Angiotensin-(1-7) recruits muscle microvasculature and enhances insulin's metabolic action via mas receptor

Abstract

Angiotensin-(1-7) [Ang-(1-7)], an endogenous ligand for the G protein-coupled receptor Mas, exerts both vasodilatory and insulin-sensitizing effects. In skeletal muscle, relaxation of precapillary arterioles recruits microvasculature and increases the endothelial surface area available for nutrient and hormone exchanges. To assess whether Ang-(1-7) recruits microvasculature and enhances insulin action in muscle, overnight-fasted adult rats received an intravenous infusion of Ang-(1-7) (0, 10, or 100 ng/kg per minute) for 150 minutes with or without a simultaneous infusion of the Mas inhibitor A-779 and a superimposition of a euglycemic insulin clamp (3 mU/kg per minute) from 30 to 150 minutes. Hind limb muscle microvascular blood volume, microvascular flow velocity, and microvascular blood flow were determined. Myographic changes in tension were measured on preconstricted distal saphenous artery. Ang-(1-7) dose-dependently relaxed the saphenous artery (P<0.05) ex vivo. This effect was potentiated by insulin (P<0.01) and abolished by either endothelium denudement or Mas inhibition. Systemic infusion of Ang-(1-7) rapidly increased muscle microvascular blood volume and microvascular blood flow (P<0.05, each) without altering microvascular flow velocity. Insulin infusion alone increased muscle microvascular blood volume by 60% to 70% (P<0.05). Adding insulin to the Ang-(1-7) infusion further increased muscle microvascular blood volume and microvascular blood flow (≈2.5 fold; P<0.01). These were associated with a significant increase in insulin-mediated glucose disposal and muscle protein kinase B and extracellular signal-regulated kinase 1/2 phosphorylation. A-779 pretreatment blunted the microvascular and insulin-sensitizing effects of Ang-(1-7). We conclude that Ang-(1-7) by activating Mas recruits muscle microvasculature and enhances the metabolic action of insulin. These effects may contribute to the cardiovascular protective responses associated with Mas activation and explain the insulin-sensitizing action of Ang-(1-7).

Keywords: angiotensins; endothelial cells; microvasculature; muscles.

Figure 1

Experimental protocols. Protocol 1 examines Ang-(1-7)’s effects on muscle microvasculature. Protocol 2 studies whether Ang-(1-7) alters insulin’s microvascular and metabolic actions. Protocol 3 determines whether Mas mediates Ang-(1-7)’s microvascular actions.

Figure 2

Ang-(1-7) induces vasodilation via endothelium- and Mas-dependent mechanisms. Rat distal saphenous artery was isolated, pre-constricted with phenylephrine, and then incubated with various concentrations of Ang-(1-7) and/or insulin. A and B: Effect of Ang-(1-7) on intact or endothelium denuded arterial rings. n=6, * p<0.05. C and D: Effect of insulin. n=6, * p<0.05 vs. control. E and F: Effect of Ang-(1-7) in the presence of insulin (1 nM). n=6, #p<0.01 vs. control. G and H: Effect of Mas inhibition on Ang-(1-7)-induced vasodilation. n=6, * p<0.05. B, D, F and H: representative myographic tracings.

Figure 3

Effects of Ang-(1-7) on muscle microvascular recruitment. Each rat received a continuous intravenous infusion of Ang-(1-7) or saline (Control) for 150 min (−30 – 120 min). Ang-(1-7)_10: Ang-(1-7) at 10 ng/kg/min. Ang-(1-7)_100: Ang-(1-7) at 100 ng/kg/min. A: MBV; B: MFV; C: MBF. n=5 each. * p<0.05 vs control.

Figure 4

Effects of Ang-(1-7) on muscle microvascular recruitment during insulin clamp. Each rat received a continuous intravenous infusion of Ang-(1-7) or saline (Control) for 150 min (−30 – 120 min) with an insulin clamp (3 mU/kg/min) superimposed on the last 120 min. Ang-(1-7)_10: Ang-(1-7) at 10 ng/kg/min. Ang-(1-7)_100: Ang-(1-7) at 100 ng/kg/min. A: MBV; B: MFV; C: MBF. n=5 each. * p<0.05 vs baseline (−30 min). # p<0.01 vs insulin alone.

Figure 5

Ang-(1-7) dose-dependently augments insulin-stimulated whole body glucose disposal. Each rat received a continuous intravenous infusion of Ang-(1-7) or saline (Control) for 150 min with an insulin clamp (3 mU/kg/min) superimposed on the last 120 min. Ang-(1-7)_10: Ang-(1-7) at 10 ng/kg/min. Ang-(1-7)_100: Ang-(1-7) at 100 ng/kg/min. A: Time course of glucose infusion rate (GIR) during insulin clamp; B: GIR area under the curve during insulin clamp. n=5 each. * p<0.05 vs control.

Figure 6

Effects of Mas inhibition on Ang-(1-7) and insulin’s microvascular actions. Each rat received a continuous intravenous infusion of A-779 (10 nmol/kg/min) 30 min before Ang-(1-7) or saline infusion and 60 min before insulin clamp (3 mU/kg/min). Ang-(1-7)_10: Ang-(1-7) at 10 ng/kg/min. Ang-(1-7)_100: Ang-(1-7) at 100 ng/kg/min. A: MBV; B: MFV; C: MBF. n=5 each. * p<0.05 vs baseline (−60 min), # p<0.05 vs insulin alone.

Figure 7

Mas inhibition abolishes Ang-(1-7)-mediated enhancement in insulin’s metabolic action. Each rat received a continuous intravenous infusion of A-779 (10 nmol/kg/min) 30 min before Ang-(1-7) or saline infusion and 60 min before insulin clamp (3 mU/kg/min). Ang-(1-7)_10: Ang-(1-7) at 10 ng/kg/min. Ang-(1-7)_100: Ang-(1-7) at 100 ng/kg/min. A: Time course of glucose infusion rate (GIR) during insulin clamp; B: GIR area under the curve during insulin clamp. n=5 each.

Figure 8

Effect of Ang-(1-7) on muscle Akt and ERK1/2 phosphorylation. A: Akt phosphorylation. B: ERK1/2 phosphorylation. n=4 each. * p<0.05 vs baseline [no insulin or A-779], # p<0.05 vs insulin alone.