Effects of PAF and BN 52021 on cardiac function and regional blood flow in conscious rats.

The effect of intravenous injections (0.1-3 nmol/kg) of platelet-activating factor (PAF) on blood pressure, heart rate, cardiac output, and blood flow (hindquarter, renal, mesenteric) were studied in conscious rats. PAF decreased blood pressure and total peripheral resistance (TPR) but increased heart rate; cardiac output was reduced by the highest dose. Low doses of PAF increased blood flow and decreased vascular resistance in all vascular beds, whereas high doses reduced mesenteric blood flow in part by increasing mesenteric vascular resistance. The hypotensive and cardiac effects of PAF were blocked by intravenous infusions of the selective PAF-receptor antagonists, 15 mg/kg BN 52021 and 1 mg/kg SDZ 63-441. BN 52021 also attenuated the hindquarter and renal responses to PAF, but the mesenteric responses remained relatively unchanged. The results indicate that PAF is a potent vasodilator of mesenteric greater than hindquarter = renal vessels at low doses and a cardiac depressant at high doses. A therapeutic role for the PAF antagonists BN 52021 and SDZ 63-441 is suggested in endotoxemia, anaphylaxis, and other disease states in which increased release of PAF contributes to key hemodynamic derangements.