Objectives Tanshinone IIA, one of the active ingredients in danshen, which derived from the dried root or rhizome of Salviae miltiorrhizae BGE, is cardioprotective when applied before myocardial sustained ischaemia. This study is to investigate the effect of pharmacological postconditioning with tanshinone IIA on attenuating myocardial ischaemia-reperfusion injury when applied after myocardial sustained ischaemia, and the potential mechanism involved in it.
Methods Eighty Sprague-Dawley rats, receiving 30 min ischaemia and 5 min or 120 min reperfusion, were randomly divided into 6 groups: the sham group without ischaemia (Sham) (n = 8); the control group without other intervention (Control) (n = 16); the ischaemic postconditioning group (Post) (n = 16), given 3 cycles of 10 s reperfusion and 10 s ischaemia before reperfusion; the low-dose and high-dose tanshinone IIA treatment group (Tan-L, n = 16, and Tan-H, n = 8, respectively), given an injection of 10 mg/Kg or 20 mg/Kg tanshinoe during 25-30 min ischaemia; the low-dose tanshinone IIA plus a specific inhibitor of phosphatidylinositol 3-kinase (PI3K/Akt), LY294002 group (Tan + LY) (n = 16), with an additional injection of PI3K inhibitor (LY294002) 0.3mg/kg in external jugular vein slowly 15 min before reperfusion. Myocardial infarct size were detected by triphenyltetrazolium chloride, mitochondrial permeability transition (MPT) by spectrophotometry, and the contents of phospho-Akt (p-Akt) and phospho-eNOS (p-eNOS) in myocardium by Western blot.
Results Compared with the Control group, the Post, Tan-L and Tan-H groups had smaller infarct size (46.9% ± 3.6% vs. 25.3% ± 4.3%, 29.2% ± 4.5%, 28.5 ± 3.0%, P < 0.01), without difference among Post, Tan-L and Tan-H groups. The Post and Tan-L groups had less reduction in optical density at 540 nm (OD540) for MPT, and greater p-Akt and p-eNOS protein expression than the Control group (p-Akt/t-Akt: 2.3 ± 0.3, 2.2 ± 0.3 vs. 1.0 ± 0.0, P < 0.01; p-eNOS/t-eNOS: 2.1 ± 0.2, 1.8 ± 0.2, vs. 1.0 ± 0.0, P < 0.01, respectively). The Tan-L-induced cardioprotection and inhibition of MPT were abrogated completely by LY294002 (P < 0.01).
Conclusions Pharmacological postconditioning with tanshinone IIA may protect myocardium from ischaemia-reperfusion injury through PI3K-Akt-eNOS pathway, and the inhibition of MPT may be involved in this protection effect.