Studies on the effect of anterior-pituitary growth hormone on oxidative phosphorylation in rat-liver mitochondria

Abstract

The efficiency of oxidative phos-phorylation in liver mitochondria from normal and growth hormone-treated rats has been measured with L-[beta]-hydroxybutyrate, reduced diphosphopyridine nucleotide or glutmate as substrate. There is a decrease in the efficiency when L-[beta]-hydroxybutyrate is used but not when reduced diphosphopyridine nucleotide or glutamate is substrate. The decreased P/O value is due to an increased rate of oxidation with no change in the rate of phosphorylation. There was no difference in the P/O ratio, with L-1-hydroxybutyrate as substrate, when digitonion particles isolated from normal and growth hormone treated animals were compared. Growth hormone at physiological concentrations produced striking increases in mitochondria permeability when added to mitochondria suspended in sucrose. The possibility that the effect of growth hormone on oxidative phosphorylation is secondary to an effect on mitochondrial permeability has been considered and the possible relationship between the effects of growth hormone and of thyroxine are discussed.