The release of luteinizing hormone from pituitaries perifused with thymic extracts

Medium obtained by the perifusion of fragments of adult male CSE rat thymuses stimulates the release of luteinizing hormone (LH) from the anterior pituitary gland in vitro. The release of the stimulatory factor/s from the thymus appears to be stimulated by the depolarizing concentration of K+ and to be Ca++-dependent. Perifusates from heart, liver and spleen did not elicit the response suggesting that the effect is specific to the thymus gland. Neither LH nor its releasing hormone, LHRH, were detectable in the thymus perifusates by RIA. Levels of facteur thymique serique (FTS), as measured by bioassay are highest in K+ stimulated fractions that exhibit the greatest LH releasing activity. In separate experiments in vitro FTS, but not two other thymic peptides, thymopoietin and thymosin alpha 1, caused a dose-related release of LH from pituitary tissue. That ability of thymic perifusates to cause the release of LH was age-related because tissue from neonatal and ageing males failed to release compounds with any significant effect on the pituitary release of LH. However, when the thymus was enlarged in ageing rats as a result of orchidectomy 1 month before sacrifice LH release was similar to that observed in young male adults.