KIDNEY STRUCTURE AND FUNCTION OF OBLIGATE AND FACULTATIVE HIBERNATORS- THE WHITE-TAILED PRAIRIE DOG (CYNOMYS LEUCURUS) AND THE BLACK-TAILED PRAIRIE DOG (CYNOMYS-LUDOVICIANUS)

The white-tailed prairie dog is an obligate hibernator that enters a h eterothermic phase when maintained in the cold with low intensity ligh t and ad libitum food and water. The black-tailed prairie dog (a facul tative hibernator) will not hibernate under similar conditions. It has been suggested that the black tailed prairie dog remains active durin g the winter because it can conserve water more effectively due to a m ore efficient kidney. The present study revealed no significant differ ences between the species in renal morphology: relative medullary thic kness, nephron heterogeneity, renal vasculature, or fornix dimensions, all of which are structures associated with the urinary concentrating mechanism. In addition, there was no difference in number of nephrons between the two species. The black-tailed prairie dog does produce a more concentrated urine when food and water deprived. However, this di fference was not observed when the animals were salt loaded. The water -deprivation and salt-loading experiments suggest that the higher urin e osmolality produced by the back-tailed prairie dog during fasting is a result of a higher urea load due to a greater protein catabolism an d not because of a differential capacity to concentrate urine.