The reflex effects of renal afferents on the heart were studied in pentobarbital-anesthetized rats (400-425 g) using 2-[14C]deoxyglucose (DG). Three groups of rats were given a single bolus injection of DG (100 mu Ci/kg) 1) six controls, 2) four with periodic electrical stimulation of the proximal end of a cut renal nerve (2 Hz, 0.5-ms width) and 1-mA current, and 3) six with intermittent renal venous occlusion (unilateral). Forty-five minutes after injection the heart was removed, cooled quickly, and frozen-sectioned. Sections 20 micron thick were exposed to film for 12 days. The resulting autoradiographs were scanned using a computerized densitometer, and these densities were converted to relative glucose utilization (GlU, mumol X 100 g-1 X min-1) using the lumped constant for rat brain. Both renal venous occlusion and renal afferent nerve stimulation resulted in a decrease in blood pressure of 6.7 +/- 0.6 mmHg (P less than 0.001) and 7.3 +/- 0.7 mmHg (P less than 0.001) and heart rate-blood pressure product of 5.6 +/- 0.7% (P less than 0.001) and 8.8 +/- 0.8% (P less than 0.001), respectively, and afferent renal nerve stimulation induced a decrease in heart rate of 7.2 +/- 0.9 beats/min (P less than 0.01). However, when compared with control, renal venous occlusion induced a significant increase in GlU in left ventricular myocardium (LV myo, P less than 0.05), endocardium (LV endo, P less than 0.001), and papillary muscle (LV pap, P less than 0.001), whereas afferent renal nerve stimulation induced a significant increase in GlU in LV endo (P less than 0.05) and LV pap (P less than 0.002) only. This study shows both a reflex increase in GlU for the rat heart and a decrease in heart rate with either renal vein occlusion or afferent renal nerve stimulation.