Evaluation of the effect of peritubular cell secretions and the testicular paracrine factor P‐Mod‐S on Leydig cell steroidogenesis and immunoactive inhibin production

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Abstract
Testicular peritubular cells have been shown to produce a paracrine factor, termed P-Mod-S, under androgen control that has dramatic effects on Sertoli cell function and may provide an important mode of androgen action in the testis. Therefore, the current study was designed to investigate the possibility that peritubular cell secretory products could feedback and regulate Leydig cell function. The Leydig cell functional parameters that were examined included testosterone production and inhibin secretion. Purified forms of P-Mod-S (P-Mod-S(A) and P-Mod-S(B) shown to be biologically active on Sertoli cells) had no effect on basal or gonadotrophin-stimulated production of testosterone or inhibin by Leydig cells. A preparation of peritubular cell-secreted proteins (PSP) with molecular weights greater than 3 kDa did not influence testosterone production by Leydig cells. PSP, however, did influence cultured Leydig cell morphology and improved cell viability. PSP also had no effect on the ability of LH to stimulate Leydig cell testosterone production. Whilst determining the effect of PSP on Leydig cell inhibin production, PSP was found to contain endogenous levels of inhibin apparently due to 2% contamination of the peritubular cell cultures with Sertoli cells. When this endogenous inhibin level was considered, PSP was found to have no influence on basal or hormone-stimulated production of inhibin by Leydig cells. Results of the current study indicate that peritubular cell secretory products, including the paracrine factor P-Mod-S, do not appear to play a major role in the regulation of Leydig cell function. Therefore, the regulation of Leydig cell function by the seminiferous tubule will primarily be due to Sertoli cell secretory products.

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