Effects of testosterone on norepinephrine release in isolated rat heart

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.