Altered activation of rat hepatic cyclic AMP-dependent protein kinases with increasing age

The activity ratio of hepatic cyclic AMP-dependent protein kinase has been found to change with increasing age in male, Long-Evans rats. In rats 35 days old (135 g), the activity ratio (cyclic AMP-dependent protein kinase activity measured in the absence and presence of exogenous cyclic AMP) was 0.76, it increased to 0.92 in rats 75 days old (315 g) and to 0.98 in rats 305 days old (646 g). This change in the activity ratio seems to correlate with the ability of aging animals to respond to a stimulus, and may be a primary mechanism in the biochemistry of aging.