Vasoactive intestinal peptide as a neurotransmitter in the cerebral circulation.

Cat cerebral arteries exhibit a non-cholinergic neurogenic vasodilation which is absent in rabbit cerebral arteries. Levels of vasoactive intestinal peptide (VIP) measured by radioimmunoassay are correlated with the presence of a non-cholinergic vasodilation: 270 +/- 66 pmol/g in the cat anterior cerebral artery compared to 10 +/- 2.3 pmol/g in rabbit cerebral arteries. In the absence of endothelial cells, cat cerebral arteries do not relax to acetylcholine, but continue to relax to nerve stimulation. Relaxation responses to VIP also persist. These findings are consistent with the possibility that VIP mediates non-cholinergic vasodilator responses in the cerebral circulation.