EVIDENCE THAT SECRETORY PRODUCTS OF THE RETICULOEPITHELIAL CELLS OF THE RAT THYMUS MODULATE THE SECRETION OF GONADOTROPINS BY RAT PITUITARY-CELLS IN CULTURE

It is now well accepted that the endocrine system can be strongly infl uenced by the immunological status of the body. This laboratory has pr ovided documented evidence that the rat thymus produces a biologically active secretion, with a molecular weight of approximately 30 kDa, th at augments the gonadotrophin-releasing hormone (GnRH) stimulated secr etion of gondotrophins by isolated pituitary cells in culture. To dete rmine the cells of origin of the factor involved, the reticulo-epithel ial cells from the thymus were incubated in vitro to provide media for the examination of possible effects on the secretion of gonadotrophin s by the rat pituitary. The enrichment of the culture with reticulo-ep ithelial cells was confirmed using anti-cytokeratins antibodies. It wa s found that the addition of such conditioned medium increased the sec retion of luteinizing hormone (LH) and follicle stimulating hormone (F SH), with a greater effect on the former. The increment in gonadotroph in secretion was time- and dose-dependent. This same conditioned mediu m also potentiated the effect of GnRH on the cultured pituitary cells. The fractionation of thymic-conditioned medium using selective molecu lar membrane filters, provided evidence that the active factor or fact ors involved in the enhanced secretion of gonadotrophins are larger th an 10 kDa MW. Present findings show that thymic reticulo-epithelial ce lls are responsible for this activity.