The mechanisms involved in Baroreflex Activation Therapy (BAT) in patients with resistant hypertension require better understanding. It was shown that electrical stimulation of the carotid sinus (ESCS), in conscious carotid body-denervated rats, caused bradycardia and greater hypotensive response when compared with intact control rats. In the current study the activation of the chemoreceptors due to ESCS, in conscious rats, was examined in the absence of the carotid baroreceptors. Wistar rats with unilateral denervation of the right carotid chemoreceptors were divided into three groups: 1) control (CONT, n=7); 2) bilateral carotid chemoreceptor denervation (CD, n=7); 3) unilateral denervation of the left carotid baroreceptors (BD, n=4). Under ketamine/xylazine anesthesia bipolar electrodes were implanted around the left carotid sinus combined with arterial and venous catheters into the femoral vessels. On the next day, after basal hemodynamic recordings, the animals received three ESCS (5V, 1 ms) with 15 Hz, 30 Hz and 60 Hz, applied randomly for 20s. Carotid chemoreceptors denervation was confirmed by the lack of hemodynamic responses after the administration of KCN (40 μg iv). The efficacy of left carotid baroreceptor denervation was confirmed by the absence of hemodynamic responses to changes in the left carotid sinus pressure ranging from 60 mmHg to 180 mmHg. The results showed that ESCS was efficient to cause greater hypotensive responses in the CD as compared with the CONT group at 60 Hz (-37 ± 6 vs -19 ± 3 mmHg) and to cause hypertensive responses in the BD group at 30 Hz and 60 Hz (15 ± 2 and 19 ± 2 mmHg). ESCS caused no alteration of the heart rate in the CONT but caused significant bradycardia in the CD group at 30 Hz and 60 Hz (-31 ± 11 and -35 ± 12 bpm) and in the BD group at 15 Hz, 30 Hz and 60 Hz (-38 ± 6, -37 ± 6 and -34 ± 4 bpm). These data demonstrated that carotid chemoreceptor activation in the absence of the carotid baroreceptors caused hypertension and bradycardia, indicating that when the baroreceptors are intact, the chemoreceptors blunt the hypotensive response caused by ESCS. These findings provide important information for the clinical studies using BAT in patients with resistant hypertension and/or heart failure.
Pressor responses to electrical stimulation of the carotid sinus nerve in cats