Effects of Gonadal Steroids on the Basal and LRF-Induced Gonadotropin Secretion by Cultures of Rat Pituitary1

The effects of 17beta-estradiol (E2), progesterone (P4), 20alpha-hydroxypregn-4-en-3-one (20alpha-OHP4), and testosterone (T) on the basal and LRF-induced secretion of LH and FSH were studies in monolayer cultures prepared from the pituitaries of adult female rats. Day 4 cultures were used and all steroids were tested at 10-8M concentration for 4 hr. E2 (2.72 ng/ml) alone caused a nonsignificant increase in basal secretion of both LH and FSH; however, the same dose of E2 significantly (p less than 0.001) inhibited the LRF-induced secretion of LH but not of FSH (74% and 88% of 10-8M LRF-treated level, respectively), Testosterone (2.88 ng/ml) alone significantly increased the basal secretion of LH (136% of control level, p less than 0.05) and augmented the effect of LRF on FSH secretion to 130% of the LRF-treated level (p less than 0.05). Contrary to its negative feedback action on the basal secretion of FSH (46% of control level, P less than 0.05), 20ALPHA-OPH4 (3.15 ng/ml) augmented the effect of LRF on LH secretion (130% of LRF-treated level, P less than 0.05). On the other hand, P4 (3.14 ng/ml) did not cause any significant inhibition in the basal and LRF-induced secretion of either LH or FSH. These data indicate that both of the LH- and FSH-LRF; however, their secretory activities are modulated differently by various steroids.