Influence of norepinephrine and angiotensin II on vasomotion of renal blood supply in humans.

Oscillatory behavior of smooth muscle, including arterial smooth muscle, has been identified in many preparations. In this study we have extended observations on vasomotion of the renal blood supply in humans by assessing the response to norepinephrine or angiotensin II infused directly into the renal artery in doses sufficient to reduce renal blood flow by 25-33% but not influence blood pressure. In placebo-treated patients, renal blood flow and the indexes of vasomotion determined by an estimation of power spectral density of xenon transit through the human kidney did not change. Norepinephrine induced a striking increase in the amplitude but not the cycle length of oscillatory activity, whereas angiotensin (despite a somewhat larger reduction in renal blood flow) induced only a modest change in amplitude. The phasic response to norepinephrine infused continuously makes it unnecessary to invoke phasic norepinephrine release in the response to maneuvers that increase sympathetic nervous system activity. Moreover, oscillatory activity reflects phenomena that may be related to but are not dependent on changes in mean renal blood flow. The results of this study may provide insight into the pathogenesis of the increase in vasomotion evident in the renal blood supply of some patients with essential hypertension.