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Aim of the study: Lubricating gut pill (LGP), a traditional Chinese formula, was widely used for the treatment of chronic constipation, especially in the elderly, in China. However, it is unclear whether LGP-induced laxative and/or lubricating effect is involved in water and electrolytes transport in distal colonic epithelium. Materials and methods: The present study was designed to evaluate the effect of LGP on Cl− secretion across rat distal colonic epithelium mounted in Ussing chambers, and on a rat constipation model induced by loperamide, respectively. Results: Application of LGP in the apical side elicited a sustained increase in short circuit current (I SC) response in a concentration-dependent manner. Evidence that LGP-stimulated I SC was due to Cl− secretion is based on inhibition of current by (a) a Na+–K+–2Cl− cotransporter inhibitor bumetanide, (b) removal of Cl− ions in bath solution, and (c) the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel blocker DPC, suggesting that a apical cAMP-dependent Cl− channel was activated. LGP-stimulated I SC was also strongly inhibited by pretreatment with clotrimazole, indicating that the basolateral K+ channel was also involved in maintaining this cAMP-dependent Cl− secretion. Pretreatment of tissues with indomethacin, but not atropine, tetrodotoxin or hexamethonium, inhibited LGP-induced response. In a rat constipation model, oral administration with LGP was significantly restored number of fecal pellets, water content and mucus secretion compared with loperamide-treated group alone. Conclusions: LGP enhances Cl− secretion that is mostly mediated through the release of cyclooxygenase metabolites, by which provided an osmotic force for the subsequent laxative action observed in the rat constipation model. [Copyright &y& Elsevier]

Abstract: Aim of the study: Lubricating gut pill (LGP), a traditional Chinese formula, had been conformed to improve the loperamide-induced rat constipation by stimulation of Cl− secretion, but its mechanism has not been fully explored. Thus, the purpose of this study was to identify the action sites of LGP-stimulated Cl− secretion across rat distal colonic mucosa. Materials and methods: Rat distal colonic mucosa was mounted in Ussing chambers and short circuit current (I SC), apical Cl− current and basolateral K+ current were recorded. Intracellular cyclic adenosine monophosphate (cAMP) content and protein kinase A (PKA) activity were determined with ELISA kit and the non-radioactive PepTag test, respectively. Results: LGP at 800μg/ml elicited a sustained increase in Cl− secretory response, which was inhibited by CFTRinh172, a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor. Permeabilizing apical membrane with nystatin revealed that LGP-stimulated basolateral K+ current was significantly inhibited by KCNQ1 K+ channel inhibitor chromanol 293B. LGP-stimulated I SC was markedly reduced by pretreatment with cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2amine (MDL-12,330A) and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not with inhibitors of Ca2+-dependent signaling pathway. Treatment of tissue with LGP resulted in an increase in intracellular cAMP level and the activation in protein kinase A. The E-prostanoid4 (EP)4 receptor antagonist L-161,982 completely eliminated LGP-induced response. Conclusions: The results showed that LGP enhances Cl− and fluid secretion via prostanoid receptor signaling and also cAMP and protein kinase A pathway, subsequently triggering the activation of apical Cl− channels mostly CFTR and basolateral cAMP-dependent K+ channel. [ABSTRACT FROM AUTHOR]