Glucose-6-phosphate dehydrogenase (G6PD) is a determinant in the antioxidant status of the red blood cell (RBC) and is also used as an indicator of cell age. However, it is unknown if the relationship among antioxidant status, cell age, and RBC-derived adenosine triphosphate (ATP) occurs immediately or over a period of time. Therefore, the development of a simultaneous determination of G6PD activity (via the determination of nicotinamide adenine dinucleotide phosphate (NADPH)) in RBCs and the determination of deformation-induced RBC-derived ATP is described. The NADPH and ATP were determined while undergoing a chemically induced aging process via inhibition of G6PD with dehydroepiandroesterone (DHEA). Upon incubation with DHEA for 30 min, NADPH levels measured in a flow stream decreased to 7.96+/-1.10 microM from an original value of 13.20+/-1.80 microM in a 0.02% solution of RBCs. In order to demonstrate a direct relationship between G6PD activity and deformation-induced ATP release from RBCs, a simultaneous microflow determination of G6PD activity and ATP release was performed. Upon inhibition with DHEA, NADPH levels decreased to 8.62+/-0.29 microM from its original value of 12.73+/-0.50 microM while ATP release decreased from 0.21+/-0.07 microM to 0.06+/-0.02 microM. These values were validated by an examination of NADPH levels in, and ATP release from, RBC fractions containing younger and older cells (separated by cell density centrifugation). This determination provides evidence that antioxidant status in the RBC and its ability to release ATP, a known stimulus of nitric oxide production, are closely related.