Possible dual role for vasoactive intestinal peptide as gastrointestinal hormone and neurotransmitter substance.

Vasoactive intestinal peptide (V.I.P.) has been found in high concentrations both in the gastrointestinal tract and, unexpectedly, in the central nervous system. Immunocytochemical studies have demonstrated V.I.P. in nerve-fibers. These findings challenge the concept of V.I.P. as a simple gastrointestinal hormone and suggest a possible neurotransmitter function.