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M Benahmed

Publications and source records attributed to M Benahmed.

98 records · Page 6Linked to original sources
PubMed1983

Steroidogenesis of cultured purified pig Leydig cells: effects of lipoproteins and human chorionic gonadotropin.

Dispersed Leydig cells were prepared from pig testes and purified in a discontinuous Percoll gradient. About 95% of these cells stained for 3 beta-hydroxysteroid dehydrogenase. The cells were cultured in a chemically defined medium. Testosterone production was low (2 +/- 0.4 ng/10(6) cells/day) under basal conditions, but increased by 8- to 10-fold on the third day of daily human CG (hCG) treatment. Addition to the medium of both human and pig low density lipoprotein (LDL) produced a dramatic increase in both basal (8-fold) and acute hCG-stimulated (5-fold) testosterone production, whereas both human and pig high density lipoprotein were far less effective. Furthermore the effect of lipoproteins was synergistic with that of hCG. The effects of human LDL on both basal and hCG-stimulated testosterone productions were dose-dependent. Maximum effect was achieved at a protein concentration of 10-40 micrograms/ml with an ED50 of about 4 micrograms/ml. Three days of pretreatment with hCG or (Bu)2cAMP alone induced Leydig cell steroidogenic refractoriness to both hCG and (Bu)2cAMP stimulation. Concomitant treatment with LDL restored the steroidogenic capacity, but only partially. Production of pregnenolone and testosterone of desensitized cells was significantly higher than that of control cells under basal conditions, but was 60% and 40% lower, respectively, after acute hCG stimulation. Moreover, the conversion of exogenous pregnenolone to testosterone by desensitized cells was only 60% of that of control cells. These results show that the de novo synthesis of cholesterol is able to account for only 25% of the maximal steroidogenic capacity of pig Leydig cells and that hCG-induced steroidogenic desensitization is only partially due to cholesterol depletion.

Animals↗
PubMed1983

Hormonal regulation of pig Leydig cells in culture.

Using a primary culture of purified immature pig Leydig cells, the hormonal and non hormonal regulation of steroidogenic activity have been studied. The effects of LH/hCG, FSH, LHRH, o-prolactin, estradiol, epidermal growth factor (EGF), human low density lipoprotein (hLDL) and human high density lipoprotein (hHDL) on 125I-hCG binding and basal and hCG-stimulated cAMP and steroids (testosterone and dehydroepiandrosterone sulfate) production were evaluated. These data on the regulation of pig Leydig cell activity are compared with other published results, mainly in the rat model, obtained either in vivo and in vitro.

Animals↗
PubMedDate not supplied

Steroidogenesis of cultured purified pig Leydig cells: secretion and effects of estrogens.

Using a primary culture of purified immature pig Leydig cells we have demonstrated: (1) that during the first 3 days of culture there is a 'spontaneous' maturation of the steroidogenic response to hCG, as expressed by a 50-fold increase of the steroidogenic capacity, an increased secretion of both dehydroepiandrosterone sulfate (DHAS) and testosterone (T), a shift of the DHAS/T ratio (5 on day 0 vs. 0.5 on day 3) without significant changes in the number of hCG-binding sites; (2) that purified cells, on day 3 following hCG stimulation, secrete large amounts of T and small amounts of E2 (T/E2 congruent to 150) and detectable amounts of estrone, while crude pig interstitial cells under the same conditions secrete less T but 40-50 times more estrogens (T/estrogens congruent to 1.5); (3) that the steroidogenic responsiveness of purified Leydig cells is not impaired by E2 treatment, in spite of the fact that Leydig cells contain specific estradiol receptors (approximately 10000 sites/cell). These data suggest that in this model the main source of testicular estrogens are not Leydig cell but some other testicular cell types, and that the lack of effect of estrogens on pig Leydig cell steroidogenesis is not due to absence of estrogen receptors.

Androgens↗
PubMedDate not supplied

Stem cell factor/c-kit system in spermatogenesis.

One of the major unresolved questions with male infertility is the identification of the molecular origin of a great majority of the spermatogenetic arrests currently diagnosed as idiopathic male infertility. During the past years, several families of regulating factors have been implicated in spermatogenesis defects observed essentially in animal models. Among these factors are signalling molecules, and particularly the stem cell factor (SCF)/c-kit system. The SCF and its receptor c-kit are an appropriate example to illustrate the role of signalling molecules in the physiology and pathology of spermatogenesis. The SCF/c-kit regulates primordial germ cell migration, proliferation and apoptosis during fetal gonadal development. The SCF/c-kit also regulates spermatogonia proliferation in the adult animal. In mutant mice, abnormalities of the SCF/c-kit gene expression, such as gene deletion, point mutation, alternative splicing defect, lead to different types of spermatogenesis alterations (e.g. decrease in primordial germ cell migration, decrease in spermatogonia proliferation). More recently, defects in SCF/c-kit gene expression have also been shown in human testicular dysfunctions. Indeed, a reduction in SCF/c-kit expression has been evidenced in oligozoospermia/azoospermia associated with an increase in the germ cell apoptosis process. In addition, c-kit seems to be a good marker of seminoma testicular tumours. This review reports a large number of data--obtained essentially in animal models--that suggest an important role for the SCF/c-kit system in spermatogenesis and, as a corollary, its potential involvement in spermatogenic defects.

Animals↗
PubMedDate not supplied

[Role of plasma lipoproteins in the function of steroidogenic tissues].

Steroidogenic cells (adrenal, gonads and placenta) utilize cholesterol as a substrate for hormonal biosynthesis. Cholesterol can be synthetized de novo acetate or can enter the cell as a component of plasma lipoproteins, particularly LDL (low density lipoprotein) and HDL (high density lipoprotein). Steroidogenic cells utilize predominantly lipoproteins. Lipoprotein-cholesterol enters the cell by a specific pathway: binding of lipoproteins, particularly LDL to a membrane specific receptor and internalization of the complex receptor-lipoprotein, followed by dissociation of the complex; the receptor is reutilized, while LDL is hydrolyzed by lysosomal enzymes in amino-acids and free cholesterol. The liberated cholesterol is available for utilization by the cell. In addition, lipoproteins modulate intra-cellular cholesterol metabolism via two enzymatic activities; inhibition of hydroxymethyl-glutaryl coenzyme A reductase activity (HMG CoA reductase) which controls the rate limiting step of cholesterol biosynthesis, and stimulation of acyl CoA cholesterol acyltransferase (ACAT) activity which controls the esterification of cholesterol, before its translocation to lipids droplets. Peptide hormones LH/hCG and ACTH regulate lipoproteins metabolism in their target tissues by increasing LDL receptors number, a way which allow more cholesterol to enter the cell. The role of lipoproteins on steroidogenesis has been studied predominantly in adrenal and to a lesser extent in ovary and placenta and poorly in testis. Using a model of cultured porcine Leydig cells, we have demonstrated that de novo synthesis of cholesterol accounts for only 25% of the maximal steroidogenic capacity of these cells. Moreover the effects of lipoprotein LDL was synergistic with that of gonadotropins.

Adrenal Cortex↗
PubMedDate not supplied

[Role of tumor necrosis factor in the male gonad].

Within the male gonad, TNF alpha is secreted by macrophages in the interstitial tissu and by germ cells in seminiferous tubules. TNF alpha receptors (type I) have been detected in the somatic cells of the testis (i.e. Leydig and Sertoli cells). TNF alpha has two type of action within the testis: the cytokine has an anti-hormonal role and play a role in the interactions between Sertoli and germ cells. Anti-hormonal actions of TNF alpha are (i) inhibition of LH-induced testosterone production in Leydig cells and (ii) inhibition of FSH-induced inhibin production in Sertoli cells. Moreover, TNF alpha; produced by germ cells, enhanced expression of growth factors in Sertoli cells (IGFBP3, receptor type I of bFGF) and enhanced production of energetic metabolite important for germ cells such as lactate (via enhancement of lactate dehydrogenase enzyme, isoform 5). Moreover, Fas/Fas ligand system, proteins related to TNF alpha, seem to play a key role in the protection of germ cells against the immune system within the testis. In conclusion, TNF alpha and related proteins, could play a great role in testicular functions such as spermatogenesis (interactions between Sertoli and germ cells) and in the interactions between immune system and spermatogenesis (role of TNF alpha originating form blood/testicular macrophages, role of Fas/Fas ligand system).

Humans↗