Ultrasonography evaluation of abdominal fat in live rats

We have developed a new noninvasive method of estimating abdominal fat volume in live rats using ultrasonography. By this method, cross sections of perirenal (retroperitoneal) fat tissue, which is an abdominal fat, at the renal vein level could be identified and the area determined. The perirenal fat in Wistar rats (wide body weight range, 111.4 to 497.3 g; limited range, 300.1 to 337.9 g) measured by ultrasonography was compared with the actual fat tissue weight. The cross-sectional area of perirenal fat tissue was significantly correlated to the actual whole tissue weight. Using this procedure, we examined the changes of perirenal fat stores during fasting. Consequently, the cross-sectional area of perirenal fat and its actual weight decreased in parallel. Total body electrical conductivity (TOBEC) is currently used to measure fat-free mass (FFM) and indirectly predicts total body fat mass of live laboratory animals. The body fat distribution, that is, the location of adipose tissue in the abdominal region, is closely associated with obesity-related diseases. Therefore, it is important to focus not only on the accumulation of total body fat, but also on that of abdominal fat. The present ultrasonographic method is considered to be useful for repeated noninvasive measurement of abdominal fat in the live rat.