Haemodynamic and haematologic effects of Acanthaster planci venom in dogs

This study was designed to examine haemodynamic and haematologic effects of the crown-of-thorns starfish venom (Acanthaster planci venom: APV) in dogs. Severe systemic hypotension, thrombocytopenia and leukopenia were induced by APV (1.0 mg protein/kg i.v.), followed by gradual return to the baseline level within 60 min. Hypotension was presumably caused by two factors: an early decrease in systemic vascular resistance and the large reduction in cardiac output due to reduced ventricular filling. Indomethacin, a cyclooxygenase inhibitor, remarkably suppressed systemic hypotension induced by APV. The peak reduction in systemic pressure was associated with concomitant rise of plasma 6-keto-PGF1 alpha, a major stable metabolite of prostacyclin. Thus, the hypotensive effect of APV may be caused primarily by prostacyclin and/or some vasodilating prostaglandins. In contrast, thrombocytopenia and leukopenia were not affected by cyclooxygenase inhibitor, 5-lipoxygenase inhibitor or platelet activating factor (PAF) receptor antagonist. When APV was administered repeatedly, tachyphylaxis was developed in haemodynamic effects, but not in haematologic effects. These findings suggest that APV-induced hypotensive effects may occur mainly through endogenous production of vasodilating prostaglandins including prostacyclin, although APV-induced thrombocytopenia and leukopenia may be caused by other mechanism(s) unrelated to arachidonate metabolites and/or PAF.