SULFITE SUPPRESSES TRANSDUCER FUNCTION OF THE CAROTID-SINUS BARORECEPTOR

The purpose of this study was to examine the effect of sodium metabisu lfite (MBS) solution on the transducer function of the carotid sinus b aroreceptor. In anesthetized dogs with vagotomy, we vascularly isolate d the carotid bifurcation to load a pressure on the carotid sinus baro receptor. As the pressure load, we used a slow ramp increase (0.7 mmHg /s) in intracarotid sinus pressure (ICSP). The response of carotid sin us nerve activity (CSNA) to the slow ramp increase in ICSP was suppres sed when the isolated carotid sinus was filled with the MBS solution o f 10(-2) M. This suppressive effect of MBS solution on the response of CSNA was reversible. The MBS solution had no effect on the pressure-v olume relationship of the arterial wall of the isolated carotid sinus and on the impulse conduction of carotid sinus nerve. This suppressive effect of the MBS solution of 10(-2) M was weakened by introducing ox ygen gas into the solution to lose the total sulfite anions in the sol ution. These results suggest that: (1) the MBS solution reversibly sup presses the transducer function of the carotid sinus baroreceptor; (2) the target construction of the carotid sinus region that was affected by the MBS solution might be the carotid sinus baroreceptor nerve ter minal where ICSP was transduced into carotid sinus nerve firing; and ( 3) the suppressive effect might be provoked by the sulfite anions in t he MBS solution.