Relationship between nitric oxide and prostaglandins in carrageenin pleurisy

The correlation between endogenous nitric oxide (NO) generation and prostaglandin biosynthesis was studied in rat carrageenin pleurisy induced by the injection of 0.2 mL of 1\% lambda-carrageenin into the pleural cavity. The pleural exudate was collected at 4 hr and the amounts of NO2- + NO3- (NOx) and prostaglandin E2 (PGE2) measured. The NOx present in the inflammatory exudate was determined by measuring the NO2- with the Griess reaction, after the reduction of NO3- to NO2- using acid-washed cadmium powder. PGE2 was measured by radioimmunoassay. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 1-3-10 mg/kg subcutaneously) reduced NOx by 20 +/- 7\%, 41 +/- 6\% and 55 +/- 9\% (P < 0.01) and PGE2 by 9 +/- 6\%, 41 +/- 11\% and 74 +/- 9\% (P < 0.001). Conversely, L-arginine (300 mg/kg SC) increasedNOx by 39 +/- 7\% (P < 0.01) and PGE2 by 78 +/- 6\% (P < 0.001). The NO scavenger haemoglobin (Hb), coinjected into the pleural cavity (3 mg/site) with carrageenin, produced a parallel inhibition of NOx (65 +/- 16\%, P < 0.001) and PGE2 (71 +/- 18\%, P < 0.001). The soluble guanylate cyclase inhibitor methylene blue (Mb; 2 mg/site) had no effect. Moreover haemoglobin, but not methylene blue, was able to significantly suppress the L-arginine-induced increase of both NOx and PGE2. In each pleural exudate, independently from the animal treatment, the amount of NOx was highly correlated to the amount of PGE2 (r = 0.93, P < 0.001). These results suggest that in rat carrageenin pleurisy the modulation of the L-arginine:NO pathway results in a parallel modulation of prostaglandin biosynthesis. The interaction between cyclooxygenase and the NO pathway may represent an important mechanism for the modulation of the inflammatory response.