Blockade of the oestrogen-induced LH surge in the ovariectomized common marmoset (Callithrix jacchus) by an LHRH antagonist.
Six long-term ovariectomized adult marmoset monkeys were treated at 0 h with 35 micrograms oestradiol benzoate s.c. to induce an LH surge. They were also treated with detirelix (an LHRH antagonist) at 0 h, 12 h and 24 h (Exp. 1), or at 0 h and 24 h (Exp. 2) at a dose of 300 micrograms/kg s.c., or received the detirelix vehicle alone at 0 h, 12 h and 24 h (Exp. 3). All animals received the three treatments, with at least 4 weeks between experiments. Blood samples were collected at 0 h and at 6-12 h intervals for 72 h after oestradiol for the determination of plasma LH by bioassay. In control animals, oestrogen treatment resulted in a decline in plasma LH from 30.0 +/- 5.8 at 0 h to 12.8 +/- 2.6 ng/ml at 6 h (negative feedback), followed by a positive feedback surge, reaching a maximum of 148.0 +/- 34.6 ng/ml at 24 h. Values then declined to pretreatment levels by 56 h. In contrast, antagonist-treated animals showed complete abolition of the expected increase at 24 h, the low levels of the negative feedback phase being maintained for 36-72 h. These results show that hypothalamic LHRH release is essential during the oestrogen-induced LH surge, and that a direct oestrogen-induced component at the pituitary level is not expressed in the absence of LHRH in the marmoset.
O'Byrne
K T
KT
MRC Reproductive Biology Unit, Centre for Reproductive Biology, Edinburgh, UK.
Lunn
S F
SF
Fraser
H M
HM
D000818:Animals; D002144:Callithrix; D004958:Estradiol; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood*; D010052:Ovariectomy; D011966:Receptors, LHRH / Q000187:drug effects
D011966:Receptors, LHRH; C043699:detirelix; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone