HEART, LIVER, AND SKELETAL-MUSCLE MYELOPEROXIDASE ACTIVITY DURING EXERCISE

The purpose of his study was to determine whether contractile activity associated with running exercise was a prerequisite for neutrophil in filtration into rat tissues. H2O2-dependent myeloperoxidase (MPO) acti vity for rat (n = 8) liver, heart, and gastrocnemius muscles was assay ed after 58 +/- 11 min of running to voluntary exhaustion (25 m/min; 0 % grade). MPO activity values measured with 0.6 mM H2O2 were 0.988 +/- 0.331 (SD) U/g (skeletal muscle), 1.563 +/- 0.303 U/g (heart), and 1. 652 +/- 0.510 U/g (liver) for control samples, compared with 1.690 +/- 0.321, 3.128 +/- 1.221, and 2.752 +/- 0.437 U/g, respectively, for th e exercise group (P less than or equal to 0.05). Kinetic analysis reve aled that maximum velocity for all tissues increased as a result of th e exercise (P < 0.05). The Michaelis constant (K-m) values at rest for all tissues were similar (range 0.53-0.57 mM H2O2; P greater than or equal to 0.05). Exercise did not alter the K-m values for cardiac and liver samples; however, for skeletal muscle, the K-m was 28% lower tha n control (P less than or equal to 0.05). The results of this study sh ow that, with prolonged running, MPO activity is elevated in most rat tissues and not exclusively in skeletal muscle. Moreover, the metaboli c status of the tissues may be an important factor for neutrophil infi ltration with exercise and not exclusively the type of muscle contract ion, as previously hypothesized.