Arterial and renal hemodynamics and baroreceptor function in normotensive and hypertensive rats during field stimulation of carotid baroreceptors

Objective: Field stimulation of the carotid baroreceptors has been used successfully to induce long-term reduction in blood pressure. However, the effect of baroreceptor stimulation on short-term blood pressure regulation and circulatory hemodynamics in normotensive and hypertensive rat models is not well established. Design and method: Male, Wistar Kyoto (WKY, n = 19) and spontaneously hypertensive rats (SHR, n = 19) (age: 13–58 weeks) were anaesthetised (urethane, 1.3 g/kg) and unilaterally vagotomised. Thoracic and aortic pressures, aortic pulse wave velocity (PWV), abdominal aortic flow and renal artery flow were measured. The left carotid artery was exposed and electrical field stimulation was applied to baroreceptors in the proximity of the carotid bifurcation (stimulation frequency: 100 Hz, pulse width: 0.53ms, signal amplitude: 3–5 v). A bolus of phenylephrine (1.5 μg) was delivered during baseline (no stimulation) conditions and during carotid baroreceptor stimulation to characterize baroreceptor function. Baroreceptor gain was computed as the absolute change in heart rate (HR) with respect to change in mean blood pressure (MAP). Results: Field stimulation caused a significant reduction (p < 0.001) in HR and MAP in both WKY and SHR, indicative of sympathetic inhibition. Mean aortic flow reduced significantly in SHR (p < 0.05) but did not change in WKY. However, mean renal flow decreased significantly in both WKY (p < 0.001) and SHR (p < 0.05). Pulse pressure showed a significant reduction in WKY (p < 0.05) as compared to SHR (p > 0.05). There was a significant reduction in PVW (p < 0.001) with stimulation in both WKY and SHR. There was no change in aortic or renal resistance. No change in baroreceptor gain (bpm/mmHg) was observed in both groups. WKY: gain (no stimulation), −0.54 ± 0.07; gain (stimulation), −0.48 ± 0.06. SHR: gain (no stimulation), −0.45 ± 0.07; gain (stimulation), −0.29 ± 0.03 mm/mmHg. There was a reduction in gain in SHR compared to WKY in both baseline (p > 0.05) and stimulation (p < 0.05) conditions. Conclusions: Unilateral field stimulation of carotid baroreceptor nerves reduced MAP, HR and mean renal flow in WKY and SHR while it preserved baroreflex function in both groups. There was a significant reduction in SHR baroreceptor gain compared to WKY during stimulation.