Thymosin- 4 Concentrations during the Estrous Cycle and after Hypophyseal Stalk Transection of Female Pigs

Abstract

Thymosin-beta 4 (ThB4) concentrations in the peripheral circulation of pigs were investigated during the first 30 days after weaning and after hypophyseal stalk transection of ovariectomized females. Significant increases in ThB4 were observed during the day of weaning, during follicular development, and during early luteal formation. During the first period of follicular development (Days 1 to 5 after weaning), ThB4 was uniformly elevated for 3 days whereas during the second period of follicular development (days 21 to 25 after weaning), the increase in ThB4 was bimodal. This period of bimodal secretion was closely associated with luteolysis. ThB4 concentrations were low during the luteal phase when progesterone concentrations were at their greatest. In ovariectomized pigs, ThB4 concentrations were not influenced acutely by a single intravenous injection (2 micrograms) of luteinizing hormone-releasing hormone in control (hypophyseal stalk intact) or hypophyseal stalk transected females. Both of these treatment groups responded to luteinizing hormone-releasing hormone with increased secretion of luteinizing hormone. These studies determined that ThB4 secretion changed dramatically throughout the estrous cycle of pigs but failed to identify an acute association between increased luteinizing hormone secretion and ThB4 in ovariectomized pigs. Our observations support the hypothesis that the thymus gland interacts with the hypothalamopituitary-ovarian axis primarily through changes in secretion of ovarian steroids.