Hemodynamics changes with acute carotid baroreceptor field stimulation are age-dependent in normotensive rats

Carotid baroreceptor stimulation can treat resistant hypertension with possible effects on the vasculature beyond the decrease in arterial pressure. This study aims to characterize age-dependency of vascular hemodynamics changes with unilateral field stimulation of carotid baroreceptors in normotensive rats to infer underlying hemodynamic mechanisms. Anesthetized Wistar-Kyoto rats divided into two groups (young: n=10, 13-33 weeks; old: n=6, 52-58 weeks) were instrumented to measure heart rate (HR) and mean arterial pressure (MAP), and flow in the abdominal aorta and renal artery. Measures of aortic and renal artery stiffness and resistance were calculated. Baroreceptor stimulation caused a consistent reduction in MAP, HR, pulse pressure and aortic pulse wave velocity. In young rats reduced MAP (77 +/- 10 to 64 +/- 13 mmHg, p<0.001) was concomitant with reduced mean aortic (40 +/- 15 to 32 +/- 11 ml/min, p<0.05) and renal flow (3.0 +/- 1.6 2.2 +/- 1.1 ml/min, p<0.001). However, in old rats reduced MAP (76 +/- 14 to 64 +/- 10 mmHg, p<0.05) occurred with a reduced aortic resistance (1.8 +/- 0.9 to 1.6 +/- 0.9 mmHg.min/ml, p<0.05), renal artery resistance (17.4 +/- 2.4 to 16.5 +/- 2.3 mmHg.min/ml, p<0.05) and mean renal flow (4.5 +/- 1.2 to 4.0 +/- 1.1 ml/min, p<0.05). This was consistent with reduced characteristic impedance in older rats in both the aorta (0.17 +/- 0.08 to 0.13 +/- 0.08 mmHg.min/ml, p<0.05) and renal artery (4.97 +/- 1.16 to 3.97 +/- 1.08 mmHg.min/ml, p<0.05). Stimulation caused a leftward shift in renal impedance phase frequency spectrum in both age groups indicating changes in wave reflection from the renal bed. Findings show that the reduction in MAP due to carotid barostimulation is associated with different hemodynamic mechanisms that depend on age.