Hypertonic glycerol induces a respiratory burst in leukocytes

Exposure to hypertonic glycerol induced cyanide-insensitive oxygen consumption and formation of superoxide anion (O-2) in leukocytes such as porcine blood polymorphonuclear leukocytes, guinea pig peritoneal leukocytes and guinea pig alveolar macrophages. Generation of O-2 occurred after a short lag time, remained maximal for a certain time and then stopped. Its termination was not due to cell damage, since cells exposed to glycerol did not release cytosolic enzymes such as lactate dehydrogenase and exhibited a subsequent respiratory burst upon addition of other stimulators such as myristic acid and phorbol myristate acetate. The period of O-2 generation increased linearly as a function of the glycerol concentration; cells exposed to 20% (v/v) glycerol produced O-2 for 10 min. The maximal velocity of O-2 generation also increased with the concentration of glycerol, reaching a plateau at 10% glycerol. Membrane vesicles isolated from the cells exposed to 20% glycerol showed high activity of NADPH-dependent O-2 generation as compared to those of unexposed cells. Activation of leukocytes by glycerol was not accompanied by degranulation, unlike stimulation by phagocytosis. A marked change in shape of the cell membrane of glycerol-treated cells was observed by light and scanning electron microscopies.