ANGIOTENSIN-II INDUCES TYROSINE PHOSPHORYLATION OF INSULIN-RECEPTOR SUBSTRATE-1 AND ITS ASSOCIATION WITH PHOSPHATIDYLINOSITOL 3-KINASE IN RAT-HEART

We have investigated whether angiotensin II (AII) is able to induce in sulin receptor substrate 1 (IRS-1) phosphorylation and its association with phosphatidylinositol 3-kinase (PI 3-kinase) in the rat heart in vivo. The phosphorylation state of IRS-1 following infusion of insulin or AII via the vena cava was assessed after immunoprecipitation with an anti-peptide antibody to IRS-1 followed by immunoblotting with an a nti-phosphotyrosine antibody and an anti-PI 3-kinase antibody. Densito metry indicated a 5.6 +/- 1.3-fold increase in IRS-1 phosphorylation a fter stimulation with AII and a 12.8 +/- 3.1-fold increase after insul in. The effect was maximal at an AII concentration of 10(-8) M and ocu rred 1 min after infusion. There was also a 6.1 +/- 1.2-fold increase in IRS-1-associated PI 3-kinase in response to AII. In the isolated pe rfused heart the result was similar, showing a direct effect of AII on this pathway. When the animals were pretreated for 1 h with DuP 753, a non-peptide AII-receptor 1 (AT1 receptor) antagonist, there was a ma rked reduction in the AII-induced tyrosine phosphorylation of IRS-1, s uggesting that phosphorylation is initially mediated by the ATI recept or. We conclude that An stimulates tyrosine phosphorylation of IRS-1 a nd its association with PI 3-kinase. This pathway thus represents an a dditional signalling mechanism stimulated by AII in the rat heart in v ivo.