Effect of triamcinolone treatment, starvation and diabetes on rat liver protein kinase activity

Triamcinolone administration for 3 days reduced protein kinase activity in normal and adrenalectomized rats by about one third. This was accompanied by a similar decrease in cyclic³H] AMP-binding capacity. Alloxan diabetes reduced protein kinase activity as well as cyclic³H] AMP-binding capacity by about 40%. Administration of insulin to diabetic rats produced an insignificant increase in protein kinase activity and did not improve cyclic³H] AMP-binding capacity. In fasted rats, there was a gradual decrease in protein kinase activity to about one half of initial activity on the fourth day, whereas the decrease in cyclic³H] AMP-binding capacity was less marked. The effect of starvation was observed in normal as well as adrenalectomized rats, indicating that the decrease due to fasting is not mediated by glucocorticoids. The findings suggest that the maintenance of liver protein kinase activity is under hormonal and nutritional control. This represents a long-term regulatory step at the stage of protein phosphorylation in addition to the rapid effect of hormones on cyclic AMP levels.