Pulsatile secretion of ovarian progesterone during the luteal phase in ewes

Pulsatile secretion of progesterone (P) has been observed during the late luteal phase of the cycle in the rat, cow, rhesus monkey and human. As the luteal phase progressed in each of these species, there was a pattern of P secretion and to what extent do P pulses correlate with LH pulses during the normal luteal phase (days 10-16) of the ewe. Five unanesthetized ewes, each bearing an indwelling cannula in the uteroovarian vein, were bled every 15 min from 0800 hours on day 10 through 0800 hours on day 16 of the estrous cycle. Using the computer program Pulsar, it was determined that P 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 P pulses among ewes and days. The ewes averaged 8.0 ± 0.7 pulses of P per 24 hours. Mean frequency of pulses was not different among days

0.05) but showed differences among ewes <P < 0.05). Mean amplitude of P pulses was 7.0 ±0.1 ng/ml and also showed no differences among days

0.05), but varied among ewes <P < 0.05). Mean IPI was 197 ± 7.56 min. The IPI was not different between days

0.05), but varied among ewes (P < 0.05). No consistent temporal relationship between P pulses and LH bioassay nor LH immunoassay emerged. The results indicate that P secretion is pulsatile during the luteal phase of the ovine estrous cycle and independent of LH pulses. However, a pattern of decreasing frequency and increasing amplitude of P pulses was not observed in ewes. (Supported by NSF grant DCB 8502702).