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Introduction: Current animal-based biomedical research, including studies on liver function and disease, is conducted almost exclusively on male animals to mitigate confounding effects of the estrous cycle. However, liver diseases afflict both men and women, so translational research findings should also be applicable to female patients. This pilot study investigated sex differences in objective and subjective severity assessment parameters in rats following 50% partial hepatectomy. Materials and Methods: This study was performed using Wistar-Han rats, in which measurements of body weight, spontaneous motor activity in the Open Field (movement distance, movement velocity, rearing frequency), and fecal corticosterone metabolites (FCMs) were conducted at baseline and at multiple times after partial hepatectomy. Subjective post-surgical severity assessments were conducted using modified score sheets. Blood parameters such as leukocyte count and serum aspartate aminotransferase (AST), as well as estrogens and testosterone were measured from samples obtained during partial hepatectomy and at sacrifice. In addition, the amount of resected liver tissue was measured at partial hepatectomy and the proliferated liver was weighed at sacrifice. Results: Fecal corticosterone metabolite concentrations differed significantly between males and females at baseline and following hepatectomy. Also, leukocyte counts and estrogen concentrations were significantly different between sexes before partial hepatectomy. Alternatively, there were no sex differences in severity assessments, body weight changes, and behavior in the Open Field (OF) at any measurement time point. Liver weight was significantly different in males and females at the time point of partial hepatectomy and sacrifice. Discussion/Conclusion: The results of this pilot study suggest that males and females respond similarly following partial hepatectomy. Examination of both sexes is very important for translation to humans, where both men and women suffer from liver disease. Furthermore, the use of both sexes in animal-based research would improve the utilization of the animal breeding in terms of the 3Rs. However, due to some limitations, larger scale investigations including a broader spectrum of pathophysiolological, behavioral, and pharmacokinetic measures are planned.

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