An anterior pituitary factor stimulates thymidine incorporation in isolated thymocytes

A possible tropic role of pituitary on thymus has been suggested by several studies. Hypophysectomy causes an atrophy of the gland and thymus is poorly developed in Snellbagg genetically dwarf mice with hypopituitary function. A diminution of thymus size and a reduction in immunological responses to T cell-dependent antigens is also seen after administration of anti-hypophyseal serum. The pituitary may contain several active principles affecting directly or indirectly the thymus functions. Of these, growth hormone has been shown to have a promoting effect on metabolic activities of the thymus and on immune responses involving the participation of thymus-derived T cells. Thyrotropin, via the thyroid hormones, also exercises a thymotropic action. ACTH, via corticosteroids, causes the transient diminution of the gland. We report here the presence in pituitaries of a previously unknown small molecular weight peptide(s) which stimulates markedly the incorporation of tritiated thymidine into DNA in isolated thymocytes