Nitric oxide and the haemodynamic profile of endotoxin shock in the conscious mouse

1. The release of cytokines following administration of endotoxin and the contribution of nitric oxide (NO) to the subsequent haemodynamic profile were investigated in the conscious mouse.
2. Administration of endotoxin (E. Coli, 026 : B6, 12.5 mg kg⁻¹, i.v.) elevated the concentration of tumour necrosis factor-α (TNF-α) in the plasma within 0.5 h, reaching a maximum at 2 h and returning to control concentrations by 4 h. In addition, the concentration of interleukin-6 (IL-6) in the plasma was also elevated within 1 h, reaching a maximum at 3 h and remaining elevated throughout the 12 h of study.
3. Endotoxin (12.5 mg kg⁻¹, i.v.) induced the expression of a Ca²⁺-independent (inducible) NO synthase in the mouse heart and elevated the concentrations of nitrite and nitrate in the plasma within 4 h, reaching a maximum at 12 h. This was accompanied by a progressive fall in blood pressure over the same period.
4. The vasopressor effect of noradrenaline (0.5–4 μg kg⁻¹ min⁻¹, i.v.) administered as a continuous infusion was significantly attenuated 7 h after endotoxin (12.5 mg kg⁻¹, i.v).
5. The NO synthase inhibitor N^G-monomethyl-L-arginine HCl (L-NMMA; 1–10 mg kg⁻¹, i.v. bolus) reversed the fall in blood pressure when administered 7 h after endotoxin (12.5 mg kg⁻¹, i.v.).
6. In an attempt to maintain a constant blood concentration, L-NMMA was administered as a continuous infusion (10 mg kg⁻¹ h⁻¹, i.v.), beginning 4 h after a lower dose of endotoxin (6 mg kg⁻¹, i.v.). Such treatment prevented the fall in blood pressure and the elevation of nitrite and nitrate in the plasma throughout the 18 h of observation.
7. The fall in blood pressure following endotoxin (3 mg kg⁻¹, i.v.) was significantly reduced throughout the 18 h of observation in homozygous mutant mice lacking the inducible NO synthase.
8. In summary, we have developed a model of endotoxin shock in the conscious mouse in which an overproduction of NO by the inducible NO synthase is associated with the haemodynamic disturbances. This model, which exhibits many of the characteristics of septic shock in man, will enable the study of the pathology of this condition in more detail and aid the investigation of potential therapeutic agents both as prophylactics and, more importantly, as treatments.