Role of the autonomic nervous system in the control of heart rate and blood pressure in the defence reaction in conscious XXXX .

@entity2997 @entity101 @entity235 @entity591 @entity551
The present study was performed on conscious, chronically instrumented @entity235 , which underwent selective blockade of sympathetic adrenergic and vagal outflows. Excitements were performed on these animals in normal states (N), after chronic treatment with @entity2997 , for sympathetic blockade (SB), after cold vagal blockade (VB), and after combined sympathetic and vagal blockade (SB + VB). Heart rate and arterial blood pressure were monitored in all the experiments, while a group of @entity235 was also tested with an electromagnetic flowmeter on the superior mesenteric artery. The role of the sympathetic and parasympathetic controls in the defence reaction was assumed from comparison of experiments performed in the presence or in the absence of each (or both) autonomic component(s). In the SB + VB condition, excitement was followed by @entity551 , without changes in heart rate. In VB experiments, a brief and transient @entity551 appeared, followed by gradually developed @entity101 , while heart rate progressively rose in about 5 s; there was no sudden increase in mesenteric vascular resistance, which contrasted with the very marked reaction in N experiments. Under vagal control alone (SB), the stimulus elicited prompt @entity591 and @entity101 , followed by a period of moderately reduced blood pressure. We conclude that, while the defence reaction leads to a @entity551 , in the absence of compensatory mechanisms, both branches of the autonomic nervous system play a protective role against @entity551 . In addition, the modulation of the vagal outflow, leading to sudden changes in the heart performance, seems to be responsible for the initiation of the overall haemodynamic adjustments following excitements. The possibility that withdrawal of the parasympathetic outflow to the heart may raise arterial blood pressure was verified in a special experiment in which artificial vagal stimulation in a conscious (vagal blocked) @entity235 , was turned off for brief periods, before and after @entity2997 . This led to changes in blood pressure and heart rate very similar to those seen at the onset of the defence reaction, both in N and SB conditions.
