Cloacal resorption of salt and water in the Galah (Cacatua roseicapilla)

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Abstract
1. The transmural net flow of salt and water in the coprodeum and large intestine of the Galah (Cacatua roseicapilla), an Australian xerophilic parrot, was measured by an in vivo perfusion technique. The main goal of the study was to understand what happens when the hyperosmotic ureteral urine formed in the dehydrated state is regurgitated into the cloaca. Buffered perfusion fluids, hyper- and isosmotic to plasma, with varying NaCl and KCl concentrations, were used. [(14)C]polyethylene glycol served as an unabsorbable water marker.2. The cloacal Na(+) and Cl(-) absorption rates were nearly parallel and at low luminal concentrations roughly proportional to the intraluminal concentrations. At higher concentrations the Na(+) absorption rate showed saturation. The maximal Na(+) flow was 217 muequiv/kg.hr, the concentration at half maximal flow 181 m-equiv/l. The Na(+) absorption rate was not impaired by a high K(+) concentration. K(+) was secreted into the intestine, except at high intraluminal K(+) concentrations where resorption was observed.4. The apparent osmotic permeability coefficient was 0.85 mul./kg.hr.m-osmole at an average osmotic difference of 446 m-osmole between lumen and plasma; it was higher at lower differences. In the (near) absence of an osmotic difference across the cloacal epithelium the solute-linked water flow was 5.0 mul. H(2)O/muequiv Na(+).5. It is concluded that the hyperosmotic ureteral urine formed in the dehydrated state can pass into the cloaca without a water loss. A Na(+) absorption of around 70% of the ureteral output is likely.