Actions of ricinoleic acid and structurally related fatty acids of the gastrointestinal tract. I. Effects on smooth muscle contractility in vitro.

Ricinoleic acid and several structurally related compounds were tested for their effects on the smooth muscle contractions of the coaxially stimulated guinea-pig ileum, the spontaneously contracting rabbit jejunum, 90 mM potassium depolarized guinea-pig taenia coli and rat colon. In concentrations of 1.25 X 10(-5) to 4 X 10(-4) M, ricinoleate produced a dose-dependent depression of the stimulated guinea-pig ileum. This action was not produced by matching concentrations of oleate, elaidate, linoleate, 12-hydroxystearic acid, 10(9)-hydroxystearate, the methyl ester of ricinoleic acid or the trans isomer, recinelaidate. The alcohol derivative, ricinoleyl alcohol, was active and, although the depression produced by it took longer to maximize, the dose-response curves for ricinoleate and ricinoleyl alcohol on this tissue were almost superimposable. Ricinoleate showed the same qualitative and quantitative effects on the spontaneously contracting rabbit jejunum, but several differences were noted on the depolarized preparations. Ricinoleate-induced depression of depolarized smooth muscle was much slower in onset and required about 10 times higher concentrations to achieve equivalent responses. The results show that ricinoleic acid, the active ingredient in castor oil, is not a stimulant or irritant to isolated intestinal smooth muscle.