Respective roles of nitric oxide and superoxide radical in the respiratory burst activity of rat polymorphonuclear leukocytes induced by hyperthyroidism.

Administration of single doses of 0.1 mg of L-3,3',5-triiodothyronine (T3)/kg for 3 consecutive day to fed rats elicited a marked increase both in the opsonized zymosan-induced luminal-amplified integrated chemiluminescence (ICL) of isolated polymorphonuclear leukocytes (PMN) in the absence (200%) and presence (228%) of L-arginine, and in the rate of superoxide radical (O2(.-)) production (180%). In the presence of L-arginine, the ICL was significantly increased by 57 and 17% over values observed in its absence, in PMN from control rats and T3-treated animals, respectively, an effect that was completely abolished by Nω-nitro-L-arginine. However, the net L-arginine-dependent ICL was comparable in stimulated PMN from both experimental groups, and the respective rates of nitric oxide (NO(.)) production were not significantly different, either in the absence or presence of nitro-L-arginine methyl ester. It is concluded that thyroid hormone-induced respiratory burst activity of rat PMN is not dependent on changes in NO(.) synthase activity, but rather on the adaptive increase in O2(.-) generation by NADPH oxidase.