AGE-RELATED EFFECTS OF NOREPINEPHRINE ON RAT VENTRICULAR HYPERTROPHY

Norepinephrine (NE) (2.5 mu g/kg/min) was administered to 5-week-old m ale Sprague Dawley rats by subcutaneous osmotic mini pumps for 14 days to generate an in vivo cardiac hypertrophy model and the responses wi th respect to aging examined. In the model, ventricles were significan tly hypertrophied without myocardial necrosis and without significant increases in heart rate or blood pressure; the beta adrenergic system was down-regulated. In 37-week-old rats receiving 1.0 mu g/kg/min NE, there was a tendency towards heart failure, and myocardial necrosis an d interstitial fibrosis were revealed by histological examinations. Th e density of beta adrenergic receptors and adenylyl cyclase activity w as lower in the older rats. The excess stimulation of adrenergic recep tors caused severe cardiac injury in old rats regardless of down regul ation of beta adrenergic receptors.