Role of Oxidative Metabolism on Endothelium-dependent Vascular Relaxation of Isolated Vessels

The obligatory role of endothelium in mediating vasodilator response to numerous humoral agents has been definitely accepted. However, the chemical identity of endothelium-derived relaxing factor(s) (EDRF) and the mechanisms underlying its synthesis and release remain unclear. Much evidence suggests a compartmentalization of ATP into cells, such that ATP derived from glycolysis or from oxidative metabolism is used for different cellular functions. To investigate which energy source (i.e. oxidativevglycolytic metabolism) is preferentially used for the biosynthesis and/or release of EDRF, rings of rabbit thoracic aorta were studied in organ chambers. After preconstriction with PGF2α, inhibition of glycolysis with either iodoacetate (300μ ) (n=6) or 2-deoxyglucose (20 m ) (n=6) did not affect concentration–response curve to the endothelium-dependent agent acetylcholine. In contrast, inhibition of oxidative metabolism with either 1 m amytal or 5μ rotenone markedly impaired relaxation to acetylcholine. In fact, maximal relaxation was 75±5% in control rings (n=6), and 42±7% (P<0.01) in amytal-treated rings (n=6), whereas rotenone converted acetylcholine relaxation into constriction (n=6;P<0.001). The effect of amytal on endothelium-dependent relaxation was reversible, suggesting that endothelial cells were not damaged by the inhibitor. Amytal also markedly reduced endothelium-mediated relaxation to ADP (37±6%;P<0.05;n=5), as well as to the calcium ionophore A23187. Neither mitochondrial inhibitor affected relaxation to nitroglycerin, an endothelium-independent agent. Finally, amytal did not affect relaxation to S-nitrosocysteine (a recently proposed EDRF) (n=5), suggesting that the effects on acetylcholine and ADP responses were not due to non-specific interferences with EDRF once released from endothelial cells. In conclusion, our data demonstrate that the active process of biosynthesis and/or release of EDRF requires energy derived mainly from mitochondrial oxidative metabolism.