Aldosterone and the control of lower intestinal Na⁺ absorption and Cl^- secretion in chickens

There are several ion-transport systems expressed in the lower intestinal segments of chickens, depending on the level of the salt intake. The aim of this study was to test the hypothesis that aldosterone is the sole regulator of all these ion-transport systems, as had been indicated by our previous results. Chickens were long-term adapted to low salt 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-transport systems in colon and coptodeum were investigated. The results support strongly the hypothesis that aldosterone exerts major control of the amiloride-inhibitable Na⁺-transport system in both colon and coprodeum, as its magnitude was maintained high in spite of the resalination 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, although it can act as their modulator, as the injections did delay the normal increase always seen in these transport systems during resalination. Aldosterone can also modulate the Cl^- secretory capacity of colon and coprodeum, but only temporarily.