Effect of the stable prostacyclin analogue iloprost on water and electrolyte transfer of the rat ileum and colon in vivo.

The effect of iloprost on water and ion transfer was measured simultaneously in tied-off loops of the rat ileum and colon in vivo. (1) In the ileal loops iloprost had no effect on water and ion transfer neither by intraluminal, nor intraaortal or intravenous application. (2) In the colonic loops only intraaortal bolus application of the high dose of 500 micrograms iloprost significantly decreased net water, sodium and chloride absorption, but did not induce net secretion. (3) Inhibition of endogenous prostaglandin synthesis by indomethacin did not change net water and electrolyte transfer in the ileum and colon. (4) Under this pretreatment i.v.-application of 100 micrograms iloprost, ineffective without indomethacin, induced a net secretion of water and sodium and inhibited absorption of chloride in the colon. (5) At the same time iloprost had no effect in the ileal loops of the same animals. (6) Potassium secretion was activated already by 100 micrograms iloprost administered intraluminally. We conclude from this study, that prostacyclin and iloprost have a specific secretory action in the colon. However this effect is masked under in-vivo conditions, either by interactions of ineffective prostaglandin metabolites with the concerned receptors or by counteracting prostaglandins, and becomes evident only after inhibition of the prostaglandin biosynthesis.