EFFECTS OF AMPHETAMINE AND COCAINE ON NEUROMUSCULAR FUNCTION

¹ Department of Pharmacology and Biochemistry, Catholic University of Chile, Santiago, Chile

Cats anesthetized with nembutal were used in studying the effect of amphetamine and of cocaine on action potentials of A fibers, on neuromuscular transmission and on muscular contractions. No important effect of amphetamine was observed upon the alpha waves of the A fibers.

Amphetamine has a de-fatiguing effect during low frequency stimulation. During high frequency direct or indirect stimulation (i.e., during intense activity of the contractile mechanism), the drug acted as a depressant.

The response of denervated muscles to acetylcholine was increased by amphetamine. The drug produced a contractile response in both normal and denervated skeletal muscles. Since this response was not accompanied by action potentials, it was a contracture.

Although amphetamine had a tachyphylactic effect on blood pressure, apparently it had none on muscular response.

During indirect muscular stimulation, cocaine acted to increase or decrease response. The same effect was produced when a denervated or fully curarized muscle was directly stimulated. The more tension developed by the muscle, the easier it was to demonstrate depression. Increased response seemed to be related to the development of contraction fatigue. Cocaine in small doses increased the response of denervated muscles stimulated by acetylcholine. With large doses a depression resulted.