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.

Increased Cardiovascular and Renal Risk Is Associated with Low Nephron Endowment in Aged Females: An Ovine Model of Fetal Unilateral Nephrectomy

“…Taking into account that a 5 year old sheep is still within its reproductive years (prime reproduction age being 3–6 years), it is expected that the animals of this cohort would have undergone periods of estrus (Winter-Fall) and anestrus (Spring-Summer), similar to other sheep. The ages at which the studies were performed in the present study fell within the spring-summer period and whilst in the present study plasma estradiol levels were detected in some animals above the level of assay (∼3–4 pg/ml) at 1 year and 5 years of age, a study performed in Australian merino’s found that plasma estradiol levels are ∼7–8 pg/ml at the onset of estrus and peak at 10–15 pg/ml during the estrous cycle [38]. Therefore, plasma estradiol levels that were detected in some animals at their respective ages are below the aforementioned values indicating all animals were in anestrus at time of study.…”

Prenatal Programming of Reproductive Neuroendocrine Function: The Effect of Prenatal Androgens on the Development of Estrogen Positive Feedback and Ovarian Cycles in the Ewe1

“…This also was an observation made by Clarke et al [7], who noted that the follicular phase of ewes androgenized from Day 50 to Day 100 of gestation was significantly prolonged. Severe abnormalities in the morphology and function of the ovaries of these in utero-androgenized ewes have been documented [13,32], and these abnormalities in folliculogenesis may contribute to the irregular patterns of P secretion that we observed in the present study.…”

“…1). On each occasion, E was administered as four 3-cm Silastic capsules containing crystalline estradiol benzoate (Sigma-Aldrich) placed under the skin of the front axilla to raise E concentrations to late-follicular-phase levels (7-12 pg/ml) [13]. All implants were soaked in water for 24 h before implantation to prevent an acute peak in E concentration [14].…”

Effects of breed, ovarian steroids and season on the pulsatile secretion of LH in ovariectomized ewes

“…Oestradiol. Samples were assayed in duplicate for oestradiol-17ß in chromatographed diethyl ether extracts of 2 ml plasma using a previously described technique (Thomas et a!, 1988). All samples were assayed in one assay (sensitivity 0-50 ± 0-06 pg/ml).…”