NG-nitro L-arginine methyl ester: systemic and pulmonary haemodynamics, tissue blood flow and arteriovenous shunting in the pig

The effects of NG-nitro-Lrarginine methyl ester (L-NAME), an inhibitor of the endothelial nitric oxide (NO) biosynthesis, on systemic and pulmonary haemodynamics, and tissue as well as arteriovenous anastomotic blood flows were investigated in the anaesthetized pig, using simultaneous injections of radioactive microspheres of two different sizes (diameter: 15 and 50μm). L-NAME (1, 3 and 10 mg·kg-1) reduced systemic and pulmonary artery conductance and cardiac output, but heart rate and mean arterial blood pressure remained unchanged. L-arginine reversed the systemic and pulmonary haemodynamic changes induced by L-NAME. As detected with 15 μm microspheres, L-NAME (1 and 3 mg·kg-1) decreased tissue blood flow to and vascular conductance in the eyes, lungs, atria, kidneys, adrenals and liver. Furthermore, the difference between blood flows simultaneously measured with 15 and 50 μm microspheres, which can be equated to blood flow through arteriovenous anastomoses with a diameter between about 28 and 90 μm, was reduced by L-NAME (3 mg · kg-1) in the skin of head and gluteal regions and, as indicated by the microsphere content of the lungs, in the total systemic circulation. These results suggest that in the anaesthetized pig (i) NO is involved in the regulation of both systemic and pulmonary vascular conductance, (ii) the decrease in systemic vascular conductance is in part due to constriction of systemic arteriovenous anastomoses, and (iii) the decrease in pulmonary vascular conductance, leading to reduction of cardiac output, seems to negate the expected rise in arterial blood pressure observed, for example, in rats and rabbits following inhibition of NO-synthesis