I n ischemia-reflow states of coronary artery disease, the activation of PMN precedes the initiation of tissue damage. Release of atrial natriuretic peptide (ANP) from myocytes occurs within minutes after the onset of myocardial ischemia, which suggests a possible role of ANP in PMN activation. To investigate this possibility, we tested the effects of ANP on functions of PMN in vitro. ANP is a potent signal for priming the PMN respiration burst to secrete superoxide anion. Phorbol 12-myristate 13-acetate, opsonized zymosan, or FMLP could all be used as triggering stimuli to demonstrate the priming of PMN activation by ANP. Only ANP fragments 1-28 and 7-28 enhanced respiration burst activity but identical preparations of ANP fragments 13-18 or 1-11 failed to do so. This structure-activity relationship is typical of receptors for ANP found in other tissues. In addition, ANP stimulated the release of beta-glucuronidase From PMN triggered by FMLP. The observed inhibition by ANP of FMLP-stimulated chemotaxis of PMN may be due to their enhanced adhesiveness. These data show that a classic cardiac hormone is involved in regulating important functional activities of PMN. These data support the possibility that ANP could act as a preinflammatory substance in ischemia-reperfusion states and myocardial necrosis.