Submitted on April 29, 2007
Accepted on July 9, 2007
A comparative study of renal function in the desert adapted spiny mouse and the laboratory adapted C57BL/6 mouse; Response to dietary salt load
Hayley Dickinson1*, Karen M Moritz2, E. Marelyn Wintour3, David W. Walker4, and Michelle M. Kett5
1 Monash Immunology and Stem Cell Laboratories, Monash University, Clayton, Victoria, Australia; Physiology, Monash University, Melbourne, Victoria, Australia
2 Anatomy and Cell Biology, Monash University, Clayton, Victoria, Australia
3 Physiology, Monash University, Clayton, Victoria, Australia
4 Physiology, Monash University, Melbourne, Victoria, Australia
5 Physiology, Monash University, Building 13F, Clayton, Victoria, 3793, Australia
* To whom correspondence should be addressed. E-mail: hayley.dickinson{at}med.monash.edu.au.
The desert adapted spiny mouse has a significantly lower glomerular number, increased glomerular size, and a more densely packed renal papillae compared to the similarly sized, laboratory adapted C57BL/6 mouse. In the present study we examined the functional consequences of these structural differences in young adult male spiny and C57BL/6 mice and detailed the impact of one week of a high salt (10% NaCl w/w) diet. Basal food and water intake, urine and faeces production, and urinary electrolyte concentrations were not different between species, although urinary urea concentrations were higher in spiny mice (P<0.05). On normal salt, MAP of the anaesthetised spiny mouse was approximately 18 mmHg lower, ERPF 40% lower (P<0.001), and GFR tended to be lower than the C57BL/6 mouse. On the high salt diet, both species had similar 24h NaCl excretions; but C57BL/6 mice required a significantly increased amount of water (lower urine concentration) than the spiny mice. Filtration fraction was greater in both species on the high salt diet. Spiny mice had greater GFR and ERPF after the high salt diet, whereas the C57BL/6 mouse showed little change in GFR. The ability of the spiny mouse to tolerate a significantly higher plasma osmolality after salt, measured by a decreased drinking response, and the ability to increase ERPF at a lower MAP, are features which allow this species to conserve water more efficiently than can be done in the C57BL/6 mouse. These are important particularly as the desert mouse has a smaller kidney, with fewer nephrons.
