1. The luminol-dependent chemiluminescence of rat thymocytes responding to concanavalin A can be resolved into glucose-dependent and glucose-independent portions. 2. The glucose-dependent portion, supported by D-glucose and D-mannose oxidation, is inhibited by catalase (200 microgram/ml), amobarbital (1 mM) and hexose analogues that block D-glucose uptake. Thus concanavalin A may activate, transiently, an NAD(P)H oxidase that utilizes reducing equivalents derived from the oxidation of exogenous glucose to give dismutation products of O2- (including H2O2) as its major products. 3. The glucose-independent portion is inhibited by eicosa-5,8,11,14-tetraynoic acid but not by indomethacin. It may therefore be associated with the conversion of hydroperoxy intermediates of arachidonic acid metabolism to hydroxy products by the lipoxygenase pathway. 4. Preincubation of thymocytes for 18 h in serum-free medium enhances the subsequent chemiluminescent response to concanavalin A severalfold and evokes the response at a lower threshold concentration. The incorporation of [3H]thymidine by preincubated cells is similarly enhanced at low doses of concanavalin A, whereas the response to optimal doses is unaltered. 5. Catalase does not inhibit the enhanced incorporation of [3H]thymidine obtained in response to concanavalin A, but instead amplifies the response to low doses in the same manner as preincubation.

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