Sex differences in age development of a mouse inbred strain: body composition, adipocyte size and organ weights of liver, heart and muscles.

The mouse inbred strain HLG has only recently been submitted for international registration. It has been widely used in radiological studies. Since these mice tend to become obese, they may be of interest for studies concerning fat metabolism. Therefore, the present ageing study examines the sex-specific development of body weight, body composition, adipocyte size as well as the organ weight of liver, heart and thigh muscles of the inbred strain HLG (54 males/53 virgin females) between day 40 and 360 of life. The body weight development showed a distinct sexual dimorphism, quickly increasing in the case of males but comparatively protracted in females until maturity. Significantly higher values for body and fat-free dry weight as well as body water were found in males of all ages. Body fat and adipocyte diameter were only higher in the 80 and 120 day-old males. Thus, the increase in female body weight resulted largely through a rise in body fat as additionally evidenced by the sex-specific correlation of characteristics. A 2-fold analysis of variance showed sex differences in the relative weights of liver and muscle, but not of the heart. A sex-specific close correlation was observed between body and liver weights in males until day 180. Correlations between body fat and other characteristics were only rarely found. Differences in coefficients of variation largely depended on the characteristics. A higher variability was also found for some characteristics in the youngest groups (40 days). A sex-specific difference was only seen in the case of body fat content for 60 day-old mice (female > male).