Effect of pioglitazone on insulin receptors of skeletal muscles from high-fat-fed rats.

A new oral agent, 5-[4-[2-(5-ethyl-12-pyridyl)ethoxy]-benzyl]-2,4-thiazolidinedione, or pioglitazone, has been developed for the treatment of non-insulin-dependent diabetes mellitus (NIDDM). We examined its effectiveness in high-fat-fed rats resistant to insulin. Administration of the agent (10 mg.kg-1 x d-1) for 2 weeks resulted in decreases in hyperlipidemia and hyperinsulinemia, indicating that insulin sensitivity had increased in vivo in high-fat-fed rats. To clarify the mechanism of the drug, we examined insulin binding and kinase activity of insulin receptors from muscles of both untreated and treated high-fat-fed rats. Pioglitazone treatment did not change insulin binding in high-fat-fed rats, but increased insulin-stimulated autophosphorylation of insulin receptors to the level of control animals. Kinase activity toward an exogenous substrate, poly Glu4-Tyr1, in pioglitazone-treated high-fat-fed rats was also increased to the level of control animals. These results suggest that pioglitazone increases insulin sensitivity by activating tyrosine kinase activity of receptors in high-fat-fed rats, and this drug appears to be a useful one with a new mode of action for the treatment of NIDDM with insulin resistance.