Role of nitric oxide in local blood flow control in the anaesthetized dog

Intravenous infusion of NG-nitro-L-arginine methyl ester (L-NAME), a potent inhibitor of nitric oxide (NO) formation from L-arginine, provokes marked rises in arterial blood pressure by increasing peripheral resistance. In order to further evaluate the contribution of basal NO-formation to control of organ blood flow, regional blood flow distribution within the myocardium, kidney and brain areas was assessed using the tracer-microsphere technique in anaesthetized dogs. After L-NAME (20 mg kg-1 i.v.) kidney perfusion was homogeneously reduced by 55% in the entire cortex and the outer medulla. Within the left ventricular myocardium regional blood flow significantly decreased only in subepicardial layers (-12%), whereas within the entire right ventricle regional blood flow was reduced by 19-24%. A close inverse relationship was found between all changes in regional myocardial blood flows observed after L-NAME and the respective control values. No significant changes in regional blood flow in different areas of the brain were detectable after L-NAME. It is concluded that the contribution of basal NO formation varies greatly between different organs and exhibits significant regional differences within the heart. It is possible that local metabolic mechanisms may compensate functionally for the inhibition of NO synthesis.