A reinvestigation of hypothalamic-pituitary testicular interactions : simultaneous changes in tissue and plasma levels of gonadotrophins, prolactin, testosterone and hypothalamic LH-RH after bilateral orchidectomy and cryptorchidism

Plasma concentrations of LH, FSH, prolactin and testosterone, pituitary concentrations of gonadotrophins and prolactin, and hypothalamic LH-RH were measured in normal, sexually mature male rats at regular intervals from 1 to 30 days after castration or cryptorchidism. Bilateral castration resulted in a marked decrease in testosterone levels 24 h after surgery. On the contrary, plasma testosterone was increased (at days 4 and 8) or unaffected by cryptorchidism when compared to intact controls. From day 1, castrated rats showed a rapid, marked increase in plasma LH and FSH (7 and 5 times higher at day 30 for LH and FSH, respectively) and a delayed, progressive increase in pituitary gonadotrophins (significant at day 8 and day 30 for LH and FSH, respectively). The cryptorchid animals showed similar but slower and less marked changes in plasma and pituitary FSH and LH levels. Unlike plasma prolactin levels, which were lowered at day 8 or days 4, 8 and 30, respectively, after castration or cryptorchidism, no change was observed in pituitary prolactin content. After castration, hypothalamic LH-RH content was significantly lower at day 4 and gradually decreased until day 30. On the other hand, no changes were observed after cryptorchidism. The present observations indicate that factors other than testosterone, associated with the presence of an active seminiferous epithelium, are involved in the regulation of gonadotrophin secretion. These factors do not seem to change the hypothalamic LH-RH content.