Changes in thymosin β4 and gonadal function during puberty in boars and gilts immunized against estrone

Abstract

Thymosin β4, a thymic secretory peptide, may have an important integrative role in gonadal function by promoting the release of gonadotrophin releasing hormone (GnRH). To investigate possible thymic endocrine relationships to gonadal function in swine, serum changes in thymosin β4 were monitored throughout the prepubertal period in gilts and boars immunized against either keyhole limpet hemocyanin (KLH-controls; gilts 68, boars 6) or KLH conjugated to estrone (anti-E1; gilts 76, boars 6). Immunization was initiated at 5 weeks of age and animals were blood sampled at 4-wk intervals until puberty. Gilts were bred at the second estrus. At 30 ( n = 61) and 70 days ( n = 83) of pregnancy, ovarian weight, corpora lutea weight and numbers, and fetal numbers were collected. At 24 weeks of age, boars were killed and the weights of testes and accessory glands collected. As boars and gilts matured, serum concentrations of thymosin β4 decreased ( P < 0.05) with age. Gilts that attained puberty (estrus) had lower concentrations of thymosin β4( P < 0.05) than animals that demonstrated no estrous activity. No differences were detected between controls or anti-E1 gilts in relation to any reproductive parameters monitored, gonadal steroids or thymosin β4 concentrations. Anti-E1 boars had lower thymosin β4 ( P < 0.05) throughout the prepubertal period than controls, and tended to have lower testicular, epididymal, and prostate weights; only seminal vesicle weight was significantly decreased (103.2 ± 21.2 vs. 173.2 ± 15.2 g, P < 0.05). Boars immunized against estrone tended to have lower Leydig cell numbers ( P < 0.09) and seminiferous tubule diameter ( P < 0.09), but increased Leydig cell size ( P < 0.01). A sexually dimorphic response was noted to immunization against estrone, in that thymosin β4 concentrations were decreased in boars, but unchanged in gilts.