RENAL AUTOREGULATION DURING INFUSION OF NORADRENALINE, ANGIOTENSIN AND ACETYLCHOLINE

To examine whether renal autoregulation was abolished by vasoconstriction and vasodilatation, experiments were performed on anesthetized dogs with intact renal circulation and nervous supply. Angiotensin or noradrenaline was infused into the renal artery at a constant rate that reduced renal blood flow (RBF) to less than half of control values. By mechanical constriction of the renal artery, perfusion pressure could be reduced to averages of 69 and 80 mm Hg respectively (74 mm Hg during control conditions), before RBF dropped more than 5%. Normal autoregulation was also obtained during intravenous infusion of angiotensin and noradrenaline. during stimulation of renal nerves, and after development of tachyphylaxis to angiotensin. At normal and low arterial pressures, but at similar RBF, noradrenaline or angiotensin was injected into the renal artery. RBF was least reduced at low perfusion pressure, indicating that autoregulation did not compensate for the vasoconstrictive effect of noradrenaline and angiotensin. By acetylcholine infusion. RBF could be doubled, and a curvilinear relationship between RBF and perfusion pressure was obtained. Similar curves could be constructed by the application of Poiseuille's law on the premise that vasoactive agents act mainly on muscle elements other than those participating in autoregulation. It is concluded that autoregulation is essentially independent of nervous and humoral stimuli. © 1969 Scandinavian Physiological Society