Relationship Between LH, FSH, and Prolactin Concentration and the Secretion of Androgens and Estrogens by the Preovulatory Follicle in the Ewe

Abstract

The ovarian secretion of estradiol, androstenedione, testosterone, and progesterone and the concentration of LH, FSH, and prolactin were measured in the periovulatory period of five ewes with ovarian or utero-ovarian autotransplants. Samples of jugular and ovarian venous blood were collected every 1 or 2 h before and for 96 h after induction of luteal regression on Day 10 of the cycle by injection of 100 µg cloprostenol. Progesterone concentration in jugular vein plasma fell to less than 1 ng/ml in all ewes by 24 h, and coincidental to this decline there was a significant increase in the secretion of LH and prolactin and an associated rise in the ovarian venous concentration of estradiol, testosterone, and androstenedione. The rise in LH secretion was associated with a twofold increase in the frequency of episodic pulses each of which stimulated an increase in the secretion of estradiol. In contrast the concentration of FSH declined significantly in the 48 h after luteal regression. Shortly after the onset of estrus (48 ± 2.5 h), there was a marked rise in the concentration of prolactin, FSH, and LH which reached a peak at 61 ± 4 h. At the start of this preovulating LH surge, there was a further substantial stimulation in the secretion of estradiol, testosterone, and androstenedione, followed by a sharp fall within 3, 5, and 7 h, respectively.