Pharmacological Basis for the Medicinal Use of Psyllium Husk (Ispaghula) in Constipation and Diarrhea

The objective of this study was to determine the pharmacological basis of the medicinal use of psyllium husk (Ispaghula) in gastrointestinal motility disorders.

In-vivo studies were conducted on mice, and isolated rabbit jejunum and guinea-pig ileum were used in in-vitro experiments.

The crude extract of Ispaghula (Po.Cr) had a laxative effect in mice at 100 and 300 mg/kg, which was partially sensitive to atropine or SB203186 (5-HT₄ antagonist). At higher doses (500 and 1,000 mg/kg), Po.Cr had antisecretory and antidiarrheal activity. In guinea-pig ileum, Po.Cr (1–10 mg/ml) had a stimulatory effect, which was partially sensitive to atropine or SB203186. In rabbit jejunum, Po.Cr had a partially atropine-sensitive stimulatory effect followed by relaxation at 10 mg/ml. The relaxation was inhibited by the presence of l-NAME, a nitric oxide (NO) synthase inhibitor, or methylene blue, a guanylyl cyclase inhibitor. Similarly, the relaxant effect of Po.Cr on K⁺ (80 mM)-induced contractions, was attenuated in the presence of l-NAME or methylene blue. Activity-directed fractionation of Po.Cr revealed that the gut stimulatory and inhibitory constituents were widely distributed in the aqueous and organic fractions.

This study demonstrates that Ispaghula has a gut-stimulatory effect, mediated partially by muscarinic and 5-HT₄ receptor activation, which may complement the laxative effect of its fiber content, and a gut-inhibitory activity possibly mediated by blockade of Ca²⁺ channels and activation of NO-cyclic guanosine monophosphate pathways. This may explain its medicinal use in diarrhea. It is, perhaps, also intended by nature to offset an excessive stimulant effect.