Contribution of platelet activating factor to hemodynamic and sympathetic responses to bacterial endotoxin in conscious rats.

The effect of the platelet activating factor (PAF) antagonist WEB 2086 on blood pressure; heart rate; and plasma glucose, lactate, and catecholamine concentrations were examined following either PAF or endotoxin administration in conscious rats. PAF infusion (50 ng/kg/min for 60 min) resulted in a sustained hypotension, with tachycardia and elevated plasma norepinephrine (NE; 1.8-fold increase), epinephrine (E; 6.7-fold increase), and dopamine (DA; 1.0-fold increase) at 30 min after beginning infusion. Plasma NE, E, and DA became 4.1 (NE)-, 17.4 (E)-, and 3.3 (DA)-fold higher than control at 60 min after beginning infusion. Both the hemodynamic and plasma catecholamine alterations induced with PAF were completely blocked with WEB 2086 pretreatment. Bacterial endotoxin treatment (5 mg/kg, i.v. bolus) produced well-characterized responses of hypotension, tachycardia, hyperglycemia, hyperlactacidemia, and an elevation in plasma catecholamines. Whereas complete blockade of the hypotensive and tachycardic effect of endotoxin was achieved with WEB 2086 at 30 min following endotoxin, the increases in plasma catecholamines and lactate elicited by endotoxin were attenuated but remained significantly higher than control levels. Hyperglycemia following endotoxin was not altered by WEB 2086 treatment. In endotoxic rats pretreated with WEB 2086 there was significant hypotension, tachycardia, and hyperlactacidemia and an elevation in plasma catecholamines at both 60 and 120 min, but all were less severe compared to non-WEB 2086-treated endotoxic animals. The results demonstrate that WEB 2086 completely blocked early endotoxin-induced hypotension and tachycardia but not catecholamine elevation following endotoxin. This work suggests that sympathetic activation following endotoxin may be mediated by factors other than hypotension.