Angiotensin mediates forearm glucose uptake by hemodynamic rather than direct effects

Insulin sensitivity may be improved with the angiotensin-converting enzyme inhibitor captopril, suggesting that inhibition of angiotensin II (Ang II) improves insulin resistance. However, the administration of systemic Ang II has also been associated with an improvement in rather than worsening of glucose utilization. Since both stimulating and antagonizing the renin-angiotensin system improve glucose uptake and both angiotensin-converting enzyme inhibitors and intravenous Ang II elicit skeletal muscle vasodilation, it is conceivable that hemodynamic factors rather than a direct effect of either Ang II or angiotensin-converting enzyme inhibitors on skeletal muscle metabolism modulate the increase in glucose utilization. The direct effects of Ang II on glucose extraction in intact human skeletal muscle have not been previously described. We investigated the effects of local infusion of Ang II on glucose uptake in the forearm of 20 healthy subjects. With the use of the isolated insulin-perfused forearm model, local plasma insulin values were raised to 100 mU/mL over fasting values and maintained there for a 90-minute infusion period. After the first 60 minutes of insulin alone, Ang II was infused into the brachial artery for the last 30 minutes. Intra-arterial Ang II infusion caused a 38% decrease in forearm blood flow (P <.05) and 59% increase in the arteriovenous glucose gradients (P <.05) to maintain a steady glucose utilization (a decrease of 4%, P=NS). Thus, local Ang II infusion does not impair insulin-stimulated glucose utilization. Furthermore, glucose extraction increases to compensate for the decrease in forearm blood flow (as the Fick principle would predict for freely diffusible substances). We conclude that the described increase in glucose utilization from systemic infusion of Ang II and during angiotensin-converting enzyme inhibitor treatment is mediated by hemodynamic factors rather than a direct effect of Ang II on skeletal muscle metabolism.