Renal responses to chronic cold exposure.

The aim of this study was to assess our hypothesis that the release of antidiuretic hormone (ADH), the renal concentrating response to ADH, or both is decreased by prolonged cold exposure. Six groups (n = 6/group) of rats were used. Three groups were exposed to cold (5 degrees C), whilethe remaining three groups were kept at room temperature (25 degrees C). It was found that urine osmolality decreased significantly and serum osmolality increased significantly during cold exposure. The ratio of water/food intake was not affected by prolonged cold exposure. However, prolonged cold exposure increased the ratio of urine output/food intake in the cold-exposed rats, indicating that more urine flow is required by the cold-exposed rats to excrete the osmotic substance at a given food intake. The difference between water intake and urine output decreased significantly in the cold-exposed rats. Thus, prolonged cold exposure increases water loss from excretion. Renal concentrating responses to 24-h dehydration and Pitressin were decreased significantly in the cold-exposed rats. Plasma ADH levels remained unchanged, but renal ADH receptor (V2 receptor) mRNA was decreased significantly in the cold-exposed rats. The results strongly support the conclusion that cold exposure increases excretive water loss, and this may be due to suppression of renal V2 receptors rather than inhibition of ADH release.