Arterial blood pressure control during hindlimb and forelimb contraction in the dog.
This study examined the differential reflex cardiovascular responses evoked by separate contractions of the right hindlimb and forelimb and established the mechanism of a regional reflex vasodilation associated with hindlimb skeletal muscle contraction. The two groups of skeletal muscle were contracted separately by electrical stimulation (2-48 Hz) of the peripheral motor nerves. The left nonexercising hindlimb was perfused at constant flow. All blood pressure-regulating mechanisms were intact. Arterial blood pressure (ABP), left nonexercising hindlimb perfusion pressure (HLPP), and heart rate (HR) were recorded. HR was increased by skeletal muscle contraction. This response was independent of muscle group and contraction frequency. Increases in both ABP and HLPP were produced by high-frequency contractions (greater than 16 Hz) of either the hindlimb or forelimb. Decreases were evoked only by hindlimb contractions (greater than 8 Hz). The nonexercising skeletal muscle vascular bed contributed to this systemic depressor response by vasodilating. The mechanism involved a contraction-induced withdrawal of sympathetic nerve activity to that vascular bed. Concomitant with this response was an increase in heart rate that was blocked with propranolol. Similar heart rate changes evoked by forelimb contractions also were blocked with propranolol. These data indicate that sympathetic outflow to resting skeletal muscle depends on the origin and magnitude of the afferent signal from the contracting skeletal muscle.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001794:Blood Pressure; D002320:Cardiovascular Physiological Phenomena; D004285:Dogs; D004558:Electric Stimulation; D005121:Extremities / Q000098:blood supply; D006339:Heart Rate / Q000187:drug effects; D009119:Muscle Contraction; D010646:Phentolamine / Q000494:pharmacology; D005082:Physical Exertion; D011433:Propranolol / Q000494:pharmacology; D012018:Reflex / Q000502:physiology
D001285:Atropine; D011433:Propranolol; D010646:Phentolamine