Renal function during osmotic stress in the aquatic toad Xenopus laevis.

MCBEAN, RALPH L., AND LEON GOLDSTEIN. Renal function during osmotic stress in the aquatic toad Xenopus laevis. Am. J. Physiol. 2 19 (4) : 1115-1123. 1970.~Xenopus toads, which are normally aquatic and arnmonotelic, became ureotelic after maintenance in a hyperosmotic saline solution for 2-3 weeks. In addition, blood urea levels were elevated more than 15-fold, and this increase contributed significantly to achieving osmotic balance in the animals. Within a few hours after transfer of the toads to saline, urine flow fell to ${o of the rate in freshwater. By 7 days after transfer, flow had returned to about one-fourth of the freshwater level, where it remained. Changes in glomerular filtration rate paralleled those in urine flow. It was estimated that the reduction in urine flow was essential to the observed urea accumulation; however, an increase in net urea synthesis also appeared necessary. The suppression of urine flow in Xenopus after transfer to saline appeared to be related to an increase in plasma sodium concentration. Dehydration per se did not occur.