Angiotensin II-induced insulin resistance is enhanced in adrenomedullin-deficient mice

Insulin resistance and hypertension are common disorders that are closely related. Among several factors, oxidative stress has been reported to be intimately related to these diseases. To elucidate the involvement of oxidative stress in the development of insulin resistance in a hypertensive model, we administered angiotensin II (Ang II), which raises blood pressure and induces reactive oxygen radicals, to adrenomedullin (AM)-knockout heterozygous mice and examined the resulting changes in blood pressure and insulin resistance. Ang II was administered ip at a dosage of 640 ng/kg.min for 4 wk. The systolic blood pressure was significantly elevated in both AM-knockout heterozygous and wild-type mice to the same extent. On the other hand, Ang II attenuated insulin sensitivity more strongly in AM-knockout heterozygous mice than in wild-type mice, when measured using 2- deoxyglucose uptakes in the soleus muscle. Ang II also induced a higher urinary excretion of isoprostane, a marker of oxidative stress. Furthermore, the production of oxidative stress in the soleus muscles of angiotensin-treated mice, measured using electronic spin resonance, was significantly higher than that in AM-knockout heterozygous mice. Moreover, 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, a superoxide scavenger mimetic, normalized the insulin resistance induced by Ang II without affecting the blood pressure in both groups. The present results suggest that, in an Ang II-treated mouse model, insulin resistance is induced by oxidative stress through a mechanism that is independent of blood pressure, and that AM can act as a protective peptide against insulin resistance via its intrinsic antioxidant effect.