STIMULATORY AND INHIBITORY FACTORS OF LEYDIG-CELL STEROIDOGENESIS ARESECRETED 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 Sta ges VII-VIII and Stages IX-VI) cultured with or without follicle-stimu lating hormone (FSH) on the production of testosterone and immunoactiv e inhibin by Leydig cells was examined. Low doses of conditioned mediu m 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-st imulated testosterone production by 13+/-7%. Low doses of conditioned medium from unstimulated tubules at Stages IX-VI increased the mean te stosterone production to 22+/-10%, whereas at higher doses, a signific ant reversal in the stimulation occurred although not to the same exte nt as that found with medium from tubules at Stages VII-VIII. Conditio ned medium from FSH-stimulated tubules at Stages VII-VIII and Stages I X-VI, significantly increased testosterone production to 39+/-7% and 3 1+/-13% respectively. Immunoactive inhibin production by the Leydig ce lls remained unaffected by exposure to conditioned medium from FSH sti mulated 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 th e contradictory reports in the literature.