Effect of Propranolol on Monosynaptic Reflex Activity during a Task

Abstract

20 normal healthy subjects in a double-blind crossover experiment were given a tablet of either 40 mg propranolol or placebo half an hour before the beginning of the experiment. At rest and during the performance of a task, heart rate, Achilles tendon (T) and Hoffmann (H) reflexes were recorded. No increase in heart rate occurred during the task in the propranolol session. The increase of T-reflex amplitude, a common finding during the task under consideration, was larger in the propranolol session. No difference with H reflexes was found. It is concluded that the increase of T-reflex amplitudes during the task is caused only by fusimotor and not by sympathetic activity. It is speculated that if the sympathetic system plays a role at all, the effect on the T reflex is depressive rather than facilitating.

Activation of carotid baroreceptors inhibits spinal reflexes in man

“…could speculate that PRES induced heart rate deceleration leads to reflex inhibition. However, the results of the propranolol study (Brunia 1979) indicate that heart rate decrease can be accompanied by reflex increases.…”

“…A reduction of spinal reflex amplitudes is generally obselVed during sleep (Hodes and Dement 1964). Brunia (1979) used propranolol to investigate the sympathetic influence on muscle spindles. Compared to rest periods before and after mental arithmetic, heart rate and T reflex amplitude increased during the task in subjects under placebo.…”