Daily patterns of feeding and excretion in rats confined to metabolism cages: strain and age differences.

Abstract

Data are presented on the daily feeding and excretion patterns of Wistar, Sprague-Dawley and Wistar/Sprague-Dawley hybrid rats confined to metabolism cages. All strains were characterized by the formation of a grossly hypertonic urine which contained high concentrations of both sodium and potassium. Daily concentration rhythms were found in urinary sodium, potassium, calcium and magnesium, but the magnitude of these rhythms depended on strain and age. Rats of all ages were characterized by a high turnover of water and salts. A large proportion of the water was lost by routes other than urine and faeces, and the animals appeared to absorb a slightly hypertonic salt solution from the intestine (the result of eating and drinking) in order to counteract this water loss.