Medullary Sodium and Urea Gradient of the Dog Kidney in Hypothermia

SummaryThe kidneys were removed from 11 euthermic and 8 hypothermic (average rectal temp. 25°C) dogs and four slices of the tissue from papilla to cortex were taken from each kidney. The Na, K, and urea concentrations of the slice were then determined in slice extracts. Although urine osmolality was significantly reduced in hypothermia, the papillary Na and urea concentrations at a given urine osmolality were markedly higher in hypothermic kidneys than in euthermic, suggesting that the impairment of renal concentrating ability in hypothermia is partly attributable to a failure of the collecting duct urine to osmotically equilibrate with the surrounding media. On the basis of the latter finding, it is postulated that the action of ADH is less effective in hypothermia.