Effect of Captopril, Losartan, and Bradykinin on Early Steps of Insulin Action

Abstract

Insulin initiates its metabolic and growth-promoting effects by binding to the alpha subunit of its receptor, thereby activating the kinase in the beta subunit. This event leads to tyrosyl phosphorylation of its cytosolic substrate, insulin receptor substrate 1 (IRS-1), which in turn associates with and activates phosphatidylinositol (PI) 3-kinase. The clinical use of ACE inhibitors has been associated with increased insulin sensitivity. However, the exact molecular mechanism is unknown. In the present study, we examined the phosphorylation status of the insulin receptor and IRS-1, as well as the association between IRS-1 and PI 3-kinase in the liver and muscle of 20-month-old rats treated acutely with captopril, using immunoprecipitation with antipeptide antibodies to the insulin receptor and IRS-1, and immunoblotting with antiphosphotyrosine and anti-PI 3-kinase antibodies. Insulin stimulation increased receptor autophosphorylation to 462 +/- 253% (P < 0.05) in the liver and 697 +/- 78% (P < 0.001) in the muscle of ACE inhibitor-treated rats. There were also increases to 250 +/- 17% (P < 0.001) and 280 +/- 50% (P < 0.05) in the insulin-stimulated IRS-1 phosphorylation levels in the liver and muscle, respectively, of animals treated with captopril. The insulin-stimulated IRS-1 association with PI 3-kinase rose to 305 +/- 20% (P < 0.001) in liver and 267 +/- 48% (P < 0.05) in muscle. Losartan, an ANG receptor blocker, had no significant effect on insulin-stimulated IRS-1 phosphorylation in both tissues. The acute administration of bradykinin increased insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1 in the liver and muscle. These data demonstrate that ACE inhibitors modulate the early steps of insulin signaling, and that this effect may be simulated by the administration of bradykinin.

Chronic resistance training decreases MuRF-1 and Atrogin-1 gene expression but does not modify Akt, GSK-3β and p70S6K levels in rats

“…The proteins were treated with Laemmli sample buVer containing dithiothreitol and boiled for 5 min before loading onto 8% SDS-PAGE in a Bio-Rad miniature slab gel apparatus. Similar sized aliquots (90 g) were subjected to SDS-PAGE as described elsewhere (Carvalho et al 1997). Electrotransfer of proteins from the gel to nitrocellulose was performed for 1 h at 120 V (constant) in a Bio-Rad miniature transfer apparatus.…”

The phosphatidylinositol/AKT/atypical PKC pathway is involved in the improved insulin sensitivity by DHEA in muscle and liver of rats in vivo

“…The supernatant was either used for immunoprecipitation with anti-IR, anti-IRS-1, anti-IRS-2 and protein A-Sepharose 6MB or treated as whole extract tissues with Laemmli sample buffer treatment and electrophoresis in SDS-PAGE as described elsewhere (Carvalho et al, 1996(Carvalho et al, , 1997. For whole tissue extracts, similar sized aliquots (200 Ag protein) were subjected to SDS-PAGE and immunoblotted with anti-phospho-AKT or anti-phospho-PKC antibodies.…”

Low ethanol consumption induces enhancement of insulin sensitivity in liver of normal rats

“…In fact, evidences that bradykinin stimulates the insulin signaling pathway were already reported (Isami et al, 1996) and its potential effect to enhance early steps of insulin signal in liver, after ACE inhibition, was also proposed (Carvalho et al, 1997). Furthermore, it was shown that the ethanol metabolite, acetaldehyde, inhibits ACE activity and might mediate systemic increase in bradykinin (Thevananther and Brecher, 1993).…”

“…A potential mechanism involves the renin-angiotensin-system (RAS) and bradykinin. It is known that angiotensin-converting enzyme (ACE) inhibition improves the in vivo insulin sensitivity (Carvalho et al, 1997;Prada et al, 2000) and it has been claimed that initial steps of insulin signaling are enhanced in rats treated with ACE inhibitor (Carvalho et al, 1997;Nawano et al, 1999). However, the block of the angiotensin receptor 1 with losartan had no similar effect, suggesting that the ACE inhibition effect does not involve the .…”

“…reduction of angiotensin II, but the parallel increase of bradykinin (Carvalho et al, 1997;Prada et al, 2000). In fact, evidences that bradykinin stimulates the insulin signaling pathway were already reported (Isami et al, 1996) and its potential effect to enhance early steps of insulin signal in liver, after ACE inhibition, was also proposed (Carvalho et al, 1997).…”