Effect of hypoxia on mitochondrial mass and cytochrome concentrations in rat heart and liver during postnatal development.

Cytochrome concentrations of rat heart and liver mitochondria were measured postnatally from newborn animals to young adults. Mitochondrial cytochrome aa3 concentration increased shortly after birth in both tissues, this concentration being in a newborn animal 0.149 +/- 0.027 nmol/mg protein in liver and 0.333 +/- 0.082 nmol/mg protein in heart. The respective values from a two week old animal were 0.216 +/- 0.031 and 0.583 +/- 0.100. Postnatally cytochromes c+c1 and b increased markedly in the heart, but in the liver of newborn animals the cytochrome content was more close to the adult values. The amount of mitochondrial protein increased after birth, too. In a newborn animal the mitochondrial protein values were 39.7 +/- 3.6 mg/g wet weight in liver and 26.6 +/- 6.5 mg/g wet weight in heart. In adult animals the respective values were 71.5 +/- 4.8 and 80.7 +/- 13.1. The effect of postnatal hypoxia (10% O2, 24 h and 48 h) on liver and heart mitochondrial cytochrome concentration and protein values of newborn animals were investigated. During hypoxia the amount of mitochondrial protein remained about at the level of a newborn animal. The postnatal increase in the mitochondrial cytochrome concentration, which was smaller in the liver than in the heart, was also inhibited by hypoxia.