Pulsatile release of luteinizing hormone and the secretion of ovarian steroids in sheep during anestrus

Abstract

The peripheral concentration of LH and the secretion rates of estradiol-17beta and androstenedione were measured every 10 min for 4 h during anestrus in six ewes with utero-ovarian autotransplants. The basal concentration of LH was 0.45 +/- 0.06 ng//ml (NIH LH S14; mean +/- SEM), with pulses of LH (6.0 +/- 0.3 ng/ml; N = 5) occurring with an average frequency of one per 5 h. The basal secretion rate of estradiol-17beta was 0.5--1.3 ng/min. Each pulse of LH was followed by a rise in the secretion of estradiol-17beta. Maximum secretion of estradiol-17beta was 5.18 +/- 0.72 ng/min and was reached 25 min after LH discharge. Basal secretion of androstenedione was higher than estradiol-17beta at about 1.5 to 3.4 ng/min, and increased to a maximum 26.8 +/- 6.6 ng/min 25 min after LH discharge. Steroid secretion was not maintained at maximum rates and had returned to basal levels 2 h after LH discharge. The data show that the ovary of the anestrous sheep is capable of secreting steroids following pulses of endogenous LH. These results strongly suggest that as in the luteal phase of the cycle, the quantity of estradiol and androstenedione secreted by the ovary is related to the frequency of episodic pulses of LH.