Reflex Control of Blood Pressure and Heart Rate by Arterial Baroreceptors and by Cardiopulmonary Receptors in the Unanaesthetized Cat

Studies in unanaesthetized animals have reported that section of the carotid sinus and aortic nerves is accompanied by an increased blood pressure variability but not by a sustained blood pressure rise, thus questioning the role of arterial baroreceptors in the long term control of mean blood pressure values. However, sino-aortic denervation (SAD) does not produce denervation of all baroreceptor areas, and it has been suggested that aortic baroreceptor fibres in the vagus and cardiopulmonary vagal afferents that restrain sympathetic vasoconstrictor tone prevent blood pressure from permanently rising. In unanaesthetized cats we recorded blood pressure intra-arterially for 8-12 h when baroreflexes were intact, 7 days after SAD and 1-2 days after additional bilateral cervical vagotomy. Blood pressure signals were analysed by computer to provide means and coefficients of variation (CV, variabilities) for each recording period. In intact cats, mean blood pressure was 99 ± 7 mmHg (average ± s.e.) and CV 6 ± 1%. SAD did not alter mean blood pressure but markedly increased CV (12 ± 2%; P<0.01). Additional vagotomy did not alter mean blood pressure (104 ± 6 mmHg), nor did it alter the increased CV observed after SAD alone. Vagotomy failed to affect mean blood pressure and CV even when performed in cats with intact carotid and aortic nerves. The lack of effect of vagotomy did not depend on simultaneous section of afferent and efferent fibres, because selective blockade of the latter by atropine also failed to affect mean blood pressure and CV. These data show that neither arterial baroreceptors nor cardiopulmonary receptors have a prolonged effect on mean blood pressure and that not even a combined denervation of these reflexogenic areas can produce sustained blood pressure elevation. A prolonged effect of this denervation is a marked increase in blood pressure variability. This is exclusively due to arterial baroreceptor denervation, as cardiopulmonary receptors do not appear to exert any buffering action on blood pressure variability.