S-Methylisothiourea sulfate improves renal, but not hepatic dysfunction in canine endotoxic shock model

Objective. Excess production of nitric oxide (NO) by inducible NO synthase (iNOS) has been implicated in the pathophysiology of septic shock. This study was designed to see whether S-methylisothiourea sulfate (SMT), a selective inhibitor for iNOS, prevents cardiovascular changes and multiple organ damage in the canine endotoxic shock model. Design: Prospective, comparable experimental study. Setting: Laboratory at a university hospital. Subjects: Twenty male mongrel dogs were studied under pentobarbital anesthesia. Interventions: Dogs were divided into three groups: bacterial lipopolysaccharide (LPS) group (n = 7) receiving continuous infusion of LPS (2 mg/kg/h for 1 h); LPS plus SMT group (n = 7) receiving LPS and SMT (1 mg/kg,bolus i.v., followed by continuous infusion of 1 mg/kg/h for 1 h); and vehicle-plus SMT group (n = 6). Measurements ann results: Hemodynamics, blood gas parameters, and urine output were measured during 6 h observation periods. Serum levels of lactate, transaminases, and bilirubin were measured at baseline, 1 and 6 h. Creatinine and free water clearance, urine sodium excretion and fractional excretion of sodium were calculated. LPS caused a profound hypotension associated with decreases in cardiac output and oxygen delivery, lactic acidosis, renal and liver dysfunction, and thrombocytopenia. SMT prevented the LPS-induced hypotension and renal dysfunction, whereas it did not affect the LPS-induced decreases in cardiac output or oxygen delivery, hyperlactatemia, liver dysfunction, or thrombocytopenia. SMT alone had no appreciable effects on hemodynamics, blood gases, liver or renal functions. Conclusions: These findings show that SMT improves renal, but not hepatic dysfunction, in dogs with endotoxic shock, suggesting that iNOS-derived NO plays differential roles in sepsis-associated multiple organ dysfunction.