Glucose-6-phosphate dehydrogenase activity in individual rat hepatocytes of different ploidy classes. II. Time-dependent variations during 24 h.

The time-dependent variation of glucose-6-phosphate dehydrogenase (G6PDH) activity during 24 h has been investigated by cytophotometric analysis in cytochemically stained, isolated hepatocytes of different ploidy classes from adult male rats. It was found that the amplitude of the variation in the total amount of parenchyma was 22%, with a maximum in the middle of the resting phase of the animals (13%). This small variation could not be detected subjectively in cryostat sections of liver that had been stained histochemically; nor could a metabolic zonation of the liver parenchyma be observed except the intermediate zone, which stained more strongly for G6PDH activity at 13% and 22%. The quantitative study on the isolated hepatocytes, however, revealed a relatively strong variation of 48% during the day in enzyme activity of the mononuclear diploid cells and no significant variation in the binuclear tetraploid cells. The cells of the in-between ploidy classes showed an amplitude of variation of 38% (binuclear diploid cells) and 24% (mononuclear tetraploid cells). All cells showed a maximum activity at 13% and a minimum activity during the night. It is concluded that this ploidy-dependent variation might play a role in the generation of pentoses for RNA synthesis. The findings indicate that for metabolic studies the heterogeneity of the liver parenchyma should be taken into account with respect to the different ploidy classes, as well as the well-known metabolic zonation of the acinus.