Dynamic characteristics of baroreflex neural and peripheral arcs are preserved in spontaneously hypertensive rats

Although baroreceptors are known to reset to operate in a higher pressure range in spontaneously hypertensive rats (SHR), the total profile of dynamic arterial pressure (AP) regulation remains to be clarified. We estimated open-loop transfer functions of the carotid sinus baroreflex in SHR and Wistar Kyoto (WKY) rats. Mean input pressures were set at 120 (WKY120 and SHR120) and 160 mmHg (SHR160). The neural arc transfer function from carotid sinus pressure to efferent splanchnic sympathetic nerve activity (SNA) revealed derivative characteristics in both WKY and SHR. The slope of dynamic gain (in decibels per decade) between 0.1 and 1 Hz was not different between WKY120 (10.1 ± 1.0) and SHR ₁₂₀ (10.4 ± 1.1) but was significantly greater in SHR ₁₆₀ (13.2 ± 0.8, P < 0.05 with Bonferroni correction) than in SHR ₁₂₀. The peripheral arc transfer function from SNA to AP showed low-pass characteristics. The slope of dynamic gain (in decibels per decade) did not differ between WKY ₁₂₀ (-34.0 ± 1.2) and SHR ₁₂₀ (-31.4 ± 1.0) or between SHR ₁₂₀ and SHR ₁₆₀ (-32.8 ± 1.3). The total baroreflex showed low-pass characteristics and the dynamic gain at 0.01 Hz did not differ between WKY ₁₂₀ (0.91 ± 0.08) and SHR ₁₂₀ (0.84 ± 0.13) or between SHR ₁₂₀ and SHR ₁₆₀ (0.83 ± 0.11). In both WKY and SHR, the declining slope of dynamic gain was significantly gentler for the total baroreflex than for the peripheral arc, suggesting improved dynamic AP response in the total baroreflex. In conclusion, the dynamic characteristics of AP regulation by the carotid sinus baroreflex were well preserved in SHR despite significantly higher mean AP.