The influence of constitutive Cox-2 in smooth muscle tissue on the contractile effect of phenylephrine in the rat abdominal aorta

Prostanoids are involved in the phenylephrineinduced contraction of the aorta. Here, we examined whether or not constitutive cyclooxygenase-2 (phosholipases C and A2) is the source of prostanoids in the smooth muscle of the arterial wall of the thoracic and abdominal aorta. Both cyclooxygenase isoforms (COX-1 and COX-2) were expressed in the two aortic segments, but their expression was not altered by phenylephrine, the protein synthesis inhibitor cycloheximide, or the phospholipase A₂ inhibitors arachidonyl trifluoromethyl ketone and methyl arachidonyl fluorophosponate. Indomethacin and NS398, which are a non-selective and selective COX-2 inhibitor, respectively, but not SC-560, which is a COX-1-selective inhibitor, inhibited the effect of phenylephrine on the abdominal, but not the thoracic, aorta. Similarly, U73122, which is a phospholipase C inhibitor, and RHC80267, which is a diacylglycerol lipase inhibitor, inhibited the effect of phenylephrine. These findings suggest that prostanoids, which are produced by constitutively active COX-2, influence the contractile response of the abdominal aorta and that the production of arachidonic acid relies on phospholipase C and diacylglycerol lipase. This work was supported by a research grant from the Coordinación General de Posgrado e Investigación del I.P.N. and partially by grant 46217 to PLS from CONACYT.