Substance P is markedly increased in plasma of patients with hepatic coma.

Substance P (determined as immunoreactive substance P [i-SP]), noradrenaline, and adrenaline were measured in plasma of 18 patients with hepatic coma (stage I-IV), 16 healthy controls, and 10 critically ill patients without evidence of hepatocellular disease. Plasma i-SP (119 +/- 13 fmol/ml) was significantly higher in patients with hepatic coma than in healthy controls (13 +/- 2 fmol/ml) or control patients (23 +/- 4 fmol/ml). Plasma i-SP rose in parallel with plasma noradrenaline and adrenaline. There was a significant direct correlation between plasma i-SP and noradrenaline. Increase in plasma i-SP and noradrenaline was associated with a decrease in systemic vascular resistance and an increase in cardiac index and was most pronounced in those patients who finally died in coma. Deterioration in the dying patients was accompanied by a further significant increase in plasma i-SP. Immunoreactivity was identified as authentic SP by high performance liquid chromatography in 3 representative patients. Accumulation of the vasodilating peptide SP in plasma of patients with hepatic coma may be important in the pathogenesis of the cardiovascular disturbances associated with this disease.