Characterization of thymosin alpha 1 and beta 4 during the bovine estrual period: effects of elevated estradiol and progestin.

At present, there is a renewed interest in thymic function and its secretions in relation to endocrine control and reproductive function. In an initial experiment, 60 crossbred heifers (18-20 mo) were detected in estrus and assigned to control or FSH superovulatory groups. On Days 7-14 of the subsequent estrous cycle, FSH was administered for 5 days and prostaglandin F2 alpha (PGF2 alpha) was administered at 48 and 60 h after the initial FSH injection. Control animals received only PGF2 alpha injections between Days 9 and 15 of the cycle. Blood samples were collected from all animals at the time of PGF2 alpha injection and every 12 h thereafter to 72 h post PGF2 alpha injection. In a subsequent experiment, 103 crossbred heifers (16-18 mo) were superovulated with FSH and synchronized to estrus with PGF2 alpha administered 60 h after the initial FSH injection. Twenty-eight of the heifers received Norgestomet implants 12 h prior to the initial PGF2 alpha injection to inhibit the LH surge. Blood samples were collected from animals at 12-h intervals until the PGF2 alpha injection and every 6 h thereafter until 108 h post PGF2 alpha treatment. Although thymosin beta 4 concentrations did change over the estrual period, no differences were noted between control and superovulatory animals in the initial experiment even though estradiol concentrations were increased tenfold from the FSH stimulated ovary. In the second experiment, thymosin beta 4 and alpha 1 increased as the estrual period progressed and decreased (p less than 0.05) subsequent to the LH surge. (ABSTRACT TRUNCATED AT 250 WORDS)