We have shown that bilateral atrial appendectomy attenuates the increase in atrial natriuretic factor and sodium excretion that occurs after acute blood volume expansion. These findings suggest that the atrial appendages influence renal sodium excretion. The purpose of the present study was to determine whether atrial appendectomy alters the increase in sodium excretion that occurs postprandially. One to two weeks after surgery, conscious monkeys (Macaca fascicularis) were given a meal through a nasogastric tube. The meal consisted of water (20 ml/kg), sodium (2.5 mmol/kg), carbohydrate (2.65 g/kg), protein (0.68 g/kg), and fat (0.89 g/kg). Postprandial changes in renal function were monitored for 210 min after the meal was started. In the sham animals, urine flow increased from 0.23 +/- 0.04 to 0.55 +/- 0.05 ml/min, sodium excretion increased from 28.6 +/- 7.8 to 84.4 +/- 12.3 mumol/min and fractional sodium excretion increased from 1.35 +/- 0.38% to 3.06 +/- 0.43%. Bilateral atrial appendectomy (ATX) significantly attenuated the renal responses to the meal. Urine flow in the ATX animals increased from 0.19 +/- 0.03 to 0.30 +/- 0.02 ml/min, sodium excretion increased from 26.5 +/- 5.8 to 45.8 +/- 15.2 mumol/min, and fractional sodium excretion increased from 0.99 +/- 0.02% to 1.53 +/- 0.34%. Postprandial changes in renal and systemic hemodynamics were also monitored and were similar in both groups. Plasma levels of atrial natriuretic factor were also similar in both groups and did not increase postprandially. These findings demonstrate that bilateral atrial appendectomy attenuates postprandial-induced increases in sodium excretion by mechanisms that do not involve an increase in atrial natriuretic factor.