Angiotensin II inhibits glucose uptake of skeletal muscle via the adenosine monophosphate-activated protein kinase pathway

Abstract 

Adenosine monophosphate-activated protein kinase (AMPK) mediates metabolic responses of muscle to exercise and is involved in improvement of insulin resistance by endurance exercise. Recent studies have suggested that the renin-angiotensin system might negatively modulate insulin-mediated actions, but there has been little investigation of the correlation between the renin-angiotensin system and AMPK. To determine this correlation, we performed studies with glucose clamp in vivo, and glucose uptake by skeletal muscle ex vivo using 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). Six-week-old male Sprague-Dawley rats were fed standard chow (standard-diet rats; SD) or fructose-rich chow (fructose-fed rats; FFR) for 6 weeks. At the age of 12 weeks, SD and FFR were treated by oral gavage, either with angiotensin II (Ang II) receptor blockade (ARB; valsartan 30 mg/kg) or vehicle. Thirty minutes after the treatment, we performed glucose clamp studies to measure glucose infusion rates during infusion of insulin (GIR_I) and of AICAR (GIR_A), which stimulates AMPK, and studied the effect of ARB on either GIR_I or GIR_A. In an ex vivo study, we used bilateral fresh soleus muscles from 3-week-old male Sprague-Dawley rats to examine the glucose uptake (measured by ³H-2-deoxyglucose uptake) of one side of soleus muscle incubated with AICAR with or without Ang II, or with tumor necrosis factor-α, in comparison with that of the other (untreated control) side of the muscle. Blood pressure of FFR was significantly higher than that of SD rats. GIR_I was significantly lower in FFR than in SD, and treatment with ARB did not change GIR_I. GIR_A of FFR was significantly lower than that of SD, but GIR_A of FFR treated with ARB was significantly increased compared with that of FFR treated with vehicle. In the ex vivo study, incubation with AICAR significantly increased glucose uptake of soleus muscles, Ang II significantly decreased AICAR-activated glucose uptake in a dose-dependent manner, and ARB canceled the effect of Ang II. The results suggest that acute inhibition of the angiotensin 1 receptor improves glucose metabolism via not insulin but AMPK pathway through the angiotensin 1 receptor in FFR.

Keywords: AMP-activated protein kinase, renin-angiotensin system, insulin resistance, hypertension