Effect of NG-monomethyl-L-arginine on regional vascular resistance in rats

This study investigated the effects of intravenous injection of the specific inhibitor of nitric oxide (NO) formation, NG-monomethyl-L-arginine (L-NMMA), on mean arterial pressure and regional vascular resistance in rats (n = 7). Regional vascular resistances of brain, heart, left kidney, intestine (jejunum), left testis and right testis were measured using radiolabelled microspheres before and after injection of 12.5 mg/kg of L-NMMA. Injection of L-NMMA raised mean arterial pressure significantly (p < 0.05) from 119 +/- 4 (mean +/- SEM) mmHg to 139 +/- 7 mmHg, accompanied by a significant (p < 0.05) decrease in both heart rate and cardiac index and an increase in total peripheral resistance. Regional vascular resistances in brain, heart, kidney and intestine increased significantly (p < 0.05) with L-NMMA, but no change was observed in the testes. The results indicate that the resistance of vascular beds is affected by NO synthesis, while the extent of regulation may differ among the various vascular beds.