Effects of growth hormone on respiration and ATPase activity of rat liver and heart mitochondria

The effects of hypophysectomy on respiration and ATPase activity of mitochondria of rat heart and liver were investigated. Hypophysectomy decreased significantly the rate of State 3 respiration and ATPase activity of liver but not of heart mitochondria. Heart cytochrome oxidase activity was also not affected. ADP:O and respiratory control ratios were not affected. Administration of bovine growth hormone (bGH) to hypophysectomized rats partially restored the rate of respiration and ATPase activity of liver mitochondria. However, hypophysectomy decreased heart mitochondrial protein synthesis as measured by in vivo and in vitro incorporation of radioactive leucine, but did not affect the in vitro uptake of the amino acid. Administration of bGH restored the incorporation capacity to the normal level. Similar effects on liver mitochondrial protein synthesis have already been reported. These data suggest that the effects of growth hormone on mitochondrial function may vary with the two tissues.