Nitric oxide synthesis in myocardium following burn injury in rats

We investigated nitric oxide and cyclic GMP production in myocardium early after burn injury in rats. Nitric oxide synthase activity was measured in cytosol from the left ventricular wall of burned rats. Cytosol from control group animals was shown to contain mainly Ca2+-dependent nitric oxide synthase (cNOS) with a small amount of Ca2+-independent nitric oxide synthase (iNOS). Following burn injury, there was a marked increase in iNOS activity with a peak at 8 h post-burn, however, myocardial cNOS activity was found to decline. Parallel to iNOS induction there was a significant increase in myocardial nitric oxide and cyclic GMP production. All these changes were alleviated by treatment of the rats with dexamethasone. Since increases in cyclic GMP levels in the heart were associated with reduced myocardial contractility, it is possible that enhanced production of nitric oxide by a Ca2+-independent NO synthase accounts, at least in part, for the depression of myocardial contractility seen in burn animals and patients.