Acute effect of the dual angiotensin-converting enzyme and neutral endopeptidase 24-11 inhibitor mixanpril on insulin sensitivity in obese Zucker rat

Abstract

The aim of this study was to determine whether acute dual angiotensin-converting enzyme (ACE)/neutral endopeptidase 24-11 (NEP) inhibition could improve whole body insulin-mediated glucose disposal (IMGD) more than ACE inhibition alone and whether this effect was mediated by the kinin-nitric oxide (NO) pathway activation. We therefore compared in anaesthetized obese (fa/fa) Zucker rats (ZOs) the effects of captopril (2 mg kg(-1), i.v.+2 mg kg(-1) h(-1)), retrothiorphan (25 mg kg(-1), i.v. +25 mg kg(-1) h(-1)), a selective NEP inhibitor, and mixanpril (25 mg kg(-1), i.v. +25 mg kg(-1) h(-1)), a dual ACE/NEP inhibitor, on IMGD using hyperinsulinaemic euglycaemic clamp technique. The role of the kinin-NO pathway in the effects of mixanpril was tested using a bradykinin B2 receptor antagonist (Hoe-140, 300 microg kg(-1)) and a NO-synthase inhibitor (N(omega)-nitro-L-arginine methyl ester, L-NAME, 10 mg kg(-1) i.v. +10 mg kg(-1) h(-1)) as pretreatments. Insulin sensitivity index (ISI) was lower in ZO controls than in lean littermates. Increases in ISI were observed in captopril- and retrothiorphan-treated ZOs. In mixanpril-treated ZOs, ISI was further increased, compared to captopril- and retrothiorphan-treated ZOs. In ZOs, Hoe-140 and L-NAME alone did not significantly alter and slightly reduced the ISI respectively. Hoe-140 and L-NAME markedly inhibited the ISI improvement induced by mixanpril. These results show that in obese insulin-resistant Zucker rats, under acute conditions, NEP or ACE inhibition can improve IMGD and that dual ACE/NEP inhibition improves IMGD more effectively than does either single inhibition. This effect is linked to an increased activation of the kinin-NO pathway.

Figure 1

Blood glucose concentrations (A) and Glucose Infusion Rate (GIR, B) required for maintaining euglycaemia during glucose clamp study at insulin infusion rate of 15 mu kg⁻¹ min⁻¹ in obese and lean Zucker rats: Effects of captopril (2 mg kg⁻¹, i.v. bolus+2 mg kg⁻¹ h⁻¹ infusion), retrothiorphan (25 mg kg⁻¹, i.v. bolus+25 mg kg⁻¹ h⁻¹ infusion) and mixanpril (25 mg kg⁻¹, i.v. bolus+25 mg kg⁻¹ h⁻¹ infusion) in the obese Zucker rats (experiment 1). In A, s.e.mean were not shown for clarity and ranged from 1.8–9.8%. In B, each point represent the mean value of n rats (n=5–6) and the vertical T bar the s.e.mean.

Figure 2

Insulin Sensitivity Index (ISI, mg glucose kg⁻¹ min⁻¹ μu insulin⁻¹ ml⁻¹×1000) at the steady-state of the 2-h euglycaemic hyperinsulinaemic clamp (15 mu kg⁻¹ min⁻¹) in obese and lean Zucker rats. Effects of captopril (CAP, 2 mg kg⁻¹, i.v. bolus+2 mg kg⁻¹ h⁻¹ infusion), retrothiorphan (RT, 25 mg kg⁻¹, i.v. bolus+25 mg kg⁻¹ h⁻¹ infusion) and mixanpril (MIX, 25 mg kg⁻¹, i.v. bolus+25 mg kg⁻¹ h⁻¹ infusion) in the obese Zucker rats (experiment 1). For each rat, ISI was determined from the ratio: GIR_{90–120 min} (mg kg⁻¹ min⁻¹)/steady-state plasma insulin (μu ml⁻¹) ×1000. Each column represents the mean value of n rats (n=5–6) and the vertical bar the s.e.mean. *P<0.05, **P<0.01 and ***P<0.01 vs obese+vehicle; ##P<0.01 vs obese+captopril, †††vs obese+retrothiorphan (ANOVA followed by Newman-Keuls test).

Figure 3

Blood glucose concentrations (A) and Glucose Infusion Rate (GIR, B) required for maintaining euglycaemia during glucose clamp study at insulin infusion rate at 15 mu kg⁻¹ min⁻¹ in obese and lean Zucker rats: Effects of captopril (2 mg kg⁻¹, i.v. bolus+2 mg kg⁻¹ h⁻¹ infusion), mixanpril (25 mg kg⁻¹, i.v. bolus+25 mg kg⁻¹ h⁻¹ infusion), Hoe-140 (300 μg kg⁻¹) in combination with mixanpril and L-NAME (10 mg kg⁻¹, i.v. bolus+10 mg kg⁻¹ h⁻¹ infusion) in combination with mixanpril in the obese Zucker rats (experiment 2). In A, s.e.mean were not shown for clarity and ranged from 0.4–8.8%. Each column represents the mean value of n rats (n=5–6) and the vertical bar the s.e.mean.

Figure 4

Insulin Sensitivity Index (ISI, mg glucose kg⁻¹ min⁻¹ μu insulin⁻¹ ml⁻¹×1000) at the steady-state of the 2-h euglycaemic hyperinsulinaemic clamp (15 mu kg⁻¹ min⁻¹) in obese Zucker rats. Effects of captopril (CAP, 2 mg kg⁻¹, i.v. bolus+2 mg kg⁻¹ h⁻¹ infusion), mixanpril (MIX, 25 mg kg⁻¹, i.v. bolus+25 mg kg⁻¹ h⁻¹ infusion), Hoe-140 alone (Hoe, 300 μg kg⁻¹) or in combination with MIX and L-NAME (L-N, 10 mg kg⁻¹, i.v. bolus+10 mg kg⁻¹ h⁻¹ infusion) alone or in combination with MIX in the obese Zucker rats (experiment 2). For each rat, ISI was determined from the ratio: GIR_{90–120 min} (mg kg⁻¹ min⁻¹)/steady-state plasma insulin (μu ml⁻¹)×1000. Results are expressed as mean values of n rats (n=5–8)±s.e.mean. **P<0.01 and ***P<0.01 vs obese+vehicle; †P<0.05 vs obese+captopril; ###P<0.001 vs obese+mixanpril; ‡‡‡P<0.001 vs obese+L-N (ANOVA followed by Newman-Keuls test).