Changes in testicular inhibin after a single episode of heating of rat testes.

Brief heating (43 C for 15 min) of the scrota of adult rats was used to induce reversible spermatogenic damage to the testes. In these animals the changes in testicular inhibin content and an index of inhibin production rate, measured after efferent duct ligation, were examined and correlated with serum gonadotropin levels. The effect of heating was not evident until after 1 week when testis weight, inhibin content, and inhibin production rate were significantly reduced and both serum FSH and LH were elevated. By 2 weeks, the maximal effects were observed, and, thereafter, all parameters gradually returned to control values (FSH: by 6 weeks; testis and epididymal weight, inhibin content, inhibin production rate, and seminiferous tubule fluid production: by 17 weeks). Throughout the study, serum testosterone levels showed no significant changes. Significant inverse correlations were found between serum FSH levels and inhibin content (r = -0.502, P less than 0.001) or inhibin production rate (r = -0.533, P less than 0.001), and these were taken as supportive evidence for the hypothesis that inhibin is involved in the feedback control of pituitary FSH secretion. Although serum LH levels were also negatively correlated to the corresponding inhibin content (r = -0.669, P less than 0.001) or inhibin production rate (r = -0.420, P less than 0.001), recent findings of Leydig cell dysfunction in these animals led us to relate the transient rise in LH to the altered state of Leydig cell function.