Continuous and intermittent electrical stimulation of the aortic depressor nerve in conscious rats: time course of the hemodynamic responses

Abstract

We investigated the time course of the hemodynamic responses to continuous (CONT) or intermittent (ON/OFF) electrical stimulation of the aortic depressor nerve (ADN) in conscious rats. Rats were implanted with electrodes around the ADN and a catheter into the femoral artery. On the next day the baseline systolic (SAP), diastolic (DAP), mean arterial pressure (MAP) and heart rate (HR) were recorded during 30 minutes and the rats were randomly assigned to CONT (0.5 mA; 0.25 ms; 30 Hz) or ON/OFF (5s ON/3s OFF; 0.5 mA; 0.25 ms; 30 Hz;) stimulation during 60 min. Changes were greater under CONT as compared to ON/OFF stimulation (SAP: −21 ± 4 vs −10 ± 2 %; DAP: −23 ± 4 vs −14 ± 3 %; MAP: −22 ± 4 vs −12 ± 3 %). In addition, under CONT stimulation the HR was reduced within the first 5 min. The hypotensive and bradycardic responses were maintained over the entire period of stimulation in the ON/OFF protocol. Nevertheless, as compared to the first 5 min, CONT stimulation showed a rapid transitory increase in DAP (72 ± 3 vs 64 ± 3 mmHg) and MAP (87 ± 3 vs 78 ± 4 mmHg). In conclusion, CONT stimulation of the ADN elicits greater hemodynamic responses as compared to the ON/OFF protocol. This finding indicates that the CONT stimulation is more effective to reduce the arterial pressure during long period of electric baroreflex activation.Financial support: FAPESP, CNPq and CAPES.