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GASTROINTESTINAL, HEPATIC, PULMONARY, AND RENAL

Cyclooxygenase (COX)-1 and COX-2 Participate in 5,6-Epoxyeicosatrienoic Acid-Induced Contraction of Rabbit Intralobar Pulmonary Arteries

Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri

Epoxyeicosatrienoic acids (EETs) have been reported to contract intralobar pulmonary arteries (PA) of the rabbit in a cyclooxygenase (COX)-dependent manner. In the present study, we observed that COX-1 and COX-2 isoforms were expressed in freshly isolated PA of healthy rabbits. We examined the hypothesis that both COX isoforms participate in 5,6-EET-induced contraction of rabbit intralobar PA. Selective inhibition of COX-1 with 300 nM 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC-560) prevented 5,6-EET (1 x 10^–8–1 x 10^–5 M)-induced contractions of isolated intralobar rabbit PA rings in a manner similar to that observed with the nonselective cyclooxygenase inhibitor indomethacin at 10 µM. Selective inhibition of COX-2 with either 100 nM 5-bromo-2-(4-fluorophenyl)-3-(4-methylsulfonyl) thiophene (DUP-697) or 3 µM N-(2-cyclohexyloxy-4-nitrophenyl) methanesulfonamide (NS-398) shifted the EC₅₀ value of 5,6-EET-induced PA contraction to the right but with considerably lower efficacy than SC-560. In rabbit PA, 5,6-EET-induced contraction was primarily dependent on COX-1 activity. Differential metabolism of 5,6-EET by COX-1 and COX-2 does not explain the primary dependence of PA contraction on COX-1 activity because 5,6-EET was metabolized similarly by both COX isoforms. COX-1 and -2 were expressed primarily in PA endothelium where COX-1 expression was dense and uniform, whereas COX-2 expression was sparse and nonuniform. 5,6-EET-induced PA contraction was endothelium-dependent. These results suggest that 5,6-EET-induced contraction is primarily dependent on COX-1 activity.

Address correspondence to: Dr. Alan H. Stephenson, Department of Pharmacological and Physiological Science, 1402 S. Grand Blvd., St. Louis, MO 63104. E-mail: stephens{at}slu.edu

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