Time course of plasma and pulmonary lymph endothelin-like immunoreactivity during sustained endotoxaemia in chronically instrumented sheep

1. Endothelin, a novel vasoconstrictor 21-residue peptide isolated from the supernatant of cultured porcine endothelial cells, has been shown to be increased in plasma in a variety of cardiovascular disease states, including acute myocardial infarction, acute renal failure and essential hypertension. We determined the time course of plasma and pulmonary lymph endothelin-like immunoreactivity in relation to the progressive deterioration of cardiopulmonary function in an ovine septic shock model leading to multi-organ failure syndrome and death within 42 h of a continuous intravenous infusion of Escherichia coli endotoxin (40 ng min−1 kg−1). 2. Plasma and pulmonary lymph endothelin-like immunoreactivity were measured by r.i.a. using a specific antiserum raised in rabbits against porcine endothelin-1. Endothelin-like immunoreactivity was further determined in lung tissue and the thoracic duct lymph of endotoxin-treated sheep by reversed-phase h.p.l.c. In control instrumented conscious sheep not infused with endotoxin, there were no significant changes in any of the measured cardiopulmonary and biochemical variables, with plasma and pulmonary lymph endothelin-like immunoreactivity remaining below the detection limit (< 1 pg/tube) throughout the 72 h study period. 3. Conscious sheep receiving endotoxin showed a major hypotensive septic syndrome, including persistently decreased systemic blood pressure, systemic vascular resistance, stroke volume, left ventricular stroke work, associated with sustained pulmonary vasoconstriction and protein-rich pulmonary oedema (> five-fold increase in pulmonary lymph flow and protein clearance), and marked lactic acidosis, leading to the death of animals within 14–42 h despite institution of mechanical ventilation and adequate intravascular volume replacement. 4. Appearance of endothelin-like immunoreactivity, as revealed by r.i.a., in arterial plasma and pulmonary lymph was simultaneous in both circulatory beds, with peak values measured between 4 and 12 h after the start of endotoxin infusion (plasma: 68 ± 8 pg/ml, pulmonary lymph: 88 ± 18 pg/ml, P < 0.05 compared with control sheep). After 12 h of endotoxaemia, endothelin-like immunoreactivity in both fluids progressively decreased up to the death of the animals, although remaining significantly above that measured in control sheep. The analysis of extracts of lung and thoracic duct by reversed-phase h.p.l.c. revealed that the r.i.a. method used in the present study mainly detected endothelin-1. 5. Our results demonstrate the presence of a marked and persistent increase in endothelin-like immunoreactivity in plasma and pulmonary lymph of sheep during lethal endotoxin shock with multi-organ failure, suggesting a continuous production and/or release of endothelin-1 into the pulmonary lymph and the systemic circulation upon continuous endotoxin infusion. These findings suggest that endothelin may contribute to the vasomotor disturbances observed during the development of septic shock, although studies using selective receptor antagonists or synthesis inhibitors are required to definitively confirm a potential pathophysiological role of endothelin during endotoxaemia.