Pharmacological characterization of postjunctional α‐adrenoceptors in cerebral arteries from the sheep

1. The responsiveness to noradrenaline was characterized in cerebral arteries from the sheep, since this species was large enough to permit a comparison of arteries from different parts of the cerebral vasculature. 2. Noradrenaline caused contraction of the basilar artery, middle cerebral artery and small pial arteries by stimulation of alpha 1-adrenoceptors. 3. The maximum contraction to noradrenaline was small in the basilar artery (28% of the 5-hydroxytryptamine (5-HT) maximum) but larger in the middle cerebral artery (78% of the 5-HT maximum) and pial artery (92% of the 5-HT maximum) of the sheep. 4. Cocaine (10 microM) potentiated noradrenaline-induced contractions in the sheep middle cerebral artery but not in the sheep basilar artery. 5. The noradrenaline contraction, relative to the 5-HT contraction, was not affected by removal of the endothelium in either the sheep basilar or middle cerebral artery. 6. The results showed a variation within the sheep cerebral vasculature in the response to noradrenaline which cannot be explained by regional differences in alpha-adrenoceptor subtypes, noradrenaline uptake mechanisms or endothelial function.