Renal compensation for cecal loss in Gambel's quail (Callipepla gambelii)

Some studies have implicated the avian digestive cecae as important sites of water and solute reclamation working in concert with the lower intestine and the kidneys as part of an integrated osmoregulatory system. In Gambel's quail (Callipepla gambelii), we studied compensatory adjustments in renal function on days 6–7 and 16–17 following ligation of cecae. Plasma osmolality (P_osm) varied significantly between groups with sham-operatd birds (Cs), with an average (P_osm) of 348 mOsm/kg H₂O and quail with ligated cecae (Cx) having a (P_osm) of 355 mOsm/kg H₂O. We detected no change in the rate of glomerular filtration (GFR) between experimental and control groups either shortly after cecectomy or after 16–17 d following surgery. Regression analysis of GFR and urine flow rate (V) showed that Cx birds had a significantly lower V at a given GFR than did controls, evidence that Cx quail absorbed more fluid in their renal tubules. Increased fluid reabsorption was apparently driven by an enhanced reabsorption of sodium. Indeed, sodium excretion was lower in Cx quail as compared to sham-operated birds. On days 6–7, Cx quail drank more water than Cs birds, but by days 16–17 drinking rates were similar. At the end of the experiments, Cx quail showed a proliferation of microvilli along the apical membrane of the rectum, an adjustment consistent with the idea that the rectum alters its absorption capacity to adjust for the loss of cecal function.