An ultrasound-aided study of temporal relationships between the patterns of LH/FSH secretion, development of ovulatory-sized antral follicles and formation of corpora lutea in ewes

To characterize the pulsatile secretion of LH and FSH and their relationshi ps with various stages of follicular wave development (follicles growing fr om 3 to greater than or equal to 5 mm) and formation of corpora lutea (CL), 6 Western white-faced ewes underwent ovarian ultrasonography and intensive blood sampling (every 12 min for 6 h) each day, for 10 and 8 consecutive d ays, commencing 1 and 2 d after estrus, respectively. Basal serum concentra tions of LH and LH pulse frequency declined, whereas LH pulse duration and FSH pulse frequency increased by Day 7 after ovulation (P<0.05). LH pulse a mplitude increased (P<0.05) at the end of the growth phase of the largest o varian follicles in the first follicular wave of the cycle. The amplitude a nd duration of LH pulses rose (P<0.05) 1 d after CL detection. Mean and bas al serum FSH concentrations increased (P<0.05) on the day of emergence of t he second follicular wave, and also at the beginning of the static phase of the largest ovarian follicles in the first follicular wave of the cycle. F SH pulse frequency increased (P<0.05) during the growth phase of emergent f ollicles in the second follicle wave. The detection of CL was associated wi th a transient decrease in mean and basal serum concentrations of FSH (P<0. 05), and it was followed by a transient decline in FSH pulse frequency(P<0. 05). These results indicate that LH secretion during the luteal phase of th e sheep estrous cycle reflects primarily the stage of development of the CL , and only a rise in LH pulse amplitude may be linked to the end of the gro wth phase of the largest follicles of waves. Increases in mean and basal se rum concentrations of FSH are tightly coupled with the days of follicular w ave emergence, and they also coincide with the end of the growth phase of t he largest follicles in a previous wave, but FSH pulse frequency increases during the follicle growth phase, especially at mid-cycle. (C) 2000 by Else vier Science Inc.