GLUCOSE-STIMULATED AND PHORBOL-MYRISTATE ACETATE-STIMULATED OXYGEN-CONSUMPTION AND SUPEROXIDE PRODUCTION IN RAT PERITONEAL-MACROPHAGES IS INHIBITED BY DEXAMETHASONE

1. Rat peritoneal macrophages stimulated with phorbol 12-myristate 13- acetate (PMA) (40 nM) show an increase in the rate of oxygen consumpti on (measured with an O2 electrode) and the production of superoxide (m easured by cytochrome c reduction), which are both dependent on the pr esence of exogenous glucose. There is a 1:1 correlation between the ox ygen consumed and the superoxide produced over a range of glucose conc entrations (0-10 mM). 2. Preincubation of macrophages with dexamethaso ne (1 muM) for 3 h significantly decreased the V(max), for PMA-induced glucose-dependent oxygen consumption (P < 0.001) and glucose-dependen t superoxide production (P < 0.001). However, dexamethasone did not si gnificantly change the K(m) for glucose in either PMA-induced oxygen c onsumption or superoxide production. Dexamethasone is therefore a non- competitive inhibitor of PMA-stimulated glucose-dependent oxygen consu mption (K(i) = 0.83 +/- 0.09 muM) and superoxide generation (K(i) = 0. 87 +/- 0.09 muM). 3. The PMA-induced rate of oxygen consumption by mac rophages was decreased at oxygen concentrations below approx. 15 muM. The K(m) of oxygen for PMA-induced oxygen consumption was 1.28 +/- 0.1 3 muM (n = 12), and this was not significantly different in the presen ce of dexamethasone; K(m) = 1.61 +/- 0.31 muM (n = 12). It is therefor e concluded that in vivo macrophage superoxide production is not limit ed by external oxygen or glucose concentrations, even in hypoxic joint s.