Rapid baroreceptor resetting is unaltered by chronic hypertension in rats

Abstract

This study compares rapid baroreceptor resetting in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Single-fiber baroreceptor activity and aortic diameter were measured in in vitro preparations. Baroreceptor pressure threshold (Pth) and suprathreshold pressure sensitivity were measured during periods after various levels of conditioning mean arterial pressure (cMAP). The ability of a baroreceptor to reset was expressed as the resetting ratio (delta Pth/delta cMAP). Rapid resetting was successfully characterized in 30 baroreceptors (18 SHR and 12 WKY). SHR blood pressures were higher, and aortic distensibility was lower than in WKY. SHR baroreceptors showed signs of chronic resetting, i.e., elevated Pth (105.4 vs. 88.5 mmHg, SHR and WKY, respectively) and decreased suprathreshold sensitivity (0.92 vs. 1.42 spikes.s.-1.mmHg-1, SHR and WKY, respectively), but their resetting ratios were similar to WKY (0.260 and 0.237, SHR and WKY, respectively). Characterization of rapid resetting of more than one baroreceptor from single animals reveals that the resetting ratio can vary by greater than 50% within animals. During simultaneous discharge-diameter recordings, the strain threshold was better correlated to cMAP than Pth. We conclude that the ability of baroreceptors to rapidly reset is unaltered by chronic hypertension or chronic baroreceptor resetting, and we hypothesize that rapid resetting is probably a result of an intrinsic neural property rather than vessel mechanics.