ALDOSTERONE AND THE CONTROL OF LOWER INTESTINAL NA- SECRETION IN CHICKENS( ABSORPTION AND CL)

There are several ion-transport systems expressed in the lower intesti nal segments of chickens, depending on the level of the salt intake. T he aim of this study was to test the hypothesis that aldosterone is th e sole regulator of all these ion-transport systems, as had been indic ated by our previous results. Chickens were long-term adapted to low s alt intake, and then switched to a high-salt diet. During the first 5 days of resalination, the birds were injected with aldosterone every 8 hr and then the magnitude and characteristics of the epithelial ion t ransport systems in colon and coprodeum were investigated. The results support strongly the hypothesis that aldosterone exerts major control of the amiloride-inhibitable Na+-transport system in both colon and c oprodeum, as its magnitude was maintained high in spite of the resalin ation process. Spironolactone counteracted the actions of aldosterone, although not totally. On the other hand, aldosterone is not the sole regulator of the hexose/aminoacid-Na+ cotransport systems in colon, al though it can act as their modulator, as the injections did delay the normal increase always seen in these transport systems during resalina tion. Aldosterone can also modulate the Cl--secretory capacity of colo n and coprodeum, but only temporarily. (C) 1997 Elsevier Science Inc.