OBJECTIVETo investigate the effects of exhaustive exercise on contraction mediated by beta-adrenoceptor (beta-AR) in rat cardiac myocytes and to analyze the mechanism by which cardiac systolic dysfunction is caused after exhaustive exercise.

METHODSSixteen SD rats were divided randomly into sedentary group and trained group. Cardiac myocytes were isolated from sedentary group and trained group after five times of exhaustive exercise in one week. Shortening response to norepinephrine (NE), time-to-peak contraction (TTP) and time-to-95% relaxation (R95) were measured after alpha1-AR were blocked. Also shortening responses to different levels of NE were observed.

RESULTSShortening amplitudes in trained rat cardiomyocytes were lower than that in sedentary group. Compared with sedentary group, shortening amplitudes induced by beta-AR stimulation were significantly decreased, meanwhile TTPs and R95 were prolonged when beta-AR were activated in trained rat cardiomyocytes. beta-AR responsiveness to NE was weakened in trained group compared with that in sedentary group.

CONCLUSIONDecreased shortening cardiomyocyte systolic function stimulating by beta-AR could result in cardiac systolic dysfunction after exhaustive exercise.