Acute deletion of arterial baroreceptor input in the conscious rabbit

We describe the use of a snare to denervate the carotid sinus in conscious rabbits whose other arterial baroreceptors had been denervated 8-14 days previously by surgical operation. Within 2 min of tightening the snare arterial blood pressure had risen from 81 +/- 2 to 119 +/- 5 mmHg, and heart rate had risen from 214 +/- 9 to 280 +/- 9 beats min-1. They remained at these high levels for 15 min but then fell, so that after 30 min blood pressure and heart rate were 103 +/- 9 mmHg and 265 +/- 8 beats min-1 respectively. They declined somewhat further, but irregularly, over the succeeding 7 days. The previously brisk baroreceptor-heart rate and carotid sinus reflexes were abolished by ensnaring the carotid sinus nerve, and remained absent over the succeeding 7 days. This method of deleting input from the arterial baroreceptors is not confounded by general anaesthesia or surgical injury, and allows observations to be made within minutes. The rapid decline in blood pressure and heart rate after 15 min, and the subsequent slow downward trend, are unexplained. They are of potential importance in experiments designed to quantitate the effects of baroreceptor input on the circulation. We also noted that, whereas spontaneous activities of the baroreceptor-intact rabbit were usually associated with transient rises of blood pressure and heart rate, after deletion of baroreceptor input the same activities were usually associated with transient falls.