Effects of indomethacin on respiration and the α-glycerolphosphate shuttle in rat kidney mitochondria

The anti-inflammatory drug indomethacin was found to stimulate State 4 respiration in rat kidney mitochondria, indicating an uncoupler activity which was maximal at a concentration of 0.1–0.2mM. Indomethacin also inhibited State 3 respiration in mitochondria oxidizing glutamate or succinate, but not in mitochondria oxidizing ascorbate together with tetramethylphenylene diamine. This inhibition was not relieved by 2,4-dinitrophenol and suggested that indomethacin directly inhibited electron transport along the respiratory chain at a point prior to cytochrome c. At concentrations one order of magnitude lower than that required for substantial uncoupling or respiratory inhibition, indomethacin severely restricted the transfer of reducing equivalents from extramitochondrial NADH to the respiratory chain via a reconstructed α-glycerolphosphate shuttle. It was found that the drug exerted a strong inhibitory effect on mitochondrial α-glycerolphosphate dehydrogenase activity, and that this inhibition was relatively specific since indomethacin had little effect on the activity of succinate dehydrogenase, another FAD-linked enzyme. The inhibition of the α-glycerolphosphate shuttle is discussed in relation to the previously observed effects of indomethacin on glucose metabolism in isolated rat kidney tubules.