Objective: To observe the protective effect and of pretreatment with glycyrrhizic acid on myocardial ischemia reperfusion injury (MIRI) in rats and expressions of B-cell lymphoma/leukemia-2 (Bcl-2) and Bcl-2 associated X protein (Bax).Method: Fifty SD rats were randomly divided into sham operation group (Sham group)

myocardial ischemia-reperfusion injury group (MIRI group)

low-dose group

middle-dose group

and high-dose group. The myocardium ischemia reperfusion injury model in rats was established through ligation of the left anterior descending of the coronary artery. Rats in Sham group were not ligated after threading. Rats in MIRI group were administered with saline at the dose of 2 mg · kg-1 through intraperitoneal injection 30 minutes before ischemia. Low-dose group

middle-dose group and high-dose group were administered with glycyrrhizic acid at doses of 2

4 and 10 mg · kg-1 through intraperitoneal injection 30 minutes before ischemia. The pathological histologic changes in myocardial tissues were observed under optical microscope. Creatine kinase isoenzyme (CK-MB) activity

lactate dehydrogenase (LDH) activity

cardiac troponin-T (cTnT)

tumor necrosis factor-α (TNF-α)

interleukin-6 (IL-6)

myeloperoxidase (MPO) activity

superoxide dismutase (SOD) activity

glutathione peroxidase (GSH-Px) activity and malondialdehyde (MDA) were detected. Apoptotic index of myocardial cells was detected by terminal dexynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL)

and expressions of Bcl-2 and Bax in cardiac muscle tissues were detected by Western blot.Result: Compared with MIRI group

myocardial ischemia reperfusion injury in rats was reduced significantly in low-dose group

middle-dose group and high-dose group. Compared with MIRI group

CK-MB activity

LDH activity

cTnT

TNF-α

IL-6

MPO activity and MDA were significantly reduced in low-dose group

middle-dose group and high-dose group (P<0.05

P<0.01)

while SOD activity and GSH-Px activity were significantly elevated in low-dose group

middle-dose group and high-dose group (P<0.05

P<0.01). Compared with MIRI group

apoptotic index of myocardial cells was significantly reduced in low-dose group

middle-dose group and high-dose group (P<0.01). Compared with MIRI group

expression of Bcl-2 in cardiac muscle tissues and ratio of Bcl-2

Bax were significantly elevated in low-dose group

middle-dose group and high-dose group (P<0.05

P<0.01)

while expression of Bax in cardiac muscle tissues was significantly reduced in low-dose group

middle-dose group and high-dose group (P<0.01).Conclusion: Glycyrrhizic acid has a protective effect on myocardial ischemia reperfusion injury in rats by inhibiting apoptosis of myocardial cells

and can elevate expression of Bcl-2 and reduce expression of Bax in cardiac muscle tissues.