Quiescent Sex Differences in C57BL/6J Mice

Background: Many studies focus on male animals, with fewer studies explicitly studying female animals. Studies have found sex differences in various kidney disease states, such as acute kidney injury and chronic kidney disease, although sex differences in unaltered animals remain underexplored. Methods: Male and female C57Bl6/J mice were purchased from Jackson labs at 6 weeks of age. Mice had access to standard chow, ad libidum. During the study period, glomerular filtration rate (GFR), plasma creatinine (PCr), and whole blood parameters, including electrolytes, were measured. At 18 weeks of age, mice were euthanized, tissues collected, and complete blood count parameters were measured Results: Neutrophil count and absolute percent were lower in female mice, although absolute percent of lymphocytes were higher. Male mice had higher red blood cell distribution width, and mean platelet volume, compared to female mice. Hemoglobin and hematocrit did not persistently differ between sexes. Slight differences in electrolyte balance were found, with higher sodium and lower potassium in female mice. Chloride levels did not differ. Although pH and PCO2 was not different between sexes, HCO3- levels were higher in male mice, and anion gap was higher in female mice. Direct and indirect measures of renal function, including PCr, GFR, and BUN, did not persistently differ between male and female mice. Conclusion: Our study provides insight into sex differences at baseline in parameters that directly and indirectly affect kidney function. These quiescent differences may reflect in a sex differential in the capacity to respond to renal insults. Funding: NIDDK Support