Possible site of negative and positive feedback action of oestrogen on gonadotrophin secretion in normal women
Nagahara, Y.; Miyake, A.; Tasaka, K.; Kawamura, Y.; Aono, T.; Tanizawa, O.
Acta Endocrinologica 108(4): 440-444
1985
ISSN/ISBN: 0001-5598 PMID: 2986399 Document Number: 259737
For determination of the site of action of estrogen (E) during the negative and positive feedback phases of gonadotropin secretions, studies were made on the pituitary response to a small amount of LHRH and the pulsatility of gonadotropins after E administration in normal cycling women in the mid-follicular phase. The pituitary responses to an i.v. bolus of 2.5 .mu.g of synthetic LHRH were evaluated by measuring serum LH and FSH 2 h before and 8 h after administration of 20 mg of conjugated E (Premarin). In the next cycle, the pituitary responses to a same dose of LHRH were also observed 2 h before and 56 h after E injection. The mean levels of serum LH and FSH and the peak responses to LRH were significantly (P < 0.05) decreased 8 h after E injection, but were significantly (P < 0.05) increased 56 h after E administration. In the 3rd cycle, the pulsatility of gonadotropins was evaluated by measuring serum LH and FSH every 15 min for 180 min before and 8 h and 56 h after E injection. The pulse frequencies of gonadotropins were not significantly different before and 8 h and 56 h after E injection. The amplitudes of pulses 56 h after Premarin injection were significantly higher than those before the injection. Apparently, the negative and positive feedback effects of E on gonadotropin secretion may be caused, in part, by its direct action on the pituitary response to LHRH.