ENDOTOXIN SHOCK IN THE PRIMATE: TREATMENT WITH PHENOXYBENZAMINE

Modification, by aspirin and indomethacin, of the haemodynamic and prostaglandin releasing effects of E. coli endotoxin in the dog

1 Dogs treated with aspirin (10 mg/kg) or indomethacin (1.5 mg/kg) 45 min before, and 3 h after, an LD50 dose (1 mg/kg) of E. coli endotoxin were alive 72 h later. 2 Although all dogs in both treated groups survived, only those treated with indomethacin were protected against the fall in blood pressure 1-2 min following endotoxin. 3 Endotoxin increased the level of prostaglandin F2alpha in both the mixed venous and arterial blood. No increase was observed in the aspirin and indomethacin-treated groups. 4 Aspirin and indomethacin treatment did not modify thrombocytopaenia or blood coagulation parameters following endotoxin.

Endotoxin-induced regional circulatory changes in the unanesthetized monkey

Endotoxin in eight unanesthetized monkeys produced a small decrease in cardiac output, a marked fall in blood pressure, and a decrease in total peripheral vascular resistance. The distribution of cardiac output was measured by injecting nuclide-labeled radioactive microspheres (50µ in diameter) into the left ventricle, and blood flow and vascular resistance were calculated for each organ. All vascular beds except that of the spleen reacted with variable degrees of vasodilation, and the most pronounced decreases in resistance were observed in the coronary, gastrointestinal, and adrenal vasculature. Cerebral flow was reduced, but flow was maintained in the brain stem and cerebellum. In contrast to studies in other species, both the gastrointestinal tract and the kidneys showed vasodilation and no significant decrease in flow during the early phase of endotoxemia.

There is some similar evidence in humans of decreased total systemic peripheral resistance without abnormal myocardial function or pooling of blood during the early phase of endotoxemia. The acute regional circulatory changes we have found appear to indicate that endotoxin either directly or through secondary biochemical reactions initiates and maintains a generalized (except for the spleen) vasodilation that reflex compensatory mechanisms cannot overcome. This vasodilation is particularly critical in preventing maintenance of adequate blood flow to the cerebral hemispheres.

Vasodilator Therapy in Acute Hemorrhagic Shock

Results of this study show that 18 of 20 dogs survived prolonged periods of arterial hypotension when phenoxybenzamine was given to maintain adequate flow to the vital tissues of the body. This drug was used in order to block the catecholamine-induced arteriolar vasoconstriction and the histamine-induced venospasm. Reduction of peripheral resistance results in an increased perfusion of the capillary beds and a correction of O 2 and CO 2 tensions at the tissue level. One must emphasize the need for adequate fluid replacement, with this form of therapy; otherwise the marked vasodilation which occurs with phenoxybenzamine might result in an inadequate circulation, even as the resistance to flow in hypoxic tissues is eliminated.