Effects of cortisol on water transport across the eel intestine.

Transepithelial potential difference (PD) and net water flux were estimated simultaneously in the posterior part of the intestine isolated from Japanese eels with special reference to the role of cortisol in the sea-water adaptation of the intestine. When cortisol was previously injected into freshwater eels, the serosa negativity of the PD, water flux and osmotic permeability (Po) increased at 24 hr after the injection and attained the levels of sea-water eels. Cortisol injection into sea-water eels further increased the Po. When cortisol was added to the serosal fluid of the isolated intestine from sea-water eels, the water flux and tissue water content increased after 7 hr. With the intestine from hypophysectomized fresh-water eels, similar treatment with cortisol enhanced the water flux, tissue water content and serosa negativity of the PD, whereas no such in vitro effects of cortisol was observed in intact fresh-water eels. These results indicate that cortisol acts directly on the intestinal epithelium and increases the serosa negativity of the PD and water permeability. Absence of in vitro effect of cortisol in the fresh-water eel seems to be due to antagonistic effect of prolactin.