PRODUCTION OF HYDROXYL RADICALS IN CONTRACTING SKELETAL-MUSCLE OF CATS

Reactive oxygen species increase during exhaustive contraction of skel etal muscle, but characterization of the specific species involved and their rates of production during nonexhaustive muscle contraction hav e not been investigated. We hypothesized that the production rate of h ydroxyl radical ((OH)-O-.) increases in contracting muscle and that th is rate is attenuated by pretreatment with deferoxamine (Def) or dimet hylthiourea (DMTU). We measured the rate of production of (OH)-O-. bef ore, during, and after 5 min of intermittent static contraction of the triceps surae muscles in cats (n = 6) using the formation of p-, m-, and o-tyrosines by hydroxylation of phenylalanine. L-Phenylalanine (30 mg/kg iv) was administered to each animal 3 min before contraction. B lood samples were collected from the popliteal vein 1 min before contr action; 1, 3, and 4.5 min during contraction; and 1 min after contract ion. During and after contraction, the cumulative production rates of p-, m-, and o-tyrosines were elevated by 42.84 +/- 5.41, 0.25 +/- 0.04 , and 0.21 +/- 0.03 nmol . min(-1). g(-1), respectively, compared with noncontracting triceps surae muscles. Pretreatment with Def (10 mg/kg iv; n = 5) or DMTU (10 mg/kg iv; n = 4) decreased the cumulative rate s of production of p-, m-, and o-tyrosines during and after contractio n. Additionally, the rate of tyrosine production increased in proporti on to the percentage of maximal tension developed by the triceps surae muscles. These results directly demonstrate that OH is produced in vi vo in the skeletal muscle of cats during intermittent static contracti on and that production can occur before the onset of fatigue.