Amytal on Smooth Muscle.

Abstract

While using sodium amytal (sodium iso-amyl-ethyl barbiturate) as a routine laboratory anesthetic, it was observed that some of the dogs seemed to show certain signs of increased intestinal motility. Gruber 1 found the tone of isolated intestine, uterus and ureter diminished by the barbituric acid derivatives (uterus by 1:10,000 or stronger amytal solution). Drabkin et al. 2 reported maintenance of the rhythmic contractions and of response to the oxytocic principle of pituitary by the isolated uterus following large doses of amytal (1:1,000). 3 Swanson 4 obtained only a depression of the tone of all smooth muscle structures (by 1:25,000 sodium amytal or stronger).

As these observations are somewhat in conflict, a series of experiments was done with smooth muscle tissues from various animals. The animals were killed by exsanguination and the desired parts removed at once and placed in iced Tyrode's or Locke's solution, where they were kept 2-4 hours. (In one or two instances where ether had been used a longer cold waiting period was found to improve the behavior.) The physiological bath chamber contained 200 cc. Precautions were observed as to constancy of temperature, oxygenation and pH.

The first experiments showed only depression by sodium amytal. On using smaller and smaller doses of the drug, however, a consistent “reversal effect” was obtained with every specimen that offered a uniform and dependable activity. Concentrations of 1:100,000-1:40,000 caused a prompt and vigorous increase in tone, too often sending the writing point above the paper, although the lever magnification was only 3:1 and the segment a short one. This high tone was generally accompanied by an increase in the height of individual contractions. This rise was maintained for at least 30 minutes unless a change was made in the content of the bath.