G. Nijs

Influence of rhein anthrone and rhein on small intestine transit rate in rats: evidence of prostaglandin mediation

The present study was undertaken to investigate the role of prostaglandins in the shortening of transit time observed after intraduodenal administration of rhein anthrone and rhein. After intraduodenal administration of rhein anthrone (0.5-10 mg/rat), a dose-dependent acceleration of small intestinal transit was observed. The effect for rhein (1-10 mg/rat) was far less pronounced. In the same test conditions, analysis of small intestinal tissue revealed a significant increase of prostaglandin E2 (PGE2), reaching its maximum value 30 min after administration of rhein anthrone. The increase in PGE2 found 30 min after administration of rhein was not significant. The effects provoked by rhein anthrone could be largely prevented by pretreatment of the animals with indomethacin (1-3 mg rat) or cortisol (10 mg/rat). It is concluded that prostaglandins play an important role in the acceleration of the transit provoked in rats by rhein anthrone.

The effect of rhein and rhein anthrone on intestinal fluid transport and on large intestine transit in germ-free rats

The effect of rhein and rhein anthrone on the transit and the transport of water and electrolytes in the large intestine was investigated in germ-free rats. After intracaecal administration, neither of the two compounds was found to accelerate the transit of a colour marker through the large intestine. Both drugs reduced the net absorption of sodium and chloride in the colon and enhanced net potassium secretion. Net water absorption was decreased by rhein and even reversed into net secretion by rhein anthrone. Our results show that the secretagogue activity of the compounds is not sufficient to induce laxation in germ-free rats. Furthermore rhein and rhein anthrone had no laxative properties under our experimental conditions.

Influence of rhein anthrone on peristaltic reflex of guinea‐pig isolated ileum: involvement of prostaglandins

1 The influence of rhein anthrone on the peristaltic reflex was studied with a modified Trendelenburg technique in a range from 10−8 m to 4 × 10−5 m, on a normal and reversed guinea‐pig ileum segment. Rhein anthrone had no significant effects on longitudinal muscle tension, intraluminal pressure or volume displacement when tested on the normal segment in doses up to 10−5 m. When applied to the mucosal side (reversed segment), rhein anthrone produced a dose‐dependent increase of longitudinal muscle tension (significant from 10−7 m), of intraluminal pressure (significant from 3 × 10−6 m) and of volume displacement (significant from 10−7 m). The data show that rhein anthrone possesses in vitro activity which is dependent on contact with the mucosa. 2 The action of rhein anthrone on the reversed segment was inhibited by BW755C (a dual inhibitor of cyclo‐oxygenase and lipoxygenase), by indomethacin and by SC19220 (an antagonist of prostaglandin E2 (PGE2) and PGF2α). The effects remaining on longitudinal muscle tension, intraluminal pressure and volume displacement, calculated as percentage (mean ± s.e.mean) of the initial value, were respectively: 13 ± 8; 23 ± 13; 112 ± 5 for BW755C; 66 ± 19; 51 ± 8; 53 ± 8 for indomethacin and 27 ± 12; 13 ± 7; 50 ± 5 for SC19220. It is concluded that arachidonic acid metabolites, especially PGE2 and PGF2α are involved in the effects of rhein anthrone on the reversed segment.

Anthranoids and the Mucosal Immune System of the Colon

The mechanism of action of anthranoids in general and of sennosides at the cellular level is not precisely known. Pseudomelanosis or pseudolipofuscinosis, a condition characterized by the accumulation of pigmented macrophages in the lamina propria, is one of the well-known effects of these products. It is most probably the result of an interaction between apoptotic epithelial cells and the lamina propria cellular infiltrate. Treatment of cell suspensions of intestinal epithelial cells and of human intestinal epithelial cells in culture with rhein anthrone, the active compound of sennosides, demonstrates a direct influence of the drug on these epithelial cells. Low doses induce alterations in cellular shape and organelles consistent with increased metabolism. High doses induce apoptotic changes. The interaction between the epithelial cells and cells of the monocyte/macrophage lineages induces also the release of prostaglandins of the E series as shown by experiments on cell cultures of epithelial cells and peripheral blood cells. An increase of PGE2 release to about 140% of the control value is noted following administration of low doses of rhein anthrone to a combination of human intestinal epithelial cells and human peripheral blood mononuclear cells. This finding indicates that rhein anthrone is activating cellular components of the intestinal immune system and may by this pathway induce secretion and motility.

Conventionalization of germ-free rats reverses the disability of rhein anthrone to induce laxation

This study shows that rhein anthrone has no laxative potency in germ-free rats because after intracaecal administration of a dose of 50 mg/kg the large intestine transit exceeded 240 min. The time course of the laxative potency of rhein anthrone injected intracaecally was evaluated after peroral inoculation of germ-free rats with the caecal contents of conventional rats. Large intestine transit was measured at consecutive periods, on days 0, 1, 2, 3 and 5 after peroral inoculation. It appeared that 1 day after peroral inoculation the laxative potency of rhein anthrone was already established (large intestinal transit < 10 min) and laxation remained on the following days (days 2, 3 and 5). We concluded that rhein anthrone is inactive in germ-free rats and acquires laxative potency after peroral inoculation of germ-free rats with caecal contents of conventional rats.

A rapid method for the estimation of prostaglandin E2 in intestinal tissues using fluorescence derivatization

A sensitive spectrofluorimetric method is described to determine small quantities of prostaglandin E2 in complex biological systems as intestinal tissues. The method is based on a solid phase extraction combined with a coupling with a fluorescent marker and measuring the derivatization product by fluorescence densitometry. After mixing the tissue with an ice-cold perchloric acid solution, adjusting the pH, centrifugation and filtration steps, the prostaglandins are retained on a solid phase extraction C18 disposable column. They are eluted with diethylether, derivatized with 4-bromomethyl-7-methoxy-coumarin using potassium carbonate as condensating agent and finally analysed using fluorescence densitometry on silica gel TLC plates. Applying this method, amounts down to 5 ng (per gram wet tissue) could be measured in intestinal tissues, the s.e.m. for replicated total analysis being less than 15%. The foregoing method is applied for the determination of PGE2 released in the intestinal wall under the influence of laxatives.

Determination of rhein anthrone in caecal content of rats using reversed phase HPLC

Abstract A sensitive spectrofluorimetric method is described to determine small quantities of rhein anthrone in complex biological systems as caecum content and faeces. The method is based on the stability and fluorescent properties of anthrone molecules in borax solution and combines the sensitivity of spectrofluorimetric methods with the resolution power of liquid chromatography. After extraction of the faeces with a solution of sodium tetraborate and ascorbic acid in water and centrifugation, an aliquot of the supernatant is injected on a Sephadex-G25 precolumn. After rejection of the first fractions (fluorophors present in caecal content), rhein anthrone is collected on an RP-C18 column and eluted with an acetonitrile-borax buffer gradient. The anthrone is quantified using a fluorescence HPLC monitor.

In vitro Demonstration of a Positive Effect of Rhein Anthrone on Peristaltic Reflex of Guinea Pig Ileum

The influence of rhein anthrone on the peristaltic reflex was studied with a modified Trendelenburg technique in the range from 10(-8) to 4 x 10(-5) mol/l, using a normal and reversed guinea pig ileum segment. Rhein anthrone had no significant effects on longitudinal muscle tension, intraluminal pressure or volume displacement when tested on the normal segment in doses up to 10(-5) mol/l. When applied to the mucosal side (reversed segment), rhein anthrone produced a dose-dependent increase of longitudinal muscle tension, of intraluminal pressure and of volume displacement. The data show that rhein anthrone possesses in vitro activity which is dependent on contact with the mucosa. The action of rhein anthrone on the reversed segment was inhibited by BW755C (a dual inhibitor of cyclo-oxygenase and lipoxygenase), by indomethacin and by SC19220 (an antagonist of PGE2 and PGF2 alpha). It is concluded that arachidonic acid metabolites, especially PGE2 and PGF2 alpha are involved in the effects of rhein anthrone on the reversed segment.