Isolated bovine cerebral arteries from rostral and caudal regions: distinct responses to adrenoceptor agonists.

Responsiveness to norepinephrine and related agents was compared in isolated bovine anterior cerebral (ACA). middle cerebral (MCA), intracranial internal carotid (ICA), posterior communicating (PCOM), posterior cerebral (PCA) and basilar arteries (BA). Norepinephrine contracted the strips from ACA, MCA and ICA, but relaxed those from PCOM, PCA and BA. In the presence of propranolol, the amine-induced contractions tended to be potentiated in ACA, MCA and ICA, and the relaxations in PCOM, PCA and BA were reversed to contractions. The maximum contractions induced by norepinephrine in ICA and ACA treated with propranolol were significantly greater than those in PCA and BA, but the EC50 values did not differ among arteries. In ACA and MCA, the contractions induced by phenylephrine were greater than those induced by clonidine. The contractions induced by norepinephrine and phenylephrine were attenuated by prazosin but not influenced by yohimbine in ACA and MCA treated with propranolol. These findings indicate that the responses to norepinephrine evidently differ in bovine cerebral arteries of rostral (ACA, MCA and ICA) and caudal regions (PCOM, PCA and BA), possibly due to different functioning of alpha/beta receptors. The amine-induced contraction predominantly seen in the rostral arteries appears to be associated with activation of the alpha 1 adrenoceptor subtype.