Stimulatory and inhibitory factors of leydig cell steroidogenesis are secreted simultaneously by the rat seminiferous tubules and do not affect leydig cell inhibin production in vitro

The effect of conditioned medium from rat seminiferous tubules (at Stages VII-VIII and Stages IX-VI) cultured with or without follicle-stimulating hormone (FSH) on the production of testosterone and immunoactive inhibin by Leydig cells was examined. Low doses of conditioned medium from unstimulated tubules at Stages VII-VIII significantly (P < 0-05) increased the mean testosterone production to greater than 31±11% over that achieved with luteinizing hormone (LH) alone. At the highest dose, the conditioned medium significantly inhibited (P < 0-05) LH-stimulated testosterone production by 13±7%. Low doses of conditioned medium from unstimulated tubules at Stages IX-VI increased the mean testosterone production to 22±10%, whereas at higher doses, a significant reversal in the stimulation occurred although not to the same extent as that found with medium from tubules at Stages VII-VIII. Conditioned medium from FSH-stimulated tubules at Stages VII-VIII and Stages IX-VI, significantly increased testosterone production to 39±7% and 31±13% respectively. Immunoactive inhibin production by the Leydig cells remained unaffected by exposure to conditioned medium from FSH stimulated and unstimulated tubules at Stages VII-VIII and Stages IX-VI. The data demonstrate that tubule culture medium contains FSH-modulated activities which can specifically stimulate and inhibit testosterone synthesis by adult rat Leydig cells in vitro and therefore explains the contradictory reports in the literature.