Exercise-induced alterations of hepatic mitochondrial function.

In order to examine the effect of a single bout of exercise on hepatic mitochondrial function, starved untrained male rats swam at 34-35 degrees C with a tail weight (5% of body wt.) for 100 min. The rates of ADP-stimulated and uncoupled respiration were higher in the mitochondria isolated from the exercised rats regardless of the substrate utilized. Succinate-linked Ca2+ uptake was 48% greater in the exercised group; however, Ca2+ efflux was markedly depressed. The inhibition of Ca2+ uptake by Mg2+ was higher in the control group, so that the difference in Ca2+ uptake between the two groups was greater in the presence of Mg2+ than in its absence. The response of phosphorylating respiration and Ca2+ fluxes to exogenous phosphate and the pH of the assay medium differed in the exercise group. These observations with the exercised group were not related to non-specific stress. The exercise-induced mitochondrial-functional alterations are reminiscent of those obtained from mitochondria isolated from glucagon- or catecholamine-treated sedentary rats. Thus, adrenergic stimulation as well as other factors may be operating during exercise, leading to an alteration of mitochondrial function in vitro.