Physiological role of nitric oxide in gallbladder emptying in men

This study was designed to determine the role of nitric oxide in gallbladder (GB) contractions in men. The studies were performed in 10 young healthy male volunteers. GB emptying was examined by ultrasonography under basal conditions and after intravenous infusion of cholecystokinin (CCK8; 12.5 pmol/kg x h) or yolk intake in tests without (saline) and with intravenous infusion of NG-monomethyl-L-arginine (L-NMMA; 4.0 micromol/kg x h) and/or L-arginine (1 mmol/kg x h). The plasma CCK level was determined by radioimmunoassay. It was found that the basal GB volume was about 27 +/- 3 ml, and after CCK8 infusion or yolk meal this volume was reduced within about 30 min by about 93 and 80%, respectively. Pretreatment with L-NMMA caused reduction of the baseline volume by about 15% and significantly augmented the GB emptying induced by CCK8 infusion and yolk intake. L-Arginine alone failed to affect basal or stimulated (CCK or yolk) emptying of the GB, but when combined with L-NMMA, it reversed the enhancement of GB contraction caused by L-NMMA. The basal plasma CCK level was 1.2 +/- 0.3 pmol/l and rose to 7.9 +/- 2.1 pmol/l with CCK8 infusion and to 4.7 +/- 1.8 pmol/l after yolk meal. No significant change in plasma CCK levels was observed in tests with L-NMMA and/or L-arginine. We conclude that under physiological conditions, the GB contractile activity is regulated predominantly by CCK, but endogenous nitric oxide has a tonic relaxing influence on this activity.