EUGLYCEMIC HYPERINSULINEMIA AND HYPERAMINOACIDEMIA DECREASE SKELETAL-MUSCLE UBIQUITIN MESSENGER-RNA IN GOATS

Euglycemic hyperinsulinemia and hyperaminoacidemia decrease skeletal m uscle ubiquitin mRNA in goats. Am. J. Physiol. 271 (Endocrinol. Metab. 34): E505-E512, 1996.-Insulin inhibits protein breakdown at the whole body level, but neither the tissues nor the proteolytic pathways on w hich insulin exerts its antiproteolytic effect are well characterized. We measured the effects of insulin on mRNA levels for cathepsin D and m-calpain (a lysosomal and Ca2+-dependent proteinase, respectively) a nd ubiquitin (a component of ubiquitin-dependent proteolysis) in skele tal muscle, skin, liver, and intestine. We used a 6-h hyperinsulinemic , euglycemic, and hyperaminoacidemic clamp in goats, a species in whic h insulin markedly inhibited whole body protein breakdown under simila r conditions [S. Tesseraud, J. Grizard, E. Debras, I. Papet, Y. Bonnet , G. Bayle, and C. Champredon. Am. J. Physiol. 265 (Endocrinol. Metab. 28): E402-E413, 1993]. Hyperinsulinemia and hyperaminoacidemia had no effect on cathepsin D, m-calpain, and ubiquitin mRNA levels in liver, skin, and jejunum. In contrast, depressed ubiquitin mRNA levels were seen in skeletal muscle without any concomitant reduction in mRNA leve ls for cathepsin D, m-calpain, and other components of the ubiquitin-d ependent proteolytic pathway. The reduced ubiquitin mRNA levels in ske letal muscle may represent a possible mechanism explaining the antipro teolytic effect of insulin in vivo.