ENDOTHELIN-STIMULATED MONOCYTE SUPERNATANTS ENHANCE NEUTROPHIL SUPEROXIDE PRODUCTION

Endothelin-1 (ET-1) is a vasoconstrictive peptide released by ischemic /injured endothelium which increases intracellular ionized calcium (Ca 2+]i in vascular smooth muscle. Previous work from this lab has shown that ET-1 also increases human peripheral blood monocyte [Ca2+]i, and that 24 h incubation of monocytes with 10(-9) M ET-1 causes production of prostaglandin E2 and interleukin-6. In these studies, ET-1-stimula ted monocyte supernatants were evaluated for their effect on neutrophi l superoxide production. While ET-1 alone had no direct effect, incuba tion of neutrophils for 20 min in ET-1-stimulated monocyte supernatant s resulted in a 10-fold increase in superoxide production over basal l evels, 44% as much superoxide production as induced by peptide N-formy l-methionyl-leucyl-phenylalanine (N = 6, p < .001). Monocyte supernata nts were analyzed for interleukin-8 (IL-8 or neutrophil activation pro tein) content by radioimmunoassay. ET-1-stimulation resulted in produc tion of 54% as much IL-8 as lipopolysaccharide controls (N = 6, p<.001 ). While a number of monokines can activate neutrophils, IL-8 has been shown to be a potent neutrophil activator as well as a superoxide pri mer. Therefore, ET-1 -treated monocytes probably upregulate neutrophil superoxide production via a mechanism which includes IL-8.