Effects of metabolic inhibitors on endothelium‐dependent and endothelium‐independent vasodilatation of rat and rabbit aorta

1. Basal release of endothelium-derived relaxing factor (EDRF) rendered endothelium-containing rings of rat aorta 4.7 fold less sensitive to the contractile actions of phenylephrine and depressed the maximum response when compared with endothelium-denuded rings. The responsiveness and maximum response to phenylephrine was, however, similar in rings of rabbit aorta with or without endothelium. 2. Rotenone (1 nM-0.1 microM), an inhibitor of oxidative phosphorylation, induced a profound, irreversible blockade of phenylephrine-induced tone in endothelium-containing and endothelium-denuded rings of rat aorta, but induced only slight inhibition of tone in rings of rabbit aorta. 3. 2-Deoxy glucose (10 mM), an inhibitor of glycolysis, had no effect on phenylephrine-induced contraction in endothelium-denuded rings of rat aorta, but inhibited reversibly the endothelium-dependent depression of contraction in endothelium containing rings. 2-Deoxy glucose had no effect on phenylephrine-induced contraction in rings of rabbit aorta with or without endothelium. 4. Rotenone (0.1 microM) inhibited acetylcholine-induced, endothelium-dependent relaxation of phenylephrine-contracted rings or rat and rabbit aorta. In endothelium-denuded rings of rat aorta, relaxation induced by glyceryl trinitrate of isoprenaline was also inhibited, but relaxation induced by 8-bromo cyclic GMP or dibutyryl cyclic AMP was not. Relaxation induced by verapamil on KCl-contracted, endothelium-denuded rings of rat aorta was also unaffected. 5. 2-Deoxy glucose (10 mM) inhibited acetylcholine-induced, endothelium-dependent relaxation of phenylephrine-contracted rings of rat and rabbit aorta. In endothelium-denuded rings of rat aorta, relaxation induced by glyceryl trinitrate and by isoprenaline was also inhibited, but relaxation induced by 8-bromo cyclic GMP or dibutyryl cyclic AMP was not. Relaxation induced by verapamil on KCIcontracted, endothelium-denuded rings of rat aorta was also unaffected. 6. These data suggest that in rabbit and in rat aorta, rotenone inhibits acetylcholine-induced relaxation by inhibiting EDRF production, and by depressing smooth muscle sensitivity to EDRF, respectively. They further suggest that 2-deoxy glucose inhibits acetylcholine-induced relaxation in both tissues by depressing the sensitivity to EDRF, probably as a result of reduced synthesis of cyclic GMP. The additional possibility that 2-deoxy glucose inhibits EDRF production warrants further investigation. 7. The blockade by 2-deoxy glucose of the endothelium-dependent depression of phenylephrine-induced tone in rat aorta probably reflects blockade of the actions of spontaneously released EDRF.