Morphological-cytochemical and molecular genetic analyses of mitochondria in isolated human oocytes in the reproductive age

Molecular genetic, cytochemical and morphometric analyses have been performed on isolated oocytes from 41 women (27-39 years of age) in order to detect mutations of mitochondria! DNA (mtDNA), defects of the respiratory chain (ubiquinone-cytochrome-c-oxidoreductase = complex III; cytochrome-c-oxidase = complex IV) and alterations of mitochondrial volume during cellular ageing. Morphometric analyses showed an increase in mitochondrial numerical density with age from the mean values of 7.36 per mu m(2) and 6.97 per mu m(3) up to 30 years to 10.74 per mu m(2) and 11.66 per mu m(3) in the age group 31-40 years (P <0.001). Similarly, an increase in the mitochondrial profile area from 0.074 per mu m(2) in the age group <30 years to 0.101 per mu m(2) was noted in the fourth decade. The mitochondrial volume fraction was also significantly increased in the elder age group. Neither point mutations of mtDNA (nucleotide pairs 3243, 8344) nor the common deletion (4977 bp, nucleotide pairs 8482-13460) could be detected. In parallel, ultra- and immunocytochemical studies of the complexes III-IV failed to reveal functional defects. In conclusion there is an age-related increase in the volume fraction of the mitochondria which might reflect subtle changes in the oxidative phosphorylation capacity, but is not linked to mutations of mtDNA or functional defects of the respiratory chain enzymes in mature human oocytes from women of reproductive age.