Studies of prostatic cytosol protein kinases of the aging ACI rat

Changes in prostatic cytosolic cyclic AMP (cAMP)-dependent and independent protein kinases associated with aging in ACI rats were determined. A decrease in prostatic weight and tissue protein content (but not DNA) with age was noted. The cytosolic cAMP-dependent protein kinase was present predominantly as the type II isozyme. Total content of this enzyme per prostate declined by 37% in 12-month-old rats but remained relatively stable thereafter. However, the activity ratio (+cAMP/-cAMP) increased with aging, indicating an elevation in the amount of the holoenzyme or a decrease in the amount of the free catalytic subunit. Concomitantly the specific activity (activity/unit protein in the cytosol) of this enzyme was found to be increased; this is most likely due to the loss of bulk proteins in the cytosol, and may indicate a slower loss of this enzyme protein in relation to other cytosolic proteins. By comparison, the cAMP-independent protein kinase demonstrated a marked and progressive decline in amount as well as in specific activity with aging, e.g. 80-90% decline at 12 months of age. The above changes in these enzymes did not appear to be due to low circulating androgen in the animals, since they were not reversed on administration of 3.0 mg of testosterone propionate per rat daily for four consecutive days. It is therefore suggested that the above-described changes in prostatic cytosolic protein kinases are primarily associated with cellular senescence in this organ.