Relationship between the exposure of Leydig cells to factor(s) present in testicular interstitial fluid and changes in their capacity to secrete testosterone during culture or after hCG-induced desensitization.

This study has evaluated whether the decrease in capacity of Leydig cells to secrete testosterone that occurs during culture or after desensitization with hCG in vivo, is a consequence of the removal of a stimulatory factor(s) in testicular interstitial fluid (IF) to which Leydig cells are normally exposed. When Percoll-purified rat Leydig cells were cultured for 3 days in vitro, there was a progressive reduction in their ability to respond to hCG in terms of either testosterone or progesterone production. In contrast, culture of the cells in the presence of 10% charcoal-stripped IF maintained responsiveness to hCG either partially or completely. This effect was attributable to a factor(s) in IF with a molecular weight of greater than 30 kDa; a comparable fraction from serum had little or no effect. Crude Leydig cells from rats injected 24 h previously with 50 IU hCG showed a 70% reduction in their testosterone response to hCG in vitro and, compared to controls, increased testosterone production poorly in response to increasing concentrations of IF. However, progesterone secretion was increased considerably in response to IF. As in controls, fractionation of crude Leydig cells from hCG-desensitized rats on Percoll gradients resulted in three bands of Leydig cells, except that the yields of band 2 and 3 cells (containing about 40 and 85% Leydig cells, respectively) were reduced by 75% and 90%, respectively, with the majority of Leydig cells remaining in band 1 (which comprises poorly responsive cells). Band 2 and 3 cells from hCG-desensitized rats were not greatly different to cells from control rats in terms of their testosterone response to hCG +/- IF, although they produced considerably more progesterone. It is concluded that the reduced capacity of Leydig cells to secrete testosterone during culture may be attributable to some extent to the removal of a factor(s) in IF to which the cells are normally exposed. In contrast, the reduced in vivo exposure of Leydig cells to such factors, as occurs after hCG injection, cannot explain the poor testosterone response of these cells when they are isolated and cultured.