Effects of capsaicin on the contractility and peptide-containing nerves of large cerebral arteries of the cat.

Capsaicin caused a vasoconstrictor response of the cat middle cerebral and basilar arteries in vitro both in the presence and absence of active tone. The vasoconstrictor response to capsaicin appeared and attained almost the maximum level at a dose of 10(-7) M. It is likely that capsaicin directly induced a contraction of smooth muscle cells, since the vasoconstrictor response was independent of the presence of endothelium and nerve components. When the tissue exhibited an active tone by the application of uridin 5'-triphosphate, the contractile response was evoked by capsaicin at lower concentrations. The maximum developed tension was greater in denervated tissues than in control tissues. After the exposure of the tissue to capsaicin in vitro, the intensity of substance P- and CGRP-like immunofluorescence diminished markedly, while that of neuropeptide Y- and vasoactive intestinal polypeptide-like immunofluorescence was not grossly altered. These results indicate that, while capsaicin releases and depletes some vasodilator peptides from perivascular nerves, the powerful direct vasoconstrictor effect overwhelms the vasodilator effects in large cerebral arteries of cats.