Reproductive endocrinology in Hatano high- and low-avoidance rats during the estrous cycle

The high- and low-avoidance animals (HAA and LAA rats) were originally selected from Sprague-Dawley rats for their shuttle-box task. Reproductive endocrinology during the estrous cycle was compared between HAA and LAA rats. All HAA rats showed a regular 4-d estrous cycle, whereas most LAA rats (70.8%) showed a regular 5-d estrous cycle. The peak level of preovulatory luteinizing hormone (LH) surge level was significantly lower in LAA rats than in HAA rats on the day of proestrus. In contrast, the peak level of prolactin surge on the day of proestrus was significantly higher in LAA rats than in HAA rats. Plasma concentrations of follicle-stimulating hormone (FSH) and estradiol-17beta were significantly lower in LAA rats as compared with HAA rats at 12 h on the day of estrus and from 24 h on the day of diestrus to 18 h on the day of proestrus. On the other hand, plasma concentrations of progesterone were significantly higher in LAA rats compared with HAA rats on the day of diestrus. The number of antral follicles (300-600 microm in diameter) at 12 h on the day of proestrus was significantly fewer in LAA rats than in HAA rats. The size and number of corpus luteum at 12 h on the day of estrus were significantly greater in LAA rats than in HAA rats. These results clearly demonstrated that apparent differences are observed in reproductive endocrinology between two Hatano strains. These strain differences probably originated from neural regulation of pituitary hormones.