RESUMEN
Male Wistar rats were decerebrated at precollicular level, by aspiration, under ether anaesthesia. The experiments employed rats instrumented for chronic electrocardiogram (ECG) recordings or mean blood pressure (MBP) and heart rate (HR) determination. Immediately after surgery, decerebrate (D) and sham operated (SO) animals presented a small and similar increase in their HR. Three and a half hours after surgery, SO group presented a normal HR, whilst D animals continued to show an increase in their HR up to 4.5 h, when it stabilized. Twenty four hours after surgery both groups presented similar MBP (D:110 +/- 6; SO:108 +/- 1 mmHg) but displayed marked differences on their HR (D:550 +/- 11; SO:335 +/- 5 beats/min). The blockade of parasympathetic tonus induced significant increases in the HR of both groups, without major changes in their MBP. Beta-adrenergic blockade reduced HR of both groups, bringing HR of D almost to control level. Simultaneously there was a reduction in MBP of D but not of SO animals. When parasympathetic blockade was superimposed to beta-adrenergic blockade, there was a significant increase in HR of SO, but not of D or in MBP of both groups. Thus we conclude that the decerebrate rat presents normal MBP with simultaneous tachycardia mainly caused by increased sympathetic outflow to the heart.