Mucin discharge from the isolated vascularity perfused rat colon in response to bile salts

Abstract

The intestinal mucus layer plays an important role in the protection of the mucosa. This function is performed mainly by mucins, which are high molecular-weight glycoproteins produced by goblet cells. Luminal factors that govern mucin secretion are poorly known. The hypothesis that bile salts could induce colonic mucin discharge was thus tested in a model of isolated vascularly perfused rat colon. Methods : Ligated loops (I O-cm length) of rat colon were separated from adjacent tissue, transferred to a saline bath and perfused through the superior mesenteric artery with a Krebs Henseleit buffer containing 25% washed bovine erythrocytes, 3% bovine albumin, amino acids and glucose. After a lO-min control period, loops were filled with Iml of prewarmed saline containing stimulants. After 30-min period of stimulation, mucus was assayed in luminal content by enzyme-linked immunosorbent assay. Tissue samples from perfused rat colon were also immersed in Karnovsky's fixative for subsequent staining of mucus cells with alcian blue followed by the periodic acid schiff reagent. Results : Luminal administration of deoxycholate (I-lOmM) produced a dose-dependent release of mucins (maximal response at 550 % of control loops) in the isolated perfused rat colon. Hyodeoxycholate (IOmM) and Chenodeoxycholate (I0mM) also induced an increase in mucin discharge (response at 310 % and 290 % of controls,respectively) whereas IOmM cholate, ursodeoxycholate and tween-20 were without effect. Taurine conjugated bile salts (deoxycholate,hyodeoxycholate, and chenodeoxycholate) were less potent mucus secretagogues than unconjugated forms. Tetrodotoxin, atropine, indomethacin, a mast cells stabilizer (ketotifen), H I histamine antagonist(pyrilamine) and 5-HT receptors antagonists (ketanserin, SDZ, Zophren) did not significantly modify deoxycholate-induced mucin secretion. Conclusions : The present study conducted with the isolated vascularly perfused rat colon suggests that some bile salts may playa role in the regulation of colonic mucin secretion by way of a direct action on mucus cells