CARDIOVASCULAR EFFECTS OF N-G-METHYL-L-ARGININE IN CHRONICALLY INSTRUMENTED CONSCIOUS DOGS

The cardiovascular effects of nitric oxide blockade were examined in f ive conscious chronically instrumented dogs. The hypothesis tested was that nitric oxide release plays a role in vascular tone and regional organ blood flow under physiological conditions. Aortic pressures; the first derivative of the left ventricular pressure; cardiac output (CO ); heart rate; and carotid, coronary, renal, hepatic, and portal blood flows were recorded before and after bolus injection of 5, 10, and 20 mg/kg of N-G-methyl-L-arginine (L-NMA). In response to L-NMA, mean ar terial pressure increased by 7, 20, and 35%, respectively, in a dose-d ependent manner, whereas CO decreased. CO reduction was sustained at t he highest dose, whereas peripheral blood flows were not altered. Thes e data suggest that blocking basal nitric oxide synthesis by administe ring L-NMA leads to a modest dose-dependent presser response despite a marked and sustained reduction in CO recorded at the highest dose of L-NMA. Moreover, within our dose range, although the nitric oxide synt hase inhibition provides a significant presser response, it does not a lter the resting carotid, coronary, renal, hepatic, and portal blood f lows.