Influence of serosal hydrostatic pressure on net water and electrolyte transport across the isolated rat colonic mucosa exposed to different secretagogues.

The influence of 2 cm and 7 cm hydrostatic pressure applied upon the serosal side on net water and electrolyte transport and paracellular permeability was investigated in everted sacs of stripped rat colon mucosa exposed to different secretagogues. A 2 cm pressure abolished net fluid absorption in the presence of deoxycholic acid, bisacodyl, ethacrynic acid and rhein and reduced absorption in the tissue pretreated with cholera toxin. The paracellular permeability was increased by deoxycholic acid, bisacodyl and ethacrynic acid and diminished under the influence of rhein and cholera toxin. At a pressure of 7 cm H2O fluid movement was directed toward the mucosal side parallel to the increase of the paracellular permeability. The fluid appearing at the mucosal side was isotonic in the presence of deoxycholic acid, ethacrynic acid and rhein but hypotonic when the tissue was pretreated with cholera toxin. From the pressure-induced net water flow and the composition of the transferred fluid secretagogues acting predominantly on paracellular pathway can be distinguished from secretagogues acting on basis of other mechanisms.