Time course of adaptation to low and high NaCl diets in the domestic fowl. Effects on electrical behaviour of isolated epithelia from the lower intestine.

Short circuit currents (Isc), resting electrical potential differences (p.d.) and resistances were measured in vitro for stripped rectal ("colonic") and coprodeal epithelia from fowls transferred to low from high NaCl diet for 1, 2, 4 or 8 days (NaCl depletion), and from birds adapted to low NaCl diet and sacrificed 8, 16 and 24 h after NaCl-loading (resalination). NaCl-depletion enhanced Isc and p.d. fully by 4 days in rectum but took 8 days in coprodeum (half times 1.2 days and 4 days respectively); rectal amino acid-sensitive Isc was abolished and amiloride-sensitive Isc was established by 4 days (half-time 1 day). Resistance changes were transient and relatively small in rectum, but coprodeal resistance decreased. Resalination reversed these changes very rapidly in both tissues (within 25-50 h; half times 10-20 h). It is concluded that responses to NaCl-depletion are mediated by aldosterone (and possibly by some other unknown agonist); responses to resalination may be due in part to suppressed aldosterone secretion and possibly to the evocation of some other controller (perhaps prolactin or corticosterone) antagonising aldosterone.