Ion and Luminal Marker Concentrations in the Gut of Saline-Acclimated Ducks

Abstract

Concentrations of Na+, K+, and C1in digestive tract fluid were measured in eight saline-acclimated domestic Pekin ducks, Anas platyrhynchos, and the concentration of nonabsorbable luminal marker 14C-polyethylene glycol ('4C-PEG, orally loaded in 180 mM NaC1) was measured in five of these birds. The birds were sacrificed and the gut was ligated into sections. All sections were hyponatremic to plasma; [C1-] in the proventriculus and ventriculus were equal to and higher than plasma [C1-], respectively, and elsewhere [C1-] was less than plasma [C1-]. The [Na+]/[K+] ratio (1.5 or less) was lower than that of birds without salt glands (2-3, Hurwitz et al. 1970). The initial 10-fold dilution of ['4CPEG] in the duodenum and subsequent 80-fold increase in ['4C-PEG] in the ileum are consistent with secretion into the duodenum and net absorption of Na+ and water in the ileum. Rectal (and cecal) ['4C-PEG] was 5-fold lower than ileal ['4C-PEG], a decrease presumably due to retropulsion of urine into the rectal-cecal complex. These observations suggest sodium-replete ducks continue to reflux urine into the hindgut where NaC1 and water uptake have been shown to occur (Skadhauge et al. 1984) and offer indirect evidence that hindgut NaCl reabsorption and extrarenal NaCl secretion may be linked.