Effects of Cytochrome P-450 Inhibitors on Endothelium-Dependent Relaxation in Rabbit Aorta

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Abstract
Endothelium-dependent relaxation in rabbit aorta was inhibited by exposure to two cytochrome P-450 inhibitors, metyrapone and SKF-525A. Aortic rings were contracted to a stable plateau by addition of phenylephrine (10–7M). Relaxation was elicited by the cumulative addition of methacholine (3 × 10-8–3 × 10–6M) or A23187 (10–8_10–6M). Exposure to metyrapone (500 µM) or SKF-525A (10 µg/ml) was found to inhibit relaxation in response to concentrations of methacholine exceeding 10–7M. Maximal relaxation was inhibited 73% by metyrapone. Relaxation stimulated by concentrations of A23187 exceeding 10–7M was also found to be inhibited by both metyrapone and SKF-525A exposure. Maximum A23187-induced relaxation (55% of the phenylephrine contractile response) was inhibited 40% by metyrapone and 55% by SKF-525A. Arachidonic acid (10–100 µM) also elicited endothelium-dependent relaxation in rings pretreated with indomethacin (10 µg/ml) and contracted with phenylephrine. This relaxation response was abolished by exposure to metyrapone or SKF-525A. These results suggest that cytochrome P-450 may be involved in endothelium-dependent relaxation responses, perhaps by metabolizing arachidonic acid to active products.