Substance P: immunohistochemical localization and effect upon cat pial arteries in vitro and in situ.

Abstract

1. Nerve fibres containing substance P immunoreactivity were present in the adventitia and the adventitia‐media border of all cat cerebral arteries which were examined. Substance P immunoreactivity was most abundant in cerebral arteries from the rostral portion of the circle of Willis. 2. Substance P effected a dose‐dependent relaxation of feline middle cerebral arteries which had been contracted with prostaglandin F2 alpha. The maximum relaxation (16 +/‐ 0.3 mN) was achieved with substance P at a concentration of 10‐6 M. 3. In cats anaesthetized with alpha‐chloralose, the perivascular microinjection of substance P effected dose‐dependent increases in arteriolar calibre. The maximum increase in calibre (19 +/‐ 3%) was observed following the injection of 10(‐6) M‐substance P.