Inducible nitric oxide synthase pathway in the central nervous system and vasopressin release during experimental septic shock

Background. Septic shock is characterized by arteriolar vasodilation and hypotension. We have tested the hypothesis that nitric oxide arising from inducible nitric oxide synthase in the central nervous system is responsible for the deficiency in vasopressin release and consequent hypotension during experimental septic shock. Methods and Results: Septic shock was induced In male Wistar rats by intravenous injection of 1.5 mg/kg lipopolysaccharide. After llpopolysaccharide administration, we found a significant decrease in mean arterial pressure with a concomitant increase in heart rate, a significant decrease In diuresis, and a transitory decrease in body temperature. An increase In plasma vasopressin concentrations occurred in these animals and was present for 2 hrs after llpopolysaccharide administration, returning close to basal concentrations thereafter and remaining unchanged for the next 24 hrs. When lipopolysaccharide was combined with central administration of aminoguanidine, an Inducible nitric oxide synthase Inhibitor, we observed a sustained Increase in plasma vasopressin concentration and In the maintenance of blood pressure at 4 and 6 hrs after llpopolysaccharide treatment compared with rats treated with lipopolysaccharide alone. Conclusion: These data indicate that central nitric oxide arising from the inducible nitric oxide synthase pathway plays an important Inhibitory role in vasopressin release during experimental septic shock and may be responsible for the hypotension occurring in this vasodilatory shock.