Effects of cold exposure and dehydration on renal function in black-tailed prairie dogs

Black-tailed prairie dogs (Cynomys ludovicianus) were deprived of food and water for several weeks during the fall and winter in a cold-room hibernaculum (Ta 5–8 degrees C), and for several days at room temperature during the summer. Body temperatures (Tb) were determined periodically in nine animals by radiotransmitters implanted in the abdomen. Animals deprived of food and water in the summer were killed when maximum urine concentration was achieved. Eight animals in the winter were active when killed after 7–35 days in the hibernaculum with Tb between 18 and 36 degrees C. Five animals that became torpid periodically in the winter were killed after 19–42 days in the hibernaculum when their Tb indicated torpor (Tb less than 13 degrees C). Active animals in the summer and winter possessed pronounced renal corticomedullary urea and sodium concentration gradients. Torpid animals lacked these gradients and had lower urine and plasma osmotic concentrations than active animals. Plasma urea values and terminal osmolal U/P ratios were lowest in torpid prairie dogs.