Evidence that Glucagon Stabilizes rather than Activates Mitochondrial Functions in Rat Liver

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Abstract
Whether the acute treatment of intact rats or hepatocytes with glucagon and dibutyryl cAMP, respectively, leads to a stabilization or an activation of mitochondrial functions, such as state-3 respiration, succinate dehydrogenase activity and pyruvate carboxylase activity was examined. The influence of various parameters of mitochondria preparation (isolation medium, washing steps, storage) and of phospholipase A inhibitors (cinchocaine, chloroquine) on the expression of the hormone effect was examined. With regard to the above mentioned functions, the values displayed by control mitochondria were considerably higher if mannitol instead of sucrose had been used for isolation. Accordingly, only small effects of hormone treatment became apparent. The addition of cinchocain or chloroquine to the sucrose medium yielded results similar to those obtained with mannitol. The hormone effect on state-3 respiration and succinate dehydrogenase activity was only small if the mitochondria had been prepared faster than usual and had been used without washing. Regarding pyruvate carboxylase, a considerably smaller glucagon effect was observed when it was assayed at 25.degree. C and not (as usual) at 37.degree. C. Glucagon application evidently stabilizes rather than activates mitochondrial functions.

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