NATRIURETIC PEPTIDE INHIBITION OF INTESTINAL SALT ABSORPTION IN THE JAPANESE EEL - PHYSIOLOGICAL SIGNIFICANCE

Electrophysiological studies in vitro demonstrated the significant inh ibition by natriuretic peptides (NP) of short-circuit current across t he eel intestine, an important osmoregulatory organ. Inhibitory potenc ies of several members of the NP family were assessed by voltage-clamp determination of net transepithelial salt absorption measured as the short-circuit current I-sc across the intestine of the freshwater-adap ted (FW) and seawater-adapted (SW) Japanese eel (Anguilla japonica); t he order of potency of synthetic eel peptides was: amidated atrial nat riuretic peptide (ANP-NH2) > ventricular natriuretic peptide (VNP) > a trial natriuretic peptide (ANP) much greater than C-type natriuretic p eptide (CNP). Neither the order of potency nor the absolute potencies were effected by salinity adaptation. The observed potency sequence su ggests that inhibition of intestinal absorption is mediated by A-type guanylyl cyclase-coupled NP receptors. The relatively low sensitivity of the intestinal response to NP compared with circulating NP concentr ations suggests a role for intestinal regulation by NP which is indepe ndent of systemic delivery from cardiac sources. A novel model, incorp orating the known immunohistochemical localization of NP-ergic cells a nd processes in the epithelial layer of the intestine and the dissipat ion of the Na+ electrochemical gradient along the alimentary tract, is developed in which local secretion of NP (in response to a bolus of f ood) inhibits salt absorption across the intestine regionally in favor of increased nutrient absorption.