Water Balance and Kidney Function in Four Species of Rattus From Ecologically Diverse Environments.

Abstract

While Rattus fuscipes survived only 4 days of water deprivation at 21ºC, R. norvegicus, R. villosissimus and R. lutreolus survived 13-16 days. There was considerable inter-individual variation in the response of water-deprived R. villosissimus. Analysis of osmotic pressure, urea, sodium, potassium and chloride of both plasma and urine of rats with and without drinking water revealed that: (1) the abilities of R. norvegicus and R. villosissimus to tolerate water deprivation were due in large part to their abilities to produce highly concentrated urine; (2) R. lutreolus tolerated long periods of water deprivation not by urine-concentrating ability but by partly abandoning homeostasis and tolerating elevated levels of plasma solutes; (3) water-deprived R. fuscipes excreted large volumes of concentrated urine, possibly because their relatively high metabolic rate necessitated the excretion of excess metabolites. In all of the rats, urea constituted an unusually low proportion of the total osmotic pressure. The water-balance response of water-deprived rats is at variance with both their macrogeographical distribution and microhabitat preferences.