1. Department of Biochemistry, All India Institute of Medical Sciences, New Delhi–110016, India

Abstract

A POSSIBLE tropic role of pituitary on thymus has been suggested by several studies. Hypophysectomy causes an atrophy of the gland^1–4 and thymus is poorly developed in Snellbagg genetically dwarf mice with hypopituitary function⁵. A diminution of thymus size and a reduction in immunological responses to T cell-dependent antigens is also seen after administration of anti-hypophyseal serum⁶. 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^4,7,8. Thyrotropin, via the thyroid hormones, also exercises a thymotropic action⁹. ACTH, via corticosteroids, causes the transient diminution of the gland¹⁰. 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.