Noradrenaline as a possible mediator in the renal response to vascular expansion with blood in the cat.

In chloralose anaesthetized cats with renal arterial pressure kept constant at 100 mmHg, vascular expansion with precirculated blood, 20 ml kg b.w.-1, caused significant increments in arterial inflow rates of blood to the deep (ARBFD) and superficial (ARBFS) renal venous drainage area of 35 +/- (SE)10 and 19 +/- 6%, respectively, and in the excretion rates of water and sodium of 73 +/- 24 and 75 +/- 28%, respectively, while GFR remained essentially unchanged. In acutely denervated kidneys the responses to expansion were not significantly different from those of innervated kidneys, which indicated largely humoral mediation. Arterial plasma concentrations of noradrenaline, adrenalin, and vasopressin fell significantly to values of a half to one-third of pre-expansion values, while plasma dopamine was not significantly changed by expansion. The response to expansion could be (1) reversed by a 'substituting' intraaortic infusion of noradrenaline, and (2) imitated, without volume expansion, by an infusion of an alpha-adrenergic blocking agent (phentolamine). It is concluded that the renal response (excretory and vascular) to volume expansion with blood is largely humorally mediated and that circulating noradrenaline may play a causal role in the response.