The effects of testosterone on norepinephrine release were investigated in the isolated rat hearts.Sprague-Dawley male rats (n=120) were randomized to testosterone and control groups.The rats in testosterone group were perfused with modified Krebs-Henseleit buffer containing different concentrations of testosterone (0.1,1.0,10.0,and 100.0 nmol/L,respectively).Myocardial ischemia was induced by globally stopping the perfusion flow.Exocytotic norepinephrine release was induced by electrical field stimulation at 5 V (effective voltage) and 6 Hz (pulse width of 2 ms) for 1 min.The overflow of norepinephrine was determined by high pressure liquid chromatography and electrochemical detection (HPLC-EC).Following acute ischemia,testosterone (1.0,10.0 and 100.0 nmol/L) significantly reduced norepinephrine release (P＜0.01),and the norepinepherine overflow was similar between the control and 0.1 nmol/L testosterone group (P＞0.05).Electrical stimulation of the ventricle evoked norepinepherine release,and this was diminished by the perfusion with testosterone at the concentrations of 1.0,10.0 and 100.0 nmol/L (P＜0.01).It is suggested that testosterone suppresses ischemia- and electrical stimulation-induced norepinepherine release in the isolated rat hearts.