Capsaicin facilitates carotid sinus baroreceptor activity in anesthetized rats

To study the effect of capsaicin on carotid sinus baroreceptor activity (CBA).

The functional curve of carotid baroreceptor (FCCB) was constructed and the functional parameters of carotid sinus baroreceptor were measured by recording sinus nerve afferent discharge in anesthetized rats with perfused isolated carotid sinus.

Low-concentration of capsaicin (0.2 mumol/L) had no significant effect on CBA, while perfusion of the isolated carotid sinus with middle-concentration of capsaicin (1 mumol/L) could shift FCCB to the left and upward, with peak slope (PS) increased from (2.47 %+/-0.14 %)/mmHg to (2.88 %+/-0.10 %)/mmHg (P<0.05) and peak integral value of carotid sinus nerve discharge (PIV) enhanced from 211 %+/-5 % to 238 %+/-6 % (P<0.01). The threshold pressure (TP) and saturation pressure (SP) were significantly decreased from 68.0+/-1.1 to 62.7+/-1.0 mmHg (P<0.01) and from 171.0+/-1.6 to 165.0+/-0.6 mmHg (P<0.01). By perfusing with high-concentration of capsaicin (5 micromol/L), FCCB was shifted to the left and upward further and the changes of the functional parameters such as PS, TP, and SP were concentration-dependent. Pretreatment with ruthenium red (100 micromol/L), an antagonist of vanilloid receptor subtype 1 (VR1), blocked the effect of capsaicin on CBA. Preperfusion with glibenclamide (20 micromol/L), a K(ATP) channel blocker, could eliminate the effect of capsaicin on CBA.

Capsaicin exerts a facilitatory role on the isolated carotid baroreceptor in a concentration-dependent manner. The facilitatory action of capsaicin may be attributed to the opening of K(ATP) channels mediated by VR1.