The effect of diabetes and insulin on the polyadenylic acid-containing RNA of rat skeletal muscle.

Poly(A)-containing RNA in various fractions of RNA from rat skeletal muscle has been detected and quantitated by hybridization to [3H]poly(U). Comparison has been made between the RNA in skeletal muscle from normal adult rats, from rats 2 days after induction of diabetes with streptozotocin, and from diabetic rats killed 60 min after injection of insulin. The poly(A)-containing RNA constituted a similar proportion of the total RNA in skeletal muscle from each of the three types of rats. In diabetes there was a decrease in the proportion of skeletal muscle ribosomes sedimenting as polyribosomes, but this was reversed after rats had been injected with insulin. However these changes were not associated with any alterations in the relative amounts of poly(A)-containing RNA in ribosomes isolated from rat skeletal muscle. Diabetes did not significantly alter the size distribution of the poly(A)-containing RNA or its poly(A) segment. If it is assumed that poly(A)-containing RNA is mRNA, these results imply that insulin stimulates protein synthesis in the skeletal muscle of diabetic rats by affecting the translation of pre-existing mRNA. Sucrose density gradient analysis showed that there was less poly(A)-containing RNA in the polyribosome region from diabetic rats than there was in that from normal rats. The balance of the poly(A)-containing RNA in the ribosomes from diabetic rats (presumed to be the untranslated mRNA) was found associated with rapidly sedimenting aggregated ribosomes, but its native form has not yet been determined.