INDUCTION OF CYCLOOXYGENASE-2 IN RAT VASCULAR SMOOTH-MUSCLE CELLS IN-VITRO AND IN-VIVO

Prostaglandins are synthesized from arachidonic acid by the rate limit ing enzyme cyclooxygenase (prostaglandin G/H synthase). Active cycloox ygenase is encoded by two distinct and independently regulated genes, termed cyclooxygenase-1 (cox1) and cyclooxygenase-2 (cox2). In this in vestigation, we examined the expression of cox1 and coxa mRNA in rat a orta following balloon deendothelialization (BDE) in vivo and in rat a ortic smooth muscle cells (SMC) after serum stimulation in vitro. Two h after BDE, rat aortic cox2 mRNA levels increased greater than 50-fol d relative to the lowest detectable levels on days 2 and 14. No messag e was detectable in non-BDE control rat aortas. Similar to the results found in vivo, cultured SMC exhibited a greater than 45-fold increase in cox2 mRNA levels after a 2-h exposure to serum. This increase was transient because cox2 levels declined at 4 and 8 h. In contrast, mini mal changes in cox1 mRNA levels were observed after BDE or serum treat ments. Increased levels of cox2 mRNA and corresponding protein synthes is led to an accumulation of total cyclooxygenase protein, which remai ned elevated 24 h after serum stimulation. Serum-treated SMC also gene rated greater amounts of cyclooxygenase-dependent metabolites than qui escent SMC as evidenced by marked increases in prostaglandin E(2) cont ent in conditioned media, This increase is associated with a 2.5-3.0-f old increased rate of arachidonic acid conversion to prostaglandin E(2 ). Our data indicate that injury and serum stimulation differentially regulate mRNA and protein expression of two distinct cox genes in vasc ular SMC in vivo and in vitro. The findings suggest that the prostanoi d responses after vascular injury are, in part, mediated by acute incr eases in cox2 mRNA and cyclooxygenase-2 protein.