The Laxative Principle in Prunes

Abstract

No satisfactory study of the widely recognized cathartic effect of the French or Santa Clara variety of prune has ever been reported as far as we know. The purgative action appears in foodstuffs derived from prunes as well as in the dried prune itself. The apparent thermostability of the evacuant principle may be the factor leading Sollmann 1 and others to include prunes with the colloid and emollient laxatives which act “mainly by retaining water in the intestine by imbibition, thus modifying the bulk and consistency of the feces, so that these are more easily expelled.” Water-soluble substances in prunes have previously been held to play only a subsidiary role in catharsis; Sollmann 1 explains their action thus: “in fruits (prunes....., etc.) this colloid action is supported by the organic acids and sugars.”

We studied the cathartic efficacy of the soluble compounds present in dried prunes in an attempt to isolate the active substance responsible. Since such an active principle is present in very high dilution, routine chemical tests yield little information. The color reactions described by Tumin Katti and Beal, Fuller, Warren, and others 2 for anthraquinone derivatives which act through an irritant effect, are negative according to Mrak and Smith 3 for all prune extracts tested, indicating the absence of emodin-like compounds. The FeCl₃ test for phenolic groups is positive.

Three methods were used to evaluate the potency of various extracts. In spite of Sollmann's criticism 1 of the Magnus technique 4 with isolated gut, it is a convenient one to determine whether or not activity is present in materials tested. Preliminary tests were made by this technique on various prune preparations and the results so obtained were in accord with those found in intact animals by either Macht's 5 or Eddy's 6 method.

Actions of prune extracts on isolated rabbit, guinea pig, dog and cat jejunum or duodenum in either Sollmann and Rademaekers, 7 or Sollmann and von Oettingen's 8 solutions are summarized in Table I. The individual responses were confirmed at least in triplicate, and the tabulated results represent some 200 separate experiments. The water extracts were prepared according to the directions of Mrak and Cruess. 9 All other extracts were thoroughly freed of solvent by prolonged evaporation in vacuo and dissolved or suspended in water before being added to the bath. None of the extracts was sufficiently acidic or basic to influence the observed effect.

Summary. As tested by the techniques of Magnus, Macht, and Eddy, the laxative properties of prunes are not due entirely to colloidal or emollient effects in the intestine, as has been previously supposed, but would seem to depend also on the presence of an agent soluble in water, alcohol and pyridine. This active principle in prunes which is broken down by strong hydrolysis has otherwise certain chemical and physiological properties similar to di-hydroxy-phenyl isatin and to caffeic and chlorogenic acid.