1 We investigated the effects of the selective endothelin (ET)(A) receptor antagonist BQ-485 and the selective ET(B) receptor antagonist BQ-788 on circulatory failure, multiple organ dysfunction syndrome (MODS) and the alterations in acid base balance caused by endotoxaemia in the anaesthetized rat. 2 Male Wistar rats were anaesthetized (thiopentone sodium; 120 mg kg(-1), i.p.) and received a continuous infusion of vehicle (saline, 0.6 ml kg(-1) h(-1) i.v.), BQ-485 (10 nmol kg(-1) min(-1), i.v.) or BQ-788 (10 nmol kg(-1) min(-1), i.v.). Fifteen min later, animals received a bolus injection of either saline (0.9% NaCl, 1 ml kg(-1), i.v.) or E. coli lipopolysaccharide (LPS, 10 mg kg(-1), i.v.). 3 Injection of LPS resulted in a fall in blood pressure from 115 +/-4 mmHg (time 0) to 82 +/- 4 mmHg at 360 min (n = 15) as well as a hyporeactivity to the presser responses to noradrenaline (NA, 1 mu g kg(-1), i.v.). Infusion of BQ-788 attenuated the delayed hypotension (at 360 min: 100 +/- 4 mmHg, n = 7; P < 0.05) and significantly enhanced the presser responses elicited by NA (at 60 to 240 min). In contrast, treatment of LPS-rats with BQ-485 augmented the hypotension (at 360 min), but did not affect the vascular hyporeactivity elicited by endotoxaemia. 4 Endotoxaemia for 360 min resulted in rises in the serum levels of urea and creatinine (indicators of renal failure), glutamate-oxalate-transferase (GOT) and glutamate-pyruvate-transferase (GPT) (indicators of hepatocellular injury), and bilirubin and gamma-glutamyl transferase (gamma GT) (indicators of liver failure) as well as nitrite (indicator of the induction of nitric oxide synthase; iNOS). Treatment of LPS-rats with BQ-788, but not with BQ-485, attenuated the degree of liver injury and failure, while neither BQ-788 nor BQ-485 affected the acute renal failure or the induction of iNOS caused by endotoxin. 5 Endotoxaemia also caused (within 15 min) an acute metabolic acidosis (falls in pH, HCO3- and base excess) which was compensated by hyperventilation (fall in Paco(2)). Treatment of LPS-rats with BQ-788 or BQ-485 did not affect the metabolic acidosis caused by LPS. 6 Thus, the selective ET(B) receptor antagonist BQ-788 attenuated (i) the delayed hypotension, (ii) the vascular hyporeactivity to NA as well as (iii) the degree df hepatocellular injury and dysfunction caused by endotoxin in the anaesthetized rat. In contrast, the selective ET(A) receptor antagonist did neither attenuate the circulatory failure nor the liver or renal dysfunction associated with endotoxaemia. We propose that the prevention of the hepatocellular dysfunction and injury caused BQ-788 in endotoxaemia is due to an improvement in oxygen delivery to the liver secondary to (i) inhibition of pre-sinusoidal constriction, (ii) inhibition of sinusoidal constriction, and (iii) improvement in perfusion pressure.
