Determination of the nuclear RNA content of cells from donors of three different ages during in vitro senescence.

Diploid fibroblasts from male donors aged 8, 40 and 84 years were grown in vitro and their nuclear RNA content was determined at early and late doublings by absorption cytophotometry after staining with Azure B for 2 hours at 40 degree C and pH 4. It was found that the average nuclear RNA content of the early doublings was lower than that of the last doubling in all three strains. This difference became smaller as donor age increased. Also, as the age of the donor increased the percentage of early passage cells with a relative nuclear RNA content of less than 6 arbitrary units decreased, those with a relative nuclear RNA content of more than 6 units increased and the diversity in nuclear RNA content increased. The distribution pattern of relative RNA content for late passage cells was similar for the three donors.