the secretion of this inhibin by cultured Sertoli cells derived from immature rats. The secretion of inhibin was studied on day 7 of culture after a 24 h period of incubation in the presence or absence of steroids, gonadotrophins and foetal bovine serum, added alone or in various combinations. It could be demonstrated that aromatisable as well as non-aromatisable natural and synthetic androgens promote the secretion of inhibin in a dose-dependent way. FSH and pregnant mare serum gonadotrophin--at concentrations that clearly stimulate Sertoli cell aromatase activity--did not affect basal or androgen-stimulated production of inhibin. hCG was equally uneffective. The effect of androgens was not modified by the addition of an aromatase inhibitor but it was neutralized by the antiandrogen cyproterone acetate. Oestradiol-17 beta did not influence the secretion of inhibin whereas progesterone decreased it. Serum enhanced basal as well as androgen stimulated secretion of inhibin. It is concluded that androgens are the major factor which acutely stimulates the production of Sertoli cell inhibin.

20-alpha-Dihydroprogesterone↗
PubMed1983

Response of transcortin and alpha 2u-globulin to turpentine-induced inflammation in the rat: influence of corticosteroids and prolactin.

Evidence is presented that (transcortin and alpha 2u-globulin react as negative acute-phase proteins in the rat. Thirty-six hours after turpentine injection, the serum concentration of these proteins showed a two- to threefold decrease. Thereafter, transcortin rapidly returned to normal values, whereas alpha 2u-globulin remained low. This reaction pattern was still present after adrenalectomy, adrenalectomy and administration of glucocorticoids, and after treatment with bromocriptine, a suppressor of prolactin secretion. It is concluded that changes in the secretion of glucocorticoids and prolactin are not required for the observed turpentine-induced decrease of transcortin and alpha 2u-globulin.

Adrenalectomy↗
PubMed1982

Androgen and progestogen production in cultured interstitial cells derived from immature rat testis.

Interstitial cells derived from intact immature rats were cultured as monolayers. Their response to gonadotropins was evaluated by radioimmunoassay of 3',5'-cyclic AMP and steroids in the medium. Steroids were measured either directly (testosterone and progesterone) or after previous oxidation and thin layer chromatographic purification of the steroid extracts (4-androstene-3,17-dione, 5 alpha-androstane-3,17-dione, progesterone, 5 alpha-pregnane-3,20-dione). It could be demonstrated that these cells respond to gonadotropins with increased secretion of C19- and C21-steroids for at least 10 days. The total amount of steroids secreted in the medium, however, decreases markedly. During the first days of culture C19-steroid production falls dramatically whereas the secretion of C21 derivatives increases. A major fraction of the extracted steroids has undergone 5 alpha-reduction. A characteristic feature of cultured interstitial cells is the bell-shaped profile of the dose-response curve for gonadotropin stimulated androgen production. This profile is the result of a steroidogenic lesion situated at the level of the 17 alpha-hydroxylase and/or 17,20-desmolase and induced by high concentrations of gonadotropins. Daily changes with medium supplemented with LH or FSH, initiated on day 3 of culture, prevent a further loss of steroidogenic potential, restore the ability to produce C19-derivatives, and tend to normalize the dose-response curve for gonadotropin stimulated production of androgens.

Androgens↗
PubMed1982

Incidence, growth and oestradiol-receptor levels of 7, 12-dimethylbenz (alpha) anthracene-induced mammary tumours in rats: effects of neonatal sex steroids and oestradiol implants.

The effects of neonatally administered steroids on the sensitivity of the mammary gland to tumour induction by 7, 12-dimethylbenz (alpha) anthracene was studied as a model for delayed (de) differentiating effects of steroid hormones. Immediately after birth male and female rats were gonadectomized and treated with testosterone, oestradiol or oil. Control animals were left intact. On day 45 all the gonadectomized animals and some of the control animals received an implant which delivered continuous low levels of oestradiol. The carcinogen was administered on day 55. The administration of an oestradiol implant, which increased prolactin levels in all animals, markedly reduced tumour incidence in intact female rats and increased tumour incidence in intact male rats. Neonatal administration of testosterone or oestradiol did not significantly influence tumour incidence, histopathology or oestradiol responsiveness in neonatally gonadectomized rats but tended to decrease tumour animals suggests that the effects observed by other authors in intact rats are mediated by changes in gonadal secretions. It is concluded that the hormonal environment during and after tumour induction plays a major role in the development of 7, 12-dimethylbenz (alpha) anthracene-induced mammary carcinomas.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1982

Desensitization of FSH-responsive adenylyl cyclase in cultured immature Sertoli cells by homologous hormone.

Sertoli cell monolayers were prepared from 19-day-old rat testes. On day 7 of culture cells were incubated for 24 hr in the presence or absence of ovine follicle stimulating hormone (oFSH). Cells were harvested, and adenylyl cyclase responses of the membrane particles to FSH, human chorionic gonadotropin (hCG), isoproterenol, and fluoride (F-) were examined in the presence of either GTP or the nonhydrolyzable guanylyl nucleotide GMP-P(NH)P. Culturing the cells in presence of FSH caused a hormone specific desensitization of FSH-responsive adenylyl cyclase, whereas responses to isoproterenol and fluoride were unaffected. Activation of Sertoli cell adenylyl cyclase by GTP and GMP-P(NH)P showed no difference between cells preincubated with or without FSH, indicating that FSH did not change the activity of the G/F (or N) component or its interaction with the catalytic subunit of the adenylyl cyclase. FSH-responsive adenylyl cyclase in cultured Sertoli cells has been shown to be selectively desensitized by homologous hormone. The mechanism may involve alteration or loss of the FSH receptor or changes in the "coupling" of the FSH receptors to the G/F component of the adenylyl cyclase, since there was no alteration in the guanylyl nucleotide and fluoride activation.

Adenylyl Cyclases↗