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Figure 6 (Left) Effects of nitroglycerin (NTG) treatment on (14C)-PGH2–dependent prostanoid production in rabbit aortas. Results are expressed as the mean value ± SEM from five experiments. *p < 0.05 vs. control by analysis of variance. Solid bars = without NTG treatment; open bars = with NTG treatment. (Right) Schematic diagram depicting the effects of NTG-induced formation of peroxynitrite (ONOO–) on arachidonic acid metabolism. ONOO– inhibits the conversion of the cyclooxygenase product PGH2 (prostacyclin endoperoxide) by the prostacyclin synthase via tyrosine nitration. This effect can be mimicked in vitro by using the prostacyclin synthase inhibitor U51605. The remaining PGH2 will act directly or indirectly (via formation of thromboxane A2 [TXA2]) on the thromboxane receptor (TxR), leading to enhanced constriction.
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