Effects of continuous field activation of carotid barorecptors on changes of arterial pressure in the rat

Background: Electric field activation of carotid baroreceptors is used for treatment of resistant hypertension. Although baroactivation is generally associated with reduction of blood pressure, there is, however, a marked variability in the response across individuals. The present study addresses the effect of baroactivation in a rat model in which blood pressure was modulated by pharmacological agents affecting peripheral resistance. Aim: To assess the effects of carotid baroactivation in the presence of pharmacologically induced changes in blood pressure. Methods: Male WKY rats (aged 12 weeks; n=6) were anesthetized (urethane, 1.3 g/kg) and implanted with a field stimulation electrode (1 kHz, pulse width of 0.53 ms) surrounding the common carotid artery, immediately proximal to the carotid bifurcation. Mean arterial pressure (MAP) was measured using two pressure sensors located in the proximal and distal descending aorta. Vasoactive agents (10 μg phenylephrine (PE) or 30 μg sodium nitroprusside (SNP), intravenous bolus) were used to alter MAP to quantify the induced changes in blood pressure before and during continuous field activation of carotid baroreceptors. Results: MAP decreased significantly with stimulation (14 ± 7.9 mmHg) accompanied by a simultaneous increase in heart rate (HR) (25 ± 6.2 bpm). These new baselines for MAP and HR were maintained during the entire stimulation period (30–60 minutes) with injection of vasoactive agents. The injection of PE and SNP caused significant (P<0.01) changes in MAP during stimulation (58 ± 12 mmHg and 26 ± 18 mmHg, respectively), as well as changes in HR (43 ± 29 bpm and 18 ± 8 bpm, respectively). These changes did not show any significant difference with injection of drugs in the absence of baroreceptor stimulation, showing that field activation of carotid baroreceptors does not reduce the capacity for cardiovagal control of blood pressure. Conclusion: The findings show a consistent decrease in arterial blood pressure during field activation of carotid baroreceptors in the presence of large pressure changes due to pharmacological manipulation of peripheral resistance. Another significant result was stability of baroreceptor sensitivity during stimulation.