Nonuniformity of CBF response to NE- or ANG II-induced hypertension in rabbits

The regional response of brain vasculature to moderate hypertension was investigated using two hypertensive drugs, norepinephrine (NE) and angiotensin II (ANG II), infused intravenously at low concentrations (increase in blood pressure 15-40 mm Hg). Regional cerebral blood flow (rCBF) was measured in unanesthetized and anesthetized rabbits using the [14C]ethanol saturation technique. In both groups of animals, NE and ANG II induced regional differences in the flow changes as compared with controls, confirming a regional (or segmental) heterogeneity in the regulatory mechanisms to hypertension. The responses to identical rises in blood pressure (BP) in most of the structures analyzed depended on the drug used. In the unanesthetized rabbits, the increase in vascular resistance induced by NE was greater than that induced by ANG II. With the two drugs, there was no correlation between the flow changes in any of the structures considered and either the BP increase or the BP level in unanesthetized animals. However, these flow changes were correlated with the BP increase in anesthetized animals, although differences between the effects of NE and ANG II were again observed. This study suggests that cerebrovascular regulatory mechanisms in hypertension are probably more complex than a simple myogenic reaction. Their heterogeneity and their dependence both on the cause of hypertension and on the presence of anesthetics suggest the intervention of an integrating pathway.