RENAL VASCULAR EFFECTS OF EPINEPHRINE INFUSION IN THE HALOTHANE-ANESTHETIZED PIGLET

The objective of this study was to determine the dose-response effects of epinephrine, given by systemic intravenous infusion to the halotha ne-anesthetized newborn piglet, on renal blood flow, mean arterial blo od pressure, and renal vascular resistance. Seven newborn piglets were acutely instrumented. A transit-time ultrasound flow probe was placed around the renal artery and a femoral arterial catheter was placed fo r blood pressure monitoring. Epinephrine was infused in doubling doses from 0.2 to 3.2 mu g . kg(-1) . min(-1). Mean arterial blood pressure increased from 54 mmHg (1 mmHg = 133.3 Pa) to an average of 96 mmHg a t 3.2 mu g . kg(-1) . min(-1) of epinephrine. Renal blood flow increas ed from 165 mL . min(-1) . 100 g(-1) at baseline to 185 mL . min(-1) 1 00 g(-1) at a dose of 0.2 mu g . kg(-1) . min(-1) and increased furthe r at 0.4 and 0.8 pg . kg(-1) . min(-1) to reach 261 mL . min(-1) . 100 g(-1). Renal blood flow began to fall at a dose of 3.2 mu g . kg(-1) . min(-1), remaining however, significantly above baseline (211 mt . m in(-1) . 100 g(-1)). Consequently, calculated renal vascular resistanc e fell as the dose was increased from 0.2 to 0.8 mu g . kg(-1) . min(- 1) and then rose again at 1.6 and 3.2 mu g . kg(-1) . min(-1), being s ignificantly above baseline at 3.2 mu g . kg(-1) . min(-1). These resu lts demonstrate that epinephrine when given by systemic infusion to th e halothane-anesthetized newborn pig is a renal vasodilator at low dos es and causes renal vasoconstriction at moderate to high doses. Renal blood flow remained above baseline at all doses tested, and thus, with in the dosage range tested, epinephrine infusion should not cause rena l ischemia.