EFFECT OF N-OMEGA-NITRO-1-ARGININE METHYL-ESTER ON CARDIAC HEMODYNAMIC-RESPONSES TO ADENOSINE INFUSION IN CONSCIOUS RATS

1. The aim of the present study was to evaluate the role of NO in the cardiovascular effects of adenosine in conscious rats. 2. Cardiac inde x was determinated by thermodilution. In a group of rats, three doses of adenosine were infused (i.v.) al a rate of 150, 300 and 450 mu g/kg /min in the absence and in the presence of L-NAME (10 mg/kg). In a sec ond group of rats, the experimental protocol was the same as that of t he first group, except an infusion of methoxamine (50 mu g/kg/min) was given during the second adenosine administration, instead of L-NAME. 3. In the absence of L-NAME or methoxamine, adenosine induced a dose-d ependent decrease in mean arterial pressure and an increase in vascula r conductance although adenosine did not affect cardiac index. 4. L-NA ME administration attenuated the decreasing effect on the mean arteria l pressure in response to the two lower doses of adenosine. In the pre sence of L-NAME, adenosine induced a significant increase in cardiac i ndex from 18.7 +/- 1.5 to 29.1 +/- 1.9 and 26.2 +/- 1.4 ml/min/100 g. Administration of L-NAME significantly attenuated the adenosine-induce d increase in vascular conductance. 5. Methoxamine infusion induced an enhanced response to adenosine infusion. In the presence of methoxami ne, adenosine induced a significant greater decrease in mean arterial pressure, and increase in cardiac index and vascular conductance. 6. T hese results indicate that part of the cardiovascular effects of adeno sine can be mediated by NO, since L-NAME administration partially bloc ked the adenosine-induced vasodilatation.