Noradrenaline and cardiac hypertrophy in the rat: changes in morphology, blood pressure and ventricular performance.

Noradrenaline hydrochloride (160 micrograms base/kg per h) or vehicle were infused subcutaneously for 11 days into 35 male Wistar-Furth rats using osmotic minipumps. Chronic noradrenaline infusion produced moderate hypertrophy of both ventricles without causing tissue oedema. Left ventricular (LV) hypertrophy was concentric with no change in cavity volume, increased mass: volume ratio (approximately 50%) and increased fibre diameter (approximately 25%). In the conscious rat, noradrenaline produced only a slight increase in mean arterial pressure (13%) and heart rate (11%) but a marked increase in the variability of mean blood pressure (250%). The extent of LV hypertrophy was not related to the level of mean blood pressure or to its variability. In the anaesthetized rat, peak cardiac pumping ability was normal before and after cardiac autonomic blockade. Peak pressure-generating ability during aortic occlusion was increased in hypertrophied hearts before autonomic blockade but was similar to control rats after autonomic blockade. Chronic noradrenaline administration produces cardiac hypertrophy which has many similarities to hypertensive cardiac hypertrophy but no clear association with the level of blood pressure.