Effects of Gonadectomy, Testosterone Replacement and Supple- mentation on Cardiac Action Potentials in the Rat

The aim of this study was to evaluate the electro-physiological alterations induced by gonadectomy, testosterone replacement and supplementation on cardiac action potentials (APs) in sexually mature male rats. Furthermore we studied the effects of testosterone deprivation and administration on total protein (TPC) and sialic acid content (SAC) of the left ventricle. Four groups of rats were compared: control (C), gonadectomized (GD), GD replaced with testosterone propionate (5 mg/kg i.m. 6 days/week for 4 weeks, GDTP) and testosterone supplemented rats (TP 5 mg/kg i.m. 6 days/week for 4 weeks). The APs recorded from GD rats both in vitro on right ventricle papillary muscles, at various stimulation rates, and in situ in subepicardial cells, at spontaneous heart rate, showed a significant lengthening of action potential duration (APD) measured at 10% (APD10) and 50% (APD50) of repolarization in comparison with TP, GDTP and C. A significant lengthening of the finale phase of relaxation (APD95) was found also in TP rats. GD rats also showed a significant decrease in SAC. Testosterone replacement prevented both AP lengthening and SAC loss, whereas testosterone overload was associated only with a slight not significant increase of SAC. The rate at which ventricular fibrillation arises were determined and found to be lowered in both GD and TP groups when compared with C and GDTP rats. In conclusion, optimal testosterone serum level may contribute in the maintenance of normal myocardial electrogenesis and this may be partially attributed to regulation of the glycoprotein synthesis of glycocalyx.