title: Possible site of negative and positive feedback action of oestrogen on gonadotrophin secretion in normal women.
abstract: For determination of the site of action of oestrogen (E) during the negative and positive feedback phases of gonadotrophin secretions, studies were made on the pituitary response to a small amount of LRH and the pulsatility of gonadotrophins after E administration in normal cycling women in the mid-follicular phase. The pituitary responses to an iv bolus of 2.5 micrograms of synthetic LRH 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 less than 0.05) decreased 8 h after E injection, but were significantly (P less than 0.05) increased 56 h after E administration. In the third cycle, the pulsatility of gonadotrophins 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 gonadotrophins 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. These findings suggest that the negative and positive feedback effects of E on gonadotrophin secretion may be caused, in part, by its direct action on the pituitary response to LRH.
authors.forename: Y
authors.initials: Y
authors.lastname: Nagahara
authors.forename: A
authors.initials: A
authors.lastname: Miyake
authors.forename: K
authors.initials: K
authors.lastname: Tasaka
authors.forename: Y
authors.initials: Y
authors.lastname: Kawamura
authors.forename: T
authors.initials: T
authors.lastname: Aono
authors.forename: O
authors.initials: O
authors.lastname: Tanizawa
mesh_terms: D000328:Adult; D004966:Estrogens, Conjugated (USP) / Q000494:pharmacology*; D005246:Feedback; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D005498:Follicular Phase; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*
chemical_list: D004966:Estrogens, Conjugated (USP); D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone