Studies in neuromuscular transmission. III. Influence of changes in blood pH and carbon dioxide tension on the effect of tubocurarine and dimethyl tubocurarine.

Abstract

The influence of changes in pH and the partial pressure of carbon dioxide in arterial blood on the neuromuscular blocking effect of a single dose of tubocurarine or dimethyl tubocurarine was investigated in rabbits. The sciatic nerve was stimulated supramaximally at a rate of 3 per second and the electrical response of the gastrocnemius muscle was recorded; the amplitude of the first and fourth response was measured. During the period of spontaneously subsiding block after a single injection of the blocking agent, a shift in the arterial pH was produced either with or without a change in carbon dioxide tension. An increase of the block during this period was always considered significant but a decrease of the block only if it was followed by a spontaenous increase. The action of tubocurarine increased during acidosis and diminished during alkalosis. This effect was greater during metabolic alkalosis and acidosis, corresponding to a more rapid shift in pH, than during respiratory alkalosis and acidosis, but no qualitative difference was observed. The effect of a shift in pH is explained by changes in the potency of tubocurarine. The action of dimethyl tubocurarine was not influenced by changes in pH or carbon dioxide tension.