Concentration of urine by the hibernating marmot.

Studies wer performed with marmots (Marmota flaviventris) of both sexes that had chronic arterial, venous, and bladder catheters. Urine collection was performed during hibernation and urine osmolalities (611.6 not equal to 166.1 SD) were found to be lower than those of aroused animals (1264 not equal to 472.9 SD), but hypertonic to plasma. Peak osmolality of meduallary slices was found to be in the range of osmotic pressures of urine obtained from hibernating or aroused animals. After single injections of a mixture of rho-aminohippurate and inulin, or during constant infusion of inulin, steady-state excretion by hibernators was not achieved for several days. Indirect evidence indicateds that the hibernating marmot is capable of PAH secretion.