Inhibitory effect of furosemide on activation of human peripheral blood polymorphonuclear leukocytes stimulated with n-formyl-methionyl-leucyl-phenylalanine.

The clinical efficacy of inhalatory furosemide (Fu) has been extensively studied in bronchial asthma patients but there are only a few studies addressing its action on cells participating in the underlying inflammatory process. Therefore, we investigated the effect of Fu on human peripheral blood polymorphonuclear leukocytes (PMNL) at concentrations that can be achieved in the bronchial lining fluid by inhalation, i.e. 10(-5), 10(-4) and 10(-3) M. The influence of Fu on the following PMNL parameters was investigated: intracellular calcium changes ([Ca2+]i) as a part of signal transduction and luminol dependent chemiluminescence (LCL) as an indirect measure of NADPH-oxidase activation upon n-formyl-methionyl-leucyl-phenylalanine (fMLP) stimulation; chemotaxis to fMLP, phagocytosis and intracellular killing of Staphylococcus aureus. Incubation with Fu resulted in a concentration dependent reduction of Ca2+ influx and Fu (10(-3) M) decreased the main Ca2+ parameters to one half of the control values and to the level obtained in calcium-free buffer. In contrast, Fu had no effect if preincubated with the cells and then removed by washing. The LCL signal was reduced by Fu (10(-3) M) from 2000 +/- 870 to 550 +/- 440 arbitrary units [aU] (p<0.05). In contrast to the [Ca2+]i measurements, a slightly diminished LCL was also observed following preincubation with Fu and washing. No effect of Fu was found on phagocytosis and intracellular killing of St. aureus. Fu diminished chemotaxis to fMLP but at 10(-3) M it also displayed weak chemoattractant properties. The differential action of Fu on human PMNL may add to the understanding of its topical and restricted efficacy in bronchial asthma.