Pattern of ovarian progesterone secretion during the luteal phase of the ovine estrous cycle.

Abstract

Pulsatile secretion of progesterone has been observed during the late luteal phase of the menstrual cycle in the rhesus monkey and human. As the luteal phase progresses in each of these species, there is a pattern of decreased frequency and increased amplitude of progesterone pulses. The present study was designed to determine the pattern of progesterone secretion during the late luteal phase (Days 10-16) of the normal ovine estrous cycle. Five unanesthetized ewes, each bearing an indwelling cannula in the utero-ovarian vein, were bled every 15 min from 0800 h on Day 10 through 0800 h on Day 16 of the estrous cycle. With the computer program PULSAR, it was determined that progesterone secretion was episodic, with pulsations observed on all days. Analysis of variance was used to determine differences in frequency, amplitude, and interpeak interval (IPI) of progesterone pulses among ewes and days. The ewes averaged 8.0 +/- 0.63 pulses of progesterone per 24 h. Mean frequency of pulses was not different between days but showed differences between ewes. Mean amplitude of progesterone pulses was 7.0 +/- 0.27 ng/ml, with no differences observed either between days or between ewes. Mean IPI was 197 +/- 7.1 min, and, like frequency, the IPI was not different between days, but varied between ewes. No consistent temporal relationship was found between progesterone pulses and luteinizing hormone (LH), as determined by bioassay and radioimmunoassay, on Day 14 of the cycle in one ewe. The results indicate that progesterone secretion is episodic during the luteal phase of the ovine estrous cycle and is independent of LH pulses.(ABSTRACT TRUNCATED AT 250 WORDS)