Blockade Of Prostaglandins And Nitric Oxide In-vivo Reduces State 3 Mitochondrial Respiration In Human Skeletal Muscle

Abstract

PURPOSE: The purpose of this study was to examine in humans the independent and combined effect of NO and PG blockade with L-NMMA and Indomethacin (Indo) on mitochondrial respiration in muscle from biopsies of the vastus lateralis (VL) following knee extension (KE) exercise. METHODS: Mitochondrial respiration was measured ex-vivo by high resolution respirometry in saponin-permeabilized fibers following 6 min KE in control (CON, n=8), arterial infusion of LNMMA (n=4) and Indo (n=4) randomized in order, followed by combined inhibition of NO and PG (L-NMMA + Indo, n=8). RESULTS. ADP-stimulated state 3 respiration with substrates for complex I (glutamate, malate) was reduced 50% by Indo compared to CON. State 3 O2 flux with convergent electron input through both complex I and II with addition of succinate was equally reduced with Indo (20%) and L-NMMA + Indo (15%) compared to CON and LNMMA alone. Uncoupled O2 flux determined by titration of the ionophore FCCP was not increased above state 3 respiration with Indo suggesting tight coupling to oxidative phosphorylation. Graded titrations of L-NMMA into the respirometer in CON muscle reduced state 3 respiration by 12% only at a supra-physiological dose, while titration of Indo caused a linear reduction at all doses within and above the physiological range. CONCLUSION: The results indicate that inhibition of PG by indomethacin inhibits state 3 mitochondrial respiration primarily at complex I of the respiratory chain. This effect may in part explain the in-vivo reduction in muscle O2 uptake during exercise with double blockade of NO and PG, since blockade of NO by L-NMMA counteracts the inhibitory effect of Indo.