Emergences of LH surge affected by different progesterone levels in ovariectomized goats

The purpose of the present study was to determine the priming effects of progesterone that affect the emergence of LH surge mode secretion by three different progesterone levels. In previous studies, we have shown that LH surge occurred in follicular levels of progesterone, whereas there was no surge mode secretion of LH and FSH in either the subluteal or luteal levels of progesterone. In this study, the hypothesis was that the priming effects of progesterone on the timing of the LH surge induced by exogenous estradiol are same between subluteal and luteal levels of progesterone. Long-term ovariectomized Shiba goats that had received implants of estradiol capsules (Day 0) and three different progesterone silastic packet inducing follicular, subluteal and luteal levels of progesterone were divided into three groups such as non-P, low-P and high-P group. Blood samples were collected daily throughout the experiment for the analysis of gonadal steroid hormone levels. On Day 7, all devices of progesterone packets were removed but estradiol capsules were maintained during the experiment, and blood samples were collected at 1 hr interval for 12 h from the time of progesterone removals to determine peripheral changes of estradiol and progesterone concentration. Then all animals were infused estradiol on the Day 7 after 13 h from the removals of progesterone devices with a peristaltic pump into jugular vein at a rate of 3 μg/h for 36 h. For analysis of peripheral LH and estradiol concentration, blood samples were collected via another jugular vein at 2 h intervals for 52 h (from 4 h before the start of estradiol infusion to 48 h after the start of estradiol infusion). In all animals of the three groups treated with estradiol infusion, an LH surge was expressed but the peak time of LH surge was different. This time interval from estradiol infusion until the peak of LH surge was gradually and significantly extended by the different levels of progesterone treated before estradiol infusions in the three groups.