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Activation of phosphoinositide-3 kinase (PI3K) is essential for cell growth, relating to adaptive and maladaptive cardiac hypertrophy. This longitudinal canine study was designed to investigate the role of PI3Kα and PI3Kγ in cardiac remodelling during congestive heart failure (CHF) and cardiac recovery (CR).All dogs were surgically instrumented. Congestive heart failure was induced by cardiac pacing for 3–4 weeks and CR was allowed by terminating pacing for 5–6 weeks after induction of HF. Control dogs had sham surgery, but did not undergo pacing. Left ventricular (LV) contractile function was depressed in CHF and restored to 80–90% of the normal level in CR, with a 25% increase in LV weight. The expression of PI3Kγ was increased four-fold in CHF, but returned to control levels in CR. In contrast, the expression of PI3Kα in CHF was not different from that in controls, but increased three-fold in CR and was accompanied by increases in phosphorylation of Akt (five-fold), GSK-3β (five-fold), β-catenin (three-fold), mTOR (two-fold), and P70S6K (two-fold).Our results indicate that PI3K isoforms are regulated differently during the course of CHF/CR and that the selective activation of PI3Kα, through Akt, GSK-3β, and mTOR signalling pathways, may be involved in the development of cardiac compensatory hypertrophy and functional restoration.