Muscle mechanosensitive reflex is suppressed in the conscious condition: effect of anesthesia

Abstract

To test the hypothesis that a muscle mechanosensitive reflex is suppressed in the conscious condition, we examined the effect of anesthesia on the cardiovascular responses to passive mechanical stretch of the triceps surae muscle in six conscious cats. The triceps surae muscle was manually stretched for 30s by extending the hip and knee joints and subsequently by dorsiflexing the ankle joint; the lateral gastrocnemius muscle was lengthened by 19 ± 3 mm. Heart rate (HR) and mean arterial blood pressure (MAP) did not change significantly during passive stretch of the muscle in the conscious condition. At 10–40 min after intravenously administering sodium pentobarbital (20–25 mg/kg), the identical passive stretch of the triceps surae muscle was able to induce the cardiovascular responses; HR and MAP were increased by 14 ± 1 beats/min and 14 ± 1 mmHg, respectively. In contrast, vigorous stretching skin on the triceps surae muscle elicited no significant changes in HR and MAP in the anesthetized condition, indicating that if cutaneous nociceptors and/or mechanoreceptors might be activated by the skin stretch, pain‐induced reflex cardiovascular responses would be inhibited by anesthesia. We conclude that passive mechanical stretch of skeletal muscle is capable of evoking the reflex cardiovascular response, which is suppressed in the conscious condition but exaggerated by anesthesia. This study was supported by a Grant‐in‐Aid for Scientific Research (B) from the Japan Society for the Promotion of Science.