HETEROGENEOUS RESPONSES OF CANINE BASILAR AND MIDDLE CEREBRAL-ARTERIES TO SEROTONIN AT NORMAL AND HIGH CO2 TENSION

The responses of basilar arteries (BAs) to serotonin were attenuated by high P(CO2) (86 +/- 1 mm Hg) and the pH matched acidotic solution (P(CO2) 37 +/- 1 mm Hg), whereas the responses of middle cerebral arteries (MCAs) were not. High P(CO2) decreased the basal tone of both arteries, and the changes in basal tone due to high P(CO2) were not influenced by 3 x 10(-7) M imipramine, 10(-5) M pargyline or 10(-4) M aspirin. The responses of BAs to serotonin were attenuated by high P(CO2) in the presence of imipramine, pargyline and aspirin. The responses of MCAs to serotonin were not influenced by high P(CO2) in the presence of pargyline and aspirin, but attenuated by high P(CO2) in the presence of imipramine.