Release of vasoactive intestinal peptide in the central nervous system in man.

Recent work has shown that vasoactive intestinal peptide (VIP), one of the many candidate hormones of the gut, also occurs widely in neurones. To determine whether the neuronal peptide may have a neurotransmitter function, we studied changes in immunoreactive VIP in dog plasma and human cerebrospinal fluid after the infusion of choline esterase inhibitors (neostigmine and physostigmine, respectively). Immunoreactive VIP was released in both situations. The systemic changes (in VIP levels) were enhanced five weeks after portacaval shunting in dogs. Our results demonstrate that the immunoreactive VIP level increases as a result of choline esterase inhibitors. The plasma "release" may originate either from peripheral peptidinergic nerve terminals or from APUD cells of the gastroenteropancreatic system. The increase in immunoreactive cerebrospinal fluid VIP may very well originate from central neurons, since the peptide does not apparently cross the blood-brain barrier.