Effect of diabetes and protein malnutrition on the rate of muscle protein breakdown in rats.

Male streptocozin diabetic rats were fed ad libitum in two diets, one a control, adequate in protein and energy, and another, depleted in protein, but adequate in energy. Within each one of these dietary groups, three hormone-treated groups were made as follows: rats receiving vehicle, or 0.25 or 0.50 I.U. insulin/100 g body weight/day i.p. for 21 days. A fourth group of intact rats, receiving vehicle injection, was included as a control. Every day urine excretion was collected for urea-N and 3-methylhistidine (3-Mehis) determination. Body weight and food intake were recorded daily. At the end of the experiment, all animals were sacrificed, and a sample of blood was taken for plasma insulin assay. Liver, as well as gastrocnemius, soleus and extensor digitorum longus muscles were excised and weighed. Results showed that diabetic animals had a reduced body weight gain, although the food intake was elevated in all groups, as compared to the intact rats. Gastrocnemius and soleus muscle weights were, respectively, reduced and increased in the diabetic animals fed the low-protein diet. Urea-N output was elevated in all groups fed the control diet, but a marked reduction was observed in the protein depleted rats. A reduction in 3-Mehis output was displayed by the diabetic animals, specially those fed the low-protein diet. The results of this experiment showed that in streptocozin diabetic rats there was a reduction in the rate of myofibrillar protein breakdown, specially marked when fed a protein depleted diet.