Influence of Histamine and Acetylcholine on Nerve Block due to Procaine

Abstract

IN a previous communication¹, experiments on nerve-muscle preparations were reported, showing that histamine is able to restore conduction in a nerve, blocked by procaine, even though procaine is still present. These experiments have now been confirmed by action potential studies. In a typical experiment the central part of a frog ischiadicus nerve, from which the connective tissue sheath had been carefully removed, was placed in a phosphate Ringer solution containing 0.05 per cent procaine hydrochloride. The solution was adjusted to pH. 7.3 in the presence of 6.5 per cent carbon dioxide. The nerve was stimulated with a break shock every second, and every spike was photographed. Total block occurred after 9.6 min. Then, without moving the nerve from the electrodes, this solution was replaced by a similar solution, containing 0.05 per cent procaine hydrochloride and 0.5 per cent histamine dihydrochloride, also adjusted to pH. 7.3. Recovery began almost immediately, and in 1.9 min. the spike area was 72 per cent of the value at the onset of the experiment. This seemed to be the maximal effect.