THE RESPONSE OF THE TRICEPS SURAE OF NORMAL, ADRENALECTOMIZED, DESOXYCORTICOSTERONE ACETATE-TREATED AND KCl-TREATED RATS TO DIRECT AND INDIRECT, SINGLE AND REPETITIVE STIMULATION

Abstract

Single direct stimuli in the rested muscle of adrenalectomized rats produced responses with a higher tension than those found in normal muscle similarly stimulated. Curarization did not alter the time course of isometric responses to single direct stimuli in normal muscle but it reduced the peak tension and rising time of responses to similar stimulation in muscle of adrenalectomized rats to values approximately equal to those for normal muscle. This effect of curare suggests that responses obtained from uncurarized adrenalectomized animals involve repetitive contraction. Post-tetanic potentiation was not impaired by complete curarization. It is concluded that increased contractile strength of muscle fibers rather than repetitive contraction or recruitment of muscle fibers is responsible for the potentiating effect of tetanus. Greater KC1 potentiation of muscle response was obtained during indirect stimulation than during direct stimulation of curarized muscle. The marked exaggeration of rising time and peak tension during the first few muscle responses to single indirect stimuli in desoxycorticosterone acetate (DCA)-treated rats is indicative of prolonged repetition. The maximal tetanic tension produced by direct stimulation was only slightly impaired by adrenalectomy. After adrenalectomy, neuromuscular transmission at high frequency (225/sec.) as well as at low (2/sec.) is at least as good as normal. The Wedensky inhibition manifest in normal rats at high frequency of indirect stimulation was exaggerated by DCA treatment. KC1 treatment diminished Wedensky inhibition in normal and in DCA-treated animals.