RESUMO
The effect on mitochondria isolated from corpus luteal tissues following priming of immature female rats with pregnant mares serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) was studied. Ultrastructural studies showed intramitochondrial filamentous nucleic acid networks in situ following intense uranyl acetate staining. The intramitochondrial complexes were sensitive to nuclease treatment. Primed corpora lutea contained a 3.7-fold increase of mitochondrial DNA (mtDNA) per mg of mitochondrial protein when compared to unprimed ovaries. In subsequent experiments female rats were injected with 3H-thymidine 12 h before harvesting gonadotropin-primed corpora lutea from which mitochondria were isolated, purified and lysed. MtDNA was isolated and purified from the lysate by CsCl-ethidium bromide equilibrium buoyant density gradient centrifugation. Both the upper and lower bands of mtDNA as well as the intermediate region of the gradient contained radioactive label. When mtDNA from a fractionated gradient was mounted for electron microscopy and examined, replicative forms of mtDNA were observed. The mechanism of replication appears to be by the displacement-loop model of mtDNA replication. Ultrastructural as well as biochemical evidence indicate that a consequence of corpora lutea formation is the replication of mtDNA.
