title: Opposing effects of nitric oxide and prostaglandin inhibition on muscle mitochondrial Vo(2) during exercise.
abstract: Nitric oxide (NO) and prostaglandins (PG) together play a role in regulating blood flow during exercise. NO also regulates mitochondrial oxygen consumption through competitive binding to cytochrome-c oxidase. Indomethacin uncouples and inhibits the electron transport chain in a concentration-dependent manner, and thus, inhibition of NO and PG synthesis may regulate both muscle oxygen delivery and utilization. The purpose of this study was to examine the independent and combined effects of NO and PG synthesis blockade (L-NMMA and indomethacin, respectively) on mitochondrial respiration in human muscle following knee extension exercise (KEE). Specifically, this study examined the physiological effect of NO, and the pharmacological effect of indomethacin, on muscle mitochondrial function. Consistent with their mechanism of action, we hypothesized that inhibition of nitric oxide synthase (NOS) and PG synthesis would have opposite effects on muscle mitochondrial respiration. Mitochondrial respiration was measured ex vivo by high-resolution respirometry in saponin-permeabilized fibers following 6 min KEE in control (CON; n = 8), arterial infusion of N(G)-monomethyl-L-arginine (L-NMMA; n = 4) and Indo (n = 4) followed by combined inhibition of NOS and PG synthesis (L-NMMA + Indo, n = 8). ADP-stimulated state 3 respiration (OXPHOS) with substrates for complex I (glutamate, malate) was reduced 50% by Indo. State 3 O(2) flux with complex I and II substrates was reduced less with both Indo (20%) and L-NMMA + Indo (15%) compared with CON. The results indicate that indomethacin reduces state 3 mitochondrial respiration primarily at complex I of the respiratory chain, while blockade of NOS by L-NMMA counteracts the inhibition by Indo. This effect on muscle mitochondria, in concert with a reduction of blood flow accounts for in vivo changes in muscle O(2) consumption during combined blockade of NOS and PG synthesis.
authors.affiliation: Heart and Circulatory Unit, Department of Biomedical Sciences; Mitochondrial Research Laboratory, Department of Anaesthesia Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark. boushel@sund.ku.dk
authors.forename: Robert
authors.initials: R
authors.lastname: Boushel
authors.forename: Teresa
authors.initials: T
authors.lastname: Fuentes
authors.forename: Ylva
authors.initials: Y
authors.lastname: Hellsten
authors.forename: Bengt
authors.initials: B
authors.lastname: Saltin
mesh_terms: D045222:Electron Transport Chain Complex Proteins / Q000187:drug effects / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D008931:Mitochondria, Muscle / Q000187:drug effects* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D011448:Prostaglandin Antagonists / Q000494:pharmacology*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D055815:Young Adult; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D045222:Electron Transport Chain Complex Proteins; D011448:Prostaglandin Antagonists; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D010100:Oxygen; D007213:Indomethacin