Secretion of lh, fsh and oestradiol-17β during the follicular phase of the oestrous cycle in the ewe

Abstract

Plasma concentrations of LH, FSH and oestradiol-17β 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. © 1988 ASEG.