We exposed isolated rat cardiac myocytes to 20 min of hypoxia followed by 20 min of reoxygenation and observed the effect of supernatants of stimulated neutrophils [polymorphonuclear leukocytes (PMNs)] given at the beginning of reoxygenation. PMN supernatants induced cardiac myocyte injury, which was characterized by a significant (P < 0.01) reduction in cell viability to 53 +/- 3%, vs. 84 +/- 3% in rat myocytes subjected to hypoxia-reoxygenation (H/R) alone. The PMN supernatants also resulted in elevated creatine kinase (CK) activities in the myocyte medium. To examine specific PMN-released mediators that may contribute to this cell death, we studied the effects of hydrogen peroxide (H2O2), elastase, and platelet-activating factor on H/R cardiac myocytes. Incubation of myocytes after hypoxia with 10, 50, and 100 microM H2O2 decreased viability in a concentration-dependent manner (from 83 +/- 2 to 37 +/- 2%; P < 0.01). CK release of H/R myocytes was also significantly increased by 100 microM H2O2 (to 28 +/- 5 from 12 +/- 1% for H/R alone; P < 0.01). Similarly, elastase (5 micrograms/ml) given after hypoxia significantly reduced cardiac myocyte viability during reoxygenation (viability 58 +/- 1 vs. 85 +/- 1% H/R alone; P < 0.05) and increased CK release (to 29 +/- 3 from 11 +/- 1% for H/R alone; P < 0.01), an effect that was abolished by L-680,833, an elastase inhibitor. Unlike H2O2 and elastase, platelet-activating factor had no significant effect on myocyte viability or CK release after H/R.(ABSTRACT TRUNCATED AT 250 WORDS)