Nitric oxide-mediated augmentation of polymorphonuclear free radical generation after hypoxia-reoxygenation

Polymorphonuclear leukocytes (pMNLs), nitric oxide (NO), calcium, and free radicals play an important role in hypoxia/ischemia and reoxygenation injur y. In the present study, NO donors, sodium nitroprusside (SNP), and diethyl amine-NO (DEA-NO) at low concentrations (10 and 100 nmol/L) potentiated, wh ile higher (10 mu mol/L to 10 mmol/L) concentrations inhibited free radical generation response in the rat PMNLs. Free radical generation response was found to be significantly augmented when hypoxic PMNLs were reoxygenated ( hypoxia-reoxygenation [H-R]), This increase in free radical generation afte r reoxygenation or SNP (10 nmol/L) was blocked in the absence of extracellu lar calcium. SNP (10 nmol/L) or H-R-mediated increases in the free radical generation were prevented by the pretreatment of PMNLs with NO scavenger (h emoglobin), the polyadenine diphosphate (ADP)ribosylation synthase inhibito r (benzamide) or the calcium channel antagonist (felodipine), A significant augmentation in the nitrite and intracellular calcium levels was observed during hypoxia. Hemoglobin pretreatment also blocked the increase in intrac ellular calcium levels due to SNP (10 nmol/L) or hypoxia. Thus, increased a vailability of NO during SNP treatment or H-R, may have led to an ADP-ribos ylation-mediated increase in intracellular calcium, thereby increasing the free radical generation from the rat PMNLs. (C) 1999 by The American Societ y of Hematology.