Steroidal modulation of pituitary gonadotropin-releasing hormone responsiveness in young turtles, Pseudemys scripta.

Steroid-modulated pituitary secretion and glandular content of gonadotropin (Gth: LH and FSH) was studied in young slider turtles. Injection (ip) of both 17 beta-estradiol (E2) and testosterone (T) reduced pituitary content of both Gths and caused significant inhibition of basal LH secretion and gonadotropin-releasing hormone (GnRH)-stimulated LH and FSH secretion measured in vitro. However, gonadectomy did not affect pituitary Gth secretion or response in these juveniles, and anti-estrogen and anti-androgen compounds had some steroid agonistic action on the pituitary gland. Exposure to E2, T, and 5 alpha-dihydrotestosterone (DHT) in vitro for 4, 24, or 48 hr either had no effect or completely inhibited pituitary GnRH responsiveness. Progesterone (P) alone had no effect on pituitary GnRH response and in combination did not alter the typical inhibitory effect of E2. There were several indications of differential effects of steroids on secretion of the two Gths, especially in response to GnRH and tetraethyl chloride (receptor independent) stimulation. The results suggest that steroids may act directly at the pituitary level to alter Gth secretion and that steroidal modulation of pituitary secretion might play a role in differential regulation of LH and FSH in turtles.