Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 17, 1999
Publication Date: N/A
Interpretive Summary: The testis and thymus make chemicals called hormones that affect reproduction, growth and health of animals. An understanding of how the testis is regulated and how it interacts with target organs will ultimately lead to improved domestic animal production. Studies were conducted to determine effects of thymic hormone thymulin on testis steroid production. Thymulin synergized with gonadotropins (LH) in stimulating increases in androgen production but had no effect on estrogen production in vitro. Increases in androgen synthesis in vivo from thymulin injection were related to the levels of endogenous gonadotropins. Regulatory aspects of thymic function extend beyond the general health of animals and may have important roles in maintaining gonadal function and reproductive capability. Such information indicates thymic hormones play an important role in health and reproduction, and understanding regulation may improve animal production.
Technical Abstract: Numerous immuno-peptides have now been shown to have positive or negative effects on steroidogenic function of the gonads, but few have been tested outside of rodent species. In vitro incubation of thymulin (a nine-amino acid secretory peptide of the thymus; 1, 10, 100, and 1000 ng/ml) and thymulin with hCG were tested in Chinese Meishan boars of high gonadotropin/testicular steroidogenic function and White composite boars o European origin. In White composite boar testis, thymulin stimulated testosterone during the early periods of incubation (1-3 h; p < 0.05) and depressed testosterone concentrations at later times (6-12 h; p < 0.05). Thymulin had no effect on androgen synthesis in testis from Meishan boar testis but stimulated estrone synthesis. Thymulin synergized with hCG in stimulating increases in testosterone and dehydroepiandrosterone/ dehydroepiandrosterone sulfate in White composite boars (primarily 1- and 3-h incubation periods; p < 0.05) but had no effect in Meishan testicular incubates. In vivo effects of thymulin were further tested in three genetic lines of boars selected for high, medium, or low circulating concentrations of LH (Meishan, Select White composites, and control White composites, respectively). Injection of thymulin (4.4, 44.4, and 444.4 ng/kg BW) into cannulated (jugular) boars generally resulted in a decrease followed by a later (2-3 h) increase in circulating testosterone concentrations (p < 0.01) proportional to the boar's general circulating LH concentrations. Overall results from these studies indicate a thymulin augmentation of LH stimulation of androgen synthesis.