Glomerular filtration rate and urine concentration in the dromedary camel in dehydration

The glomerular filtration rate (GFR), effective renal plasma flow (ERPF), urine osmolality, urine flow rate, urea excretion, osmolar clearance, and free water reabsorption were measured in a group of 5 female dromedary camels in control conditions and also after 10 days dehydration in both early and mid-summer. There was a loss of 23% in mean body weight and a fall of 75% in GFR in severe dehydration, with a parallel reduction in ERPF and in urine flow rate. Urine osmolality reached a mean maximum of 1,466 mosm/kg in severe dehydration of mid-summer, the highest individual urine osmolality being 2,372 mosm/kg. Osmolar clearance, free water absorption and urinary urea excretion were lower in dehydration. Urea/inulin clearance ratio was significantly lower in dehydration (p <0.001). Sodium excretion did not change in dehydration. Fractional reabsorption of urea was higher in dehydration, reaching a maximum value of 74% of the filtered load. The fall in urinary urea concentration was one of the factors contributing to the poor concentrating ability of the severely dehydrated camel kidney, probably caused by the fall in GFR and increase in tubular re-absorption of urea, rather than by protein deprivation.