Sennoside-induced secretion is not caused by changes in mucosal permeability or Na+,K(+)-ATPase activity

Area of Science:

• Gastroenterology
• Pharmacology
• Cell Biology

Background:

• Sennosides are widely used laxatives.
• Their precise mechanism of action on colon physiology is not fully elucidated.
• Understanding the cellular and molecular basis of laxative effects is crucial for therapeutic optimization.

Purpose of the Study:

• To investigate the effects of sennosides and rhein on water and electrolyte transport in the rat colon.
• To determine the role of paracellular permeability and epithelial integrity in sennoside-induced secretion.
• To explore the involvement of Na+,K+-ATPase activity in the laxative mechanism.

Main Methods:

• In-situ rat colon perfusion studies following oral sennoside administration.
• Intraluminal administration of rhein to assess its direct effects.
• Measurement of net water and electrolyte (Na+) transport.
• Assessment of paracellular permeability using erythritol and PEG 1000.
• Analysis of Na+,K+-ATPase activity and epithelial damage markers (LDH release).

Main Results:

• Sennosides and rhein significantly reduced net water and Na+ absorption, inducing secretion.
• Paracellular permeability to small molecules (erythritol) increased 2-3 fold, while large molecules (PEG 1000) were unaffected.
• No significant changes were observed in Na+,K+-ATPase activity or signs of epithelial cell damage.

Conclusions:

• The secretory effect of sennosides and rhein is mediated by increased paracellular permeability to small solutes.
• This mechanism facilitates chloride secretion, osmotically driving Na+ and water.
• Epithelial damage and Na+,K+-ATPase inhibition are not involved in the laxative action of sennosides.