Effects of cholesterol on smooth muscle of intestine and uterus.

Abstract

In connection with a study of agents and conditions that may alter the responses of smooth muscle toward autonomic drugs, etc., it has been found that cholesterol definitely increases the activity of excised intestines and uteri of cats and rabbits. The results with flaky emulsions, and filtrates from saturated solutions, of the cholesterol in Tyrode's solution at 37° C. were the same. The exact concentration of the cholesterol in solution was unknown, quantitative estimation yielding only traces of the product, but a rough estimate indicated that muscular stimulation was secured with concentrations probably as low as 1:5,000,000. About the only important change conferred on the Tyrode solution by cholesterol was a lowering of surface tension.

The stimulation of intestinal and uterine muscle was essentially the same, being characterized by a prompt increase in the amplitude of contractions without material changes in rate and tonus in the majority of strips (Figure 1). In a small proportion of strips the rate of contraction and tonus were also increased. When the activity of muscles was weak at the start, or reduced by fatigue, it was almost invariably increased upon the direct addition of cholesterol to the bath. Duration of stimulation has been observed for as long as 30 minutes. Since the stimulation persisted after nicotinization and atropinization of intestiae, and was obtained with uteri whether inhibited or augmented by epinephrine, and was promptly opposed by papaverine, it was due to increase in contractility of the muscle substance independently of nerve endings and ganglia. Apocodeine (intestine) and ergotoxine (uterus), as a rule, abolished or prevented the action of cholesterol; but after these drugs the muscles were poisoned, as they were not responsive to barium.