Effect of Nω-nitro- l-arginine methyl ester on cardiac haemodynamic responses to adenosine infusion in conscious rats

Abstract

1. 1. The aim of the present study was to evaluate the role of NO in the cardiovascular effects of adenosine in conscious rats. 2. 2. Cardiac index was determinated by thermodilution. In a group of rats, three doses of adenosine were infused (i.v.) at a rate of 150, 300 and 450 μg/kg/min in the absence and in the presence of l-NAME (10 mg/kg). In a second group of rats, the experimental protocol was the same as that of the first group, except an infusion of methoxamine (50 μg/kg/min) was given during the second adenosine administration, instead of L-NAME. 3. 3. In the absence of l-NAME or methoxamine, adenosine induced a dose-dependent decrease in mean arterial pressure and an increase in vascular conductance although adenosine did not affect cardiac index. 4. 4. l-NAME administration attenuated the decreasing effect on the mean arterial pressure in response to the two lower doses of adenosine. In the presence of L-NAME, adenosine induced a significant increase in cardiac index 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-induced increase in vascular conductance. 5. 5. Methoxamine infusion induced an enhanced response to adenosine infusion. In the presence of methoxamine, adenosine induced a significant greater decrease in mean arterial pressure, and increase in cardiac index and vascular conductance. 6. 6. These results indicate that part of the cardiovascular effects of adenosine can be mediated by NO, since L-NAME administration partially blocked the adenosine-induced vasodilatation.