Blockade of the oestrogen-induced LH surge in the ovariectomized common marmoset (Callithrix jacchus) by an LHRH antagonist

Abstract

Summary. Six long-term ovariectomized adult marmoset monkeys were treated at 0 h with 35 \g=m\g 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 \g=m\g/kgs.c., or received the detirelix vehicle alone at 0 h, 12h 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\p=n-\12h 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\m=.\0 \ m=+-\ 5\m=.\8at 0 h to 12\m=.\8 \ m=+-\ 2\m=.\6 ng/ml at 6 h (negative feedback), followed by a positive feedback surge, reaching a maximum of 148\m=.\0\m=+-\ 34\m=.\6ng/ml at 24h. Values then declined to pretreatment levels by 56h. 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\p=n-\72h.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.

Pituitary-testicular function is suppressed by an LHRH antagonist but not by an LHRH agonist in the marmoset monkey

“…This ability of the antagonist to inhibit pituitary-testicular function agrees with pre¬ vious reports in the female marmoset (Hodges, Green, Cottingham et al 1988;O'Byrne, Lunn & Fraser, 1989) and is similar to observations in Old World primates, man and other mammalian species (Adams, Bremner, Nestor et al 1986;Pavlou, Debold, Island et al 1986). …”