Atrial natriuretic factor inhibits Na-K-Cl cotransport in teleost intestine.

Addition of atrial natriuretic factor (ANF) to the contraluminal side of the intestinal mucosa of a marine teleost, the winter flounder Pseudopleuronectes americanus, inhibits short-circuit current, net transepithelial fluxes of Na and Cl, and the unidirectional influx of Rb across the brush border membrane. This action of ANF is closely mimicked by addition of 8-bromo-guanosine 3',5'-cyclic monophosphate (8-BrcGMP). In contrast to the intestine, the opercular epithelium of the flounder did not respond to the in vitro addition of either ANF or 8-BrcGMP. Because intestinal salt and water absorption diminishes when marine fish enter water of lower salinity, ANF may be an important hormonal regulator through which euryhaline fish adapt to varying salinities.