Renin secretion in intact dogs following incubation of epinephrine in blood in vivo

Previous experiments have shown that epinephrine-induced renin secretion in vivo apparently is initiated by activation of extrarenal adrenoceptors. However the location of these receptors has not been determined despite considerable search. The present experiments were designed to evaluate the hypothesis that epinephrine-induced renin secretion is initiated by a change in blood composition, independent of the passage of the blood through any organ. Accordingly, the left kidneys of anesthetized dogs were perfused with femoral arterial blood via an extracorporeal circuit. The circuit consisted of large-bore Tygon tubing (157 ml volume) with an infusion port and a mixing chamber near the femoral arterial origin, and a blood sampling and pressure-monitoring site near the renal artery. A roller pump was used to maintain renal perfusion pressure approximately equal to femoral arterial pressure, and renal blood flow was measured with an electromagnetic flowmeter. Transit time (of a dye) in the extracorporeal circuit was approximately 40 seconds. Intravenous infusion of epinephrine at 25 ng X kg-1 X min-1 increased renin secretion significantly. However, infusion of epinephrine into the extracorporeal circuit at a rate of 5 ng X kg-1 X min-1 did not alter renin secretion, even though epinephrine concentration in the renal perfusate was higher than during intravenous infusion. The data do not support the hypothesis that epinephrine-induced renin secretion is initiated by a direct effect of epinephrine on blood composition, independent of the passage of blood through any organ.