OBJECTIVETo investigate the cardiac effect of interleukin-2 (IL-2) and to explore the underlying mechanism.

METHODSThe video tracking system and spectrofluorometric method were used to measure the cell contraction and intracellular calcium. Fura-2/AM was used as a calcium fluorescence probe. Langendorff perfusion technique was used to determine the effect of IL-2 on the intact heart.

RESULTSCompared with the control group, IL-2 5 U/ml, 50 U/ml significantly decreased cell contraction amplitude [(74.95+/-4.79) vs (98.09+/-5.02)%, (64.30+/-5.24) vs (97.38+/-4.05)%], peak velocity of cell shortening [(70.23+/-4.85)% vs (98.09+/-5.46)%, (61.15+/-5.20)% vs (97.38+/-6.85)%], peak velocity of cell relengthening [(71.22+/-4.79)% vs (98.32+/-6.08)%, (68.16+/-5.24)% vs (97.55+/-5.00)%] and end- diastolic cell length [(88.28+/-5.84)% vs (97.95+/-5.52)%, (84.18+/-6.52)% vs (98.94+/-6.76)%]. IL-2 (5 U/ml, 50 U/ml) also markedly inhibited intracellular calcium transient [(74.94+/-4.90)% vs (98.09+/-3.74)%,(71.00+/-5.28)% vs (97.38+/-5.52)%], and elevated end-diastolic calcium level of ventricular myocytes [(113.91+/-5.93)% vs (100.10+/-3.02)%, (119.09+/-7.12)% vs (100.52+/-6.00)%], which were attenuated by the opioid receptor antagonist naloxone (Nal,10 nmol/L). In the isolated perfused rat heart,when compared with the control group, IL-2 50 U/ml markedly decreased left ventricular developed pressure [(79.91+/-2.18) vs (93.84+/-2.94)mmHg], maximal rate of rise of left ventricular pressure [(2370.7358.29) vs (2591.50+/-62.81)mmHg] maximal rate of fall of left ventricular [-(1460.95+/-38.6) vs -(1634.24+/-54.05) mmHg/s] and heart rate [(217.35+/-10.56) vs (244.52+/-11.23) beats/min], but increased left ventricular end-diastolic pressure (11.44+/-1.02 vs 9.23+/-0.46). Pretreatment with Nal (10 nmol/L) antagonized the cardiac depression and left ventricular end-diastolic pressure elevation induced by IL-2.

CONCLUSIONThe cardiac effect of IL-2 is mediated by opioid receptors on the membrane of cardiomyocytes.