Heterogeneity in the response to vasoconstrictors of isolated dog proximal and distal middle cerebral arteries.

Responses to vasoconstrictor agents were compared in helical strips of proximal and distal middle cerebral arteries isolated from the same dogs. Contractions induced by 30 mM K+ per cross-sectional areas in the large and small artery strips did not differ significantly so that contractions induced by the agents could be compared relative to those induced by K+. The contractions induced by serotonin were greater in the proximal than in the distal arteries. Histamine produced a greater contraction in the proximal arteries under resting conditions. Distal arteries partially precontracted with prostaglandin F2 alpha responded to histamine with relaxations. The histamine-induced contraction was attenuated by chlorpheniramine, whereas the relaxation was suppressed by cimetidine. Prostaglandin F2 alpha or carbocyclic thromboxane A2 produced similar magnitudes of contractions in the proximal and distal arteries. Thrombin contracted the distal arteries to a greater extent. Contractions induced by norepinephrine or bradykinin did not differ in the proximal and distal arteries. It may be concluded that the ratio of histaminergic H1 and H2 receptor functions decreases peripherally along middle cerebral arteries, whereas the contractile response to bradykinin was not influenced in these arteries of a relatively short distance. The functions of receptor sites for serotonin and thrombin appear to be quite different in large and small cerebral arteries of such a short distance, but alpha-adrenoceptor functions seem to be identical.