In vitro evidence that vasoactive intestinal peptide is a transmitter of neuro-vasodilation in the head of the cat.

Experiments have been undertaken to determine the nature of the atropine-resistant neurogenic dilation that can be demonstrated in vitro in cephalic arteries of the cat. Levels of vasoactive intestinal peptide (VIP) and substance P were measured in a number of arteries and related to the extent of the neurogenic dilation that can be elicited in vitro. There is no correlation between the tissue contents of the two peptides. A positive correlation was found between vasoactive intestinal peptide but not substance P content and neurogenic dilation. Vasoactive intestinal peptide but not substance P consistently caused a concentration-dependent dilation of cephalic arteries not subject to significant tachyphylaxis. Vasoactive intestinal peptide antiserum in concentrations that block the dilation to vasoactive intestinal peptide (10(-6) M) but not that due to papaverine, significantly reduced neurodilation of both atropinized and non-atropinized lingual arteries--the cephalic artery with the highest VIP content. These results suggest that vasoactive intestinal peptide and not substance P significantly contributes to the non-cholinergic neurogenic dilation observed in vitro in arterial segments from the head of the cat.