Protein turnover in tissues of diabetic rats.

Rates of protein breakdown in tissues of diabetic rats were estimated by measuring the rates of protein synthesis and growth of protein mass. Measurements were made after withdrawal of insulin from streptozotocin diabetic rats that had been maintained with daily insulin injections. In muscle of the control (insulin treated) rats there was rapid catch up growth associated with increased protein synthesis and decreased breakdown. Insulin withdrawal resulted in a loss of protein, a decreased rate of synthesis and an elevated rate of breakdown. In the liver of the insulin withdrawn rats there was an immediate loss of protein associated with reduced synthesis and increased breakdown, but after two days the protein loss ceased and breakdown was also depressed. The response of kidney to insulin withdrawal was an increase in protein mass, brought about entirely by an inhibition of proteolysis.