Modification by baroreceptor feedback of circulatory responses to noxious stimuli during anaesthesia in cats

In eight cats anaesthetized with chloralose, the carotid sinus on one side was either exposed to systemic arterial pressure or perfused with a pump in order to control sinus pressure. Baroreceptor influences from the contralateral carotid sinus and from the aortic arch were interrupted by denervation. Arrangements were made for intermittent electric stimulation of pain fibres in somatic and visceral nerves with stimulation parameters chosen to elicit reproducible increases in arterial blood pressure and in skeletal muscle vascular resistance. The elicited increases in arterial pressure and muscle vascular resistance were both about 40% smaller when the carotid sinus was exposed to systemic arterial pressure in comparison with the experimental condition of a constant carotid sinus pressure. I.v. metoprolol (0.1-0.3 mg kg-1) reduced base-line arterial pressure, but did not attenuate the arterial blood pressure increase in response to pain stimulation. The baroreceptor modulation of the haemodynamic response to the pain stimulation was not affected by metoprolol.