Molecular and pharmacological approaches to inhibiting nitric oxide after burn trauma

Whereas controversial, several studies have suggested that nitric oxide (NO) alters cardiac contractility via cGMP, peroxynitrite, or poly(ADP ribose) synthetase (PARS) activation. This study determined whether burn-related upregulation of myocardial inducible NO synthase (iNOS) and NO generation contributes to burn-mediated cardiac contractile dysfunction. Mice homozygous null for the iNOS gene (iNOS knockouts) were obtained from Jackson Laboratory. iNOS knockouts (KO) as well as wild-type mice were given a cutaneous burn over 40% of the total body surface area by the application of brass probes (1 × 2 × 0.3 cm) heated to 100°C to the animals' sides and back for 5 s (iNOS/KO burn and wild-type burn). Additional groups of iNOS KO and wild-type mice served as appropriate sham burn groups (iNOS/KO sham and wild-type sham). Cardiac function was assessed 24 h postburn by perfusing hearts (n = 7-10 mice/group). Burn trauma in wild-type mice impaired cardiac function as indicated by the lower left ventricular pressure (LVP, 67 ± 2 mmHg) compared with that measured in wild-type shams (94 ± 2 mmHg, P < 0.001), a lower rate of LVP rise (+dP/dt_max, 1,620 ± 94 vs. 2, 240 ± 58 mmHg/s, P < 0.001), and a lower rate of LVP fall (-dP/dt_max, 1,200 ± 84 vs. 1,800 ± 42 mmHg/s, P < 0.001). Ventricular function curves confirmed significant contractile dysfunction after burn trauma in wild-type mice. Burn trauma in iNOS KO mice produced fewer cardiac derangements compared with those observed in wild-type burns (LVP: 78 ± 5 mmHg; +dP/dt: 1,889 ± 160 mmHg/s; -dP/dt: 1, 480 ± 154 mmHg/s). The use of a pharmacological approach to inhibit iNOS (aminoguanidine, given ip) in additional wild-type shams and burns confirmed the iNOS KO data. Whereas the absence of iNOS attenuated burn-mediated cardiac contractile dysfunction, these experiments did not determine the contribution of cardiac-derived NO versus NO generated by immune cells. However, our data indicate a role for NO in cardiac dysfunction after major trauma.