Regulation of prostaglandin biosynthesis by nitric oxide is revealed by targeted deletion of inducible nitric-oxide synthase

We investigated the effects of targeted deletion of the inducible NO syntha se (iNOS) gene on the formation of prostaglandins in vivo and ex vivo. Peri toneal macrophages were obtained from control and iNOS-deficient mice, and prostaglandin E-2 (PGE(2)) was quantified after stimulation with gamma-inte rferon and lipopolysaccharide to induce COX-a, Total nitrate and nitrite pr oduction was completely abolished in cells from iNOS-deficient animals comp ared with control cells. PGE, formation by cells from MOS-deficient animals was decreased compared with cells from control animals 80% at 12 h (0.85 /- 0.90 ng/10(6) cells versus 15.4 +/- 2.1 ng/10(6) cells, p < 0.01) and 74 % at 24 h (9.4 +/- 4.3 ng/10(6) cells versus 36.8 +/- 4.1 ng/10(6) cells, p < 0.01), COX-2 protein expression was not significantly different in cells from control or knockout animals. Levels of PGE(2) in the urine of iNOS-de ficient mice were decreased 78% (0.24 +/- 0.14 ng/mg of creatinine versus 1 .09 +/- 0.66 ng/mg of creatinine, p < 0.01) compared with control animals. In addition, the levels of urinary F-2-isoprostanes, an index of endogenous oxidant stress, were significantly decreased in iNOS-deficient animals. In contrast, the levels of thromboxane B-2 derived from platelets allowed to aggregate ex vivo were significantly increased in iNOS-deficient mice compa red with wild-type mice. These studies support the hypothesis that NO and/o r NO-derived species modulate cyclooxygenase activity and eicosanoid produc tion in vivo.