The effect of age on the control of water conservation in the laboratory mouse--metabolic studies

Age-related changes in the intake of food and water, and the output of faeces and urine were investigated in C57BL/Icrfat mice of 6 and 24 months of age. Animals were singly housed in a metabolic cage for a period of 30 days. 14 days were allowed for acclimatization before the animals were dehydrated for 24 hours. 10 days of rehydration were allowed prior to a hyperosmotic challenge with 3% sodium chloride in the drinking water. The animals were then observed for 5 more days of rehydration. Urine was collected and analysed with regard to sodium, potassium, urea and vasopressin output/24 hours (/100g body weight), and the osmotic pressure of the urine was determined. Data were analysed by a 2 factor analysis of variance with repeated measures on one factor. Significant changes were detected in the control of body weight, potassium, sodium and urea outputs. No age-differences were detected in the intake of food or water, the output of faeces or urine, the urine osmotic pressure or the excretion of vasopressin. However, significant changes in these variables were detected in both age groups on the days of physiological challenge. The conclusion drawn is that in the mouse strain studied, and for the period of the lifespan investigated, there is no age related defect in the secretion of vasopressin. However, there are trends in the data suggesting a decreased responsiveness of the kidney with age.