Plasma atrial natriuretic polypeptide and angiotensin II in rats during anesthesia and volume loading

These experiments investigated the effect of halothane or fentanyl anesthesia on plasma atrial natriuretic polypeptide (ANP) and angiotensin II (AII) concentrations and the response to a 30% blood volume load in rats. Halothane (1.1% and 2.2% inspired) or fentanyl (50 and 200 micrograms/kg) anesthesia alone produced little change in basal plasma ANP levels but did increase plasma AII levels above unanesthetized baseline concentrations. A 30% blood volume load in conscious rats produced a transient increase in blood pressure and central venous pressure, a threefold rise in plasma ANP, and a decrease in AII. These effects were not significantly altered by fentanyl anesthesia. In contrast, during 2.2% halothane anesthesia the increase in plasma ANP produced by volume loading was greater and the decrease in AII was abolished. These results indicate that fentanyl does not increase basal ANP levels or markedly change the hormonal response to a volume load. Altered responses seen during deep halothane anesthesia may result from cardiovascular changes or a direct stimulation of physiological mechanisms that release ANP.