Effects of the thymic peptide thymulin on in vitro and in vivo testicular steroid concentrations in white composite and Meishan boars.

Abstract

Immuno-peptides may have positive or negative effects on gonadal steroidogenesis, but few have been tested outside of rodent species or in vivo. In Exp. 1, thymulin, a secreted nonapeptide of the thymus, was incubated (1, 10, 100, or 1,000 ng/mL) with testicular minces (sampled at 3, 6, or 12 h) from Chinese Meishan boars of high gonadotropin/testicular steroidogenic function (n = 8) and White composite boars of European origin (n = 8 ) to test the hypothesis that thymulin could augment hCG stimulation of testicular androgen concentrations. Thymulin alone had few effects on androgen concentrations (testosterone, dehydroepiandrosterone+dehydroepiandrosterone sulfate [DHEA+DHEASO4]) in Meishan boar testicular incubates. In minces from White composites incubated with thymulin, testosterone concentrations were generally below control values (P<.05), but DHEA+DHEASO4 concentrations were unaffected. Thymulin had no effect on estrone concentrations in testicular incubates of White composite boars but stimulated estrone concentrations in Meishan testicular incubates. Thymulin plus hCG increased testosterone (3 and 6 h of incubation; P<.05) but not DHEA+DHEASO4 concentrations in White composite testicular incubates. Thymulin plus hCG did not alter androgen or estrogen concentrations from control values in Meishan testicular incubates. In Exp.2 with a protocol similar to that of Exp. 1 for testicular minces from White composite boars (n = 30), thymulin increased testosterone concentrations during the early incubation period (1 to 3 h; P<.05) and depressed testosterone concentrations at later times (6 h; P<.05). Thymulin synergized with hCG in stimulating increases in testosterone and DHEA+DHEASO4 concentrations (P<.05) but had no effect on estrone concentrations in vitro. Thymulin was tested in vivo in boars from three genetic lines selected for high, medium, or normal circulating LH concentrations (Meishan, select White composites, and control White composites, respectively). Injection of thymulin i.v. (4.4, 44.4, or 444.4 ng/kg BW) generally increased circulating testosterone concentrations (2 to 3 h later; P<.01), but the response was dependent on the boar's general circulating LH concentrations and dose of thymulin. Overall results from these studies support the hypothesis of a thymulin augmentation of LH stimulation of androgen increases in vitro and in vivo in the testis of boars.

Effects of GnRH immunization on the reproductive axis and thymulin

“…Other studies suggested that thymulin stimulates luteinizing hormone (LH) and follicle stimulating hormone (FSH) release from perfused rat pituitaries (Brown et al 2000, Hinojosa et al 2004. Moreover, thymulin could augment LH-mediated stimulation of androgen increases in vitro and in vivo in boar testis (Wise & Ford 1999). These results suggested that thymulin plays a relevant physiological role in the HPG axis.…”

The Immunoendocrine Thymus as a Pacemaker of Lifespan

“…Also studied in suspension of rat pituitary anterior lobes, thymulin had a dual role in the release of gonadotropins, which was dependent on the hormonal status of the donor's pituitary [38]. In combination with gonadotropin stimulation, thymulin increases testicular steroidogenesis [39,40]. Thymosin exercises influences on the secretion of beta endorphin, ACTH, LHRH, LH, and glucocorticoids [41,42].…”

Endocrine disorders and fertility and pregnancy: An update

“…A positive correlation was demonstrated between the concentration of thymulin and LH, as well as a reduction in testosterone production with a decrease in thymulin concentration ( 152 , 153 ). The presence of regulatory T cells within the testes has also been demonstrated ( 154 , 172 ), which, through the secretion of IL-10, affect the ratio of the Th1 to Th2 subpopulation.…”