Secretion of LH, FSH and Oestradiol-17ß During the Follicular Phase of the Oestrous Cycle in the Ewe

Abstract

Plasma concentrations of LH, FSH and oestradiol-17iJ were measured in blood samples taken at 15 min intervals for 48 h during the follicular phase of four Merino ewes. The amplitude of pulses of LH and the mean concentration of LH were higher at the beginning of the follicular phase, 36-24 h before the preovulatory surge of LH (amplitude 2·4 ng ml- 1, mean concentration 3·9 ng ml- 1), than at the end, 24-0 h before the preovulatory surge (amplitude 1· 2 ± 0·1 ng ml- 1; mean concentration 1·4 ± 0·1 ng ml- 1). There was no change in the inter-pulse interval during this time (mean 74 ± 5 min). Over the same period, oestradiol levels increased from 7-8 pg ml- 1 to a peak of 10- 15 pg ml- 1. Mean FSH concentrations declined (36-24 h: 3· 6 ng ml - 1 vs 24-0 h: 1· 8 ± O· 3 ng ml- 1) before rising at the time of the preovulatory surge of LH and again 24 h later. It was concluded that the biphasic response of LH to oestrogen that is seen in ovariectomized ewes may also operate during the follicular phase of the oestrous cycle in entire ewes.