Studies on the involvement of endogenous neuropeptides in the control of thymocyte proliferation in the rat

The possible involvement of endogenous vasoactive intestinal peptide (VIP), cholecystokinin (CCK) and neurotensin (NT) in the control of thymocyte pro liferation has been investigated in vivo in the immature rat. For this task , we have studied the effects of the administration of selective antagonist s of the receptors of the three neuropeptides on the mitotic index (parts p er thousand of metaphase-arrested cells after vincristin injection) of thym ocytes. Both CCK- and TN-receptor antagonists were ineffective. In contrast , two VIP receptor antagonists (VIP-As) enhanced the mitotic index of thymo cytes. VIP reversed the effect of VIP-As, but when administered alone it di d not alter the mitotic activity of thymocytes. In light of these findings, we conclude that endogenous VIP exerts a maximal tonic inhibitory influenc e on the basal proliferative activity of rat thymocytes, while endogenous C CK and NT do not play a relevant modulatory role in this process.