Comparison of endothelium‐dependent responses of monkey cerebral and temporal arteries

1 Endothelium‐dependency of vasodilator responses was compared in helical strips of monkey cerebral and superficial temporal arteries contracted with prostaglandin F 2α . Acetylcholine produced an endothelium‐dependent relaxation in the temporal arteries, but did not consistently alter the tone of cerebral arteries. 2 Adenosine 5′‐triphosphate (ATP) produced a transient contraction followed by a relaxation in the temporal and cerebral arteries; removal of the endothelium partially attenuated the relaxation of the cerebral arteries and markedly suppressed the relaxation in the temporal arteries. The dependency of adenosine 5′‐diphosphate (ADP)‐induced relaxations on the endothelium was also greater in temporal arteries than in cerebral arteries. 3 Histamine‐induced relaxations in the temporal arteries were independent of the endothelium and were reversed to contractions by cimetidine. Cerebral arterial relaxations induced by histamine were partly dependent on the endothelium. Relaxations caused by substance P were reversed to contractions by removal of the endothelium in the temporal arteries, whereas the peptide did not consistently alter the tone of cerebral arteries. 4 The Ca 2+ ionophore, A23187, relaxed the temporal and cerebral arteries to a similar extent; removal of the endothelium abolished these relaxations. Glyceryl trinitrate elicited similar relaxations of cerebral and temporal arteries, and these were independent of the endothelium. 5 These findings clearly indicate heterogeneity in the endothelium‐dependency of several vasodilator responses in monkey intra‐ and extracranial arteries, although the ability of these arteries to respond to A23187 and glyceryl trinitrate does not appear to differ. The heterogeneous responses observed so far could therefore be due to different distributions of receptors or to variation in receptor‐effector coupling in endothelial cells.