Protein Catabolism and Urea Utilization in Water-Deprived and Fasted Ground Squirrels and Rats
The objective of this study was to examine a specific metabolic adaptation, namely, the extent to which protein catabolism was changed in long-term water-deprived and starved Spennophilus lateralis, S. spilosoma, and laboratory rats. It was thought from previous studies that the relative amount of protein and fat catabolism affects water balance and thus determines how long an animal will survive water deprivation. Hibernators may possess unique metabolic flexibility in adapting to water deprivation as they apparently adapt to dehydration when they are hibernating.
In the first series of experiments animals· were water deprived for 6 days at 2 seasons and urine volume, urine urea, urine nitrogen and blood urea were determined daily. Urine urea or nitrogen served as the criterion for protein catabolism. In the second experimental series the metabolism of intraperitoneally injected urea was studied to determine the extent of urea nitrogen utilization for nonessential amino acid synthesis. Urine urea and blood urea concentrations were determined 6, 12, and 24 hr postinjection.
Late winter and spring water-deprived ground squirrels excreted more urea than late summer and winter animals. Late winter and spring animals were less tolerant (lost weight at a faster rate) of water deprivation. Less tolerance may be accounted for by a faster rate of muscle catabolism relative to adipose tissue catabolism because muscle tissue catabolism provides fewer calories per gram of tissue than catabolism of adipose tissue. In the urea injection experiment only 50% of the injected urea was recovered in the urine by the time blood urea levels returned to control values. Laboratory rats could utilize urea at only half the rate of ground squirrels and rats were also about as tolerant of water deprivation as the least tolerant squirrels of late winter and spring. Urea injection data was interpreted to indicate that renal retention of urea was occurring and urea nitrogen was being utilized in hepatic synthesis of nonessential amino acids. Thus urea nitrogen utilization may have contributed to the decreased rate and amount of protein catabolism and prolonged life in the long-term water-deprived animals.
It was concluded that there are seasonal and species differences in tolerance to long-term water deprivation and the attendant starvation. The difference in tolerance may be due to the ability to conserve protein-containing tissue. The ground squirrels exhibited seasonal metabolic flexibility by their changing level of adaptation to water deprivation and starvation.
Level of Degree
UNM Biology Department
First Committee Member (Chair)
Marvis L. Riedesel
Second Committee Member
Clifford S. Crawford
Third Committee Member
Fourth Committee Member
Rigler, Gerald L.. "Protein Catabolism and Urea Utilization in Water-Deprived and Fasted Ground Squirrels and Rats." (1972). https://digitalrepository.unm.edu/biol_etds/319