Angiotensin-converting enzyme inhibitor increases insulin-induced pp185 phosphorylation in liver and muscle of obese rats

Angiotensin-(1–7) stimulates the phosphorylation of JAK2, IRS-1 and Akt in rat heart in vivo: role of the AT1 and Mas receptors

Angiotensin (ANG) II exerts a negative modulation on insulin signal transduction that might be involved in the pathogenesis of hypertension and insulin resistance. ANG-(1–7), an endogenous heptapeptide hormone formed by cleavage of ANG I and ANG II, counteracts many actions of ANG II. In the current study, we have explored the role of ANG-(1–7) in the signaling crosstalk that exists between ANG II and insulin. We demonstrated that ANG-(1–7) stimulates the phosphorylation of Janus kinase 2 (JAK2) and insulin receptor substrate (IRS)-1 in rat heart in vivo. This stimulating effect was blocked by administration of the selective ANG type 1 (AT1) receptor blocker losartan. In contrast to ANG II, ANG-(1–7) stimulated cardiac Akt phosphorylation, and this stimulation was blunted in presence of the receptor Mas antagonist A-779 or the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin. The specific JAK2 inhibitor AG-490 blocked ANG-(1–7)-induced JAK2 and IRS-1 phosphorylation but had no effect on ANG-(1–7)-induced phosphorylation of Akt, indicating that activation of cardiac Akt by ANG-(1–7) appears not to involve the recruitment of JAK2 but proceeds through the receptor Mas and involves PI3K. Acute in vivo insulin-induced cardiac Akt phosphorylation was inhibited by ANG II. Interestingly, coadministration of insulin with an equimolar mixture of ANG II and ANG-(1–7) reverted this inhibitory effect. On the basis of our present results, we postulate that ANG-(1–7) could be a positive physiological contributor to the actions of insulin in heart and that the balance between ANG II and ANG-(1–7) could be relevant for the association among insulin resistance, hypertension, and cardiovascular disease.

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

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.