Regulatory effects of steroids on the pituitary response to LH-RH

Abstract

The pituitary response to a continuous i.v. LH-RH administration (15 [mu]g/h/3 h) associated with physiological or pharmacological doses of several steroid hormones such as estradiol (E2), progesterone, 17[alpha]OH-progesterone, 20[alpha]OH-progesterone, chlormadinone acetate, testosterone (T) and 5[alpha]-dihydrotestosterone (5[alpha]DHT) was evaluated by radioimmunoassayable plasma LH and FSH measurements, in normal and post-menopausal women, normal men, and in a Flinefelter's syndrome subject. Analysis of results indicated that E2 in doses of 132[mu]g/h/6 hs blocks the pituitary response to LH-RH in all cases except in the Klinefelter's syndrome patient. Nevertheless, E2 in doses of 6.6 [mu]g/h/6 hs did not cause a significant inhibitory effect. The infusion of physiological (330 [mu]g/h/6 hs) or pharmacological (3300-6600 [mu]g/h/6 hs) doses of any of the selected progestational steroids did not block the pituitary response to LH-RH. When chlormadinone acetate was infused together with E2 in normal and postmenopausal women, the inhibitory effect of E2 on the pituitary response to LH-RH was antagonized. T in doses of 600 [mu]g/h/6 hs produced a partial inhibitory effect on the pituitary response to LH-RH in normal men, nevertheless in the post-menopausal women and in the Klinefelter's syndrome patient did not cause inhibition. 5[alpha]DHT did not inhibit the pituitary response to LH-RH administration in all subjects tested. It was concluded that: (1) pharmacological doses of E2 completely blocks the pituitary response to LH-RH; (2) the inhibitory effect of E2 was counteracted by chlormadinone acetate; (3) the infusion of T produced a partial inhibitory effect on the pituitary response to LH-RH in normal men, and (4) in the patient with Klinefelter's syndrome, the infusion of pharmacological doses of T and E2 did not inhibit the LH pituitary response to LH-RH.