One‐Time Acute Elevation of Muscle Temperature Is Effective for Attenuation of Exaggerated Exercise Pressor Reflex in Rats with Peripheral Artery Disease

Abstract

BackgroundThe blood pressure (BP) response is augmented during static exercise in peripheral artery disease (PAD). Heating treatment was found to be effective for the attenuation of the BP response in PAD patients. However the underlying mechanism for the muscle temperature (Tm) on BP responses in PAD is still unclear.AimsWe first determined the effect of one‐time acute Tm elevation on the exaggerated exercise pressor reflex in PAD rats with 72 hours of femoral artery occlusion. We further determined if P2X receptor was engaged during this process because a lower Tm in occluded muscle can alter expression and function of P2X.MethodsThe BP response to static muscle contraction was recorded to examine the exercise pressor reflex. Also, αβ‐methylene ATP (αβ‐me ATP) was injected into the arterial blood supply of the hindlimb muscles to stimulate P2X receptors in the muscle afferent nerves. To elevate the Tm, a heating pad was placed locally on the hindlimb and the Tm was increased by ~1.5 °C. Then the Tm was stabilized and maintained for 5 min.ResultsThe BP response to static muscle contraction was examined 20 minutes before (pre‐heat), immediately following (acute heat) and 20 minutes after the end of elevation of Tm (recovery). Compared with control rats, a greater mean arterial pressure (MAP) response was observed in PAD rats in the pre‐heat session (27.50±2.07 mmHg in PAD rats/n=12 vs. 18.00±1.67 mmHg in control rats/n=9; P<0.05). However, following elevation of the Tm, the amplification of MAP response was similar in PAD rats and in control rats (21.25±3.00 mmHg in PAD rats/n=12 vs. 18.00±2.56 mmHg in control rats/n=8; P>0.05). During the recovery, a greater MAP response remained in PAD rats (27.54±0.90 mmHg in PAD rats/n=11 vs. 20.14±1.43 mmHg in control rats/n=7; P<0.05). Note that no significant difference in developed muscle tension during contraction was seen in control rats and PAD rats (P>0.05). When αβ‐me ATP (0.125mM) was given, the MAP responses were higher in PAD rats (n=7) than in control rats (n=7) (56.03±4.70 mmHg in PAD vs. 39.12±4.59 mmHg in control for pre‐heat, 59.63±3.55 mmHg in PAD vs. 39.92±5.20 mmHg in control after heating, and 63.33±2.51 mmHg in PAD vs. 35.57±4.38 mmHg in control for recovery; P<0.05 for all sessions between two groups).ConclusionOne‐time acute elevation of the Tm inhibits the exaggeration of the exercise pressor reflex in PAD rats. The effects of one‐time heat may not be through alternating muscle afferent nerves’ P2X receptors.Support or Funding InformationThis study was supported by NIH P01 HL134609 & R01 HL141198