[The action of somatotropin and a nonpeptide mitogenic factor on thymocyte proliferative activity]

Hydrocortisone-resistant thymocyte proliferation is stimulated by the nonpeptide mitogenic factor. In vivo incubation of hydrocortisone-resistant thymocytes in the presence of the nonpeptide mitogenic factor results in accumulation of extra- and intracellular hypoxanthine, originating from 8-14C-adenylic acid. Stimulation of in vitro incorporation of 2-14C-thymidine in the thymocyte DNA may be effected via the somatotropic hormone in case nonseparated thymocytes (but not hydrocortisone-resistant ones) are used. No hypoxanthine accumulation in somatotropin-stimulated nonseparated rat thymocytes was observed. 2-14C-thymidine incorporation in the hydrocortisone-resistant thymocyte DNA was enhanced by incubation of the cells in the presence of hypoxanthine in concentrations observed after thymocyte stimulation with nonpeptide mitogenic factor. The authors come to a conclusion that somatotropin and nonpeptide mitogenic factor stimulate the proliferation of two different thymocyte populations, that may be involved in the process of proliferation and regeneration of the thymus exposed to steroids.