Adrenergic vasoconstrictor activity in the cerebral circulation after inhibition of nitric oxide synthesis in conscious goats

The interaction between nitric oxide (NO) and adrenergic activity in the cerebral circulation was studied using conscious goats, where blood flow to one brain hemisphere (cerebral blood flow) was electromagnetically measured, and the effects of phentolamine and hexamethonium on cerebrovascular resistance were evaluated before (control) and after inhibition of NO synthesis with N W-nitro- l-arginine methyl ester ( l-NAME). l-NAME (12 goats, 40 mg kg −1 administered i.v.) reduced cerebral blood flow from 62±3 to 44±2 ml min −1, increased mean systemic arterial pressure from 100±3 to 126±4 mm Hg, decreased heart rate from 79±5 to 50±4 beats min −1, and increased cerebrovascular resistance from 1.63±0.08 to 2.91±0.016 mm Hg ml −1 min −1 (all P