The role of nitric oxide (NO) mechanisms in control of pyloric function and transpyloric flow were investigated in six conscious dogs. Antropyloroduodenal motility, transpyloric flow, and gastric emptying were measured 15 min after intravenous injection of 100 ml of either saline, L-arginine (50 mg/kg), L-NNA (5 mg/kg), or L-arginine (50 mg/kg) followed by L-NNA (5 mg/kg). Infusion of L-NNA was associated with retardation of gastric emptying (65 +/- 6%) in the first 30 min, in comparison to the saline (90 +/- 3%) or L-arginine (90 +/- 2%). This effect was prevented by infusion of L-arginine prior to L-NNA, after which 89 +/- 3% of the liquid emptied in 30 min. There was a significant reduction (P < 0.05) in the number and volume of flow pulses, and an increase in pyloric tone (P < 0.05) after L-NNA in comparison to the other three test conditions. There were no differences, however, in the number of antropyloric or isolated pyloric pressure waves under the four conditions. Our findings suggest that NO mechanisms influence gastric emptying and transpyloric flow of nonnutrient liquids by altering the pyloric tone, thus increasing resistance to flow.