Activation of leukocytes with complement C5a is associated with prostanoid-dependent constriction of large arteries in atherosclerotic monkeys in vivo.

Activated leukocytes release a variety of substances which have been shown in vitro to modulate vascular tone. The chemotactic peptide complement C5a is a physiological activator of leukocytes. We injected human recombinant complement C5a (10 and 100 micrograms) into the blood-perfused hind limb of normal and atherosclerotic cynomolgus monkeys and examined vascular responses. In both normal and atherosclerotic monkeys, the high dose of C5a produced about 65% decrease in leukocyte cell count in venous blood drainage from the hind limb. Injection of C5a produced a pronounced increase in resistance of large arteries (segment from iliac artery to dorsal pedal artery) in atherosclerotic, but not in normal monkeys. The constrictor effect of C5a in atherosclerotic monkeys was abolished by the thromboxane A2 receptor antagonist SQ 29,548 (2 mg/kg i.v.). The platelet-activating factor antagonist WEB 2086 (5 mg/kg, i.v.) did not alter vascular responses to C5a. We conclude that activation of leukocytes produces constriction of large arteries in atherosclerotic, but not normal, monkeys in vivo. This response may be mediated in part by release of thromboxane A2.