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Studies on the Cerebral Circulation of the Baboon in Acutely Induced Hypertension

The upper limit of autoregulation of cerebral blood flow was investigated in eight young baboons with the intracarotid 133xenon clearance method. Blood pressure was increased by intravenous angiotensin infusion. Autoregulation was effective during blood pressure increase from normotensive levels to a mean pressure of 130 to 139 mm Hg. At this pressure, cerebrovascular resistance reached a maximum. With further blood pressure increase, autoregulation was broken, and the vascular resistance dropped significantly. This flow increase was restricted to the fast component of the 133xenon clearance curve, leaving the slow component unchanged. Blood pressure was kept above the upper limit of autoregulation for 10 to 114 minutes. When the pressure was subsequently decreased, flow values returned to normal in half of the animals, while cerebral hyperemia persisted in the other half. The latter group of animals had been kept above the upper limit of autoregulation for a comparatively longer time, and the persistent hyperemia may have been caused by overstretching of the arteriolar walls. In some animals, angiotensin was infused into the internal carotid artery prior to the autoregulation study in doses not influencing systemic blood pressure. No pharmacological action of angiotensin on CBF was noted.