Orchiectomized Fischer 344 male rat models body composition in hypogonadal state

The hypogonadal state in men is accompanied by substantial decreases in muscle and bone mass and by an increase in adiposity. Most of the strains of orchiectomized (ORX) rat that have been used to model this state display substantial losses in bone, but only subtle changes in adiposity and muscle mass. In order to identify a rat model displaying a robust catabolic response to ORX, we studied three strains: Fischer 344 (F344), Brown Norway and Wistar. ORX caused a significant and sustained decrease in weight gained by F344, but only a trend toward reduced weight gain in Brown Norway rats and a modest reduction weight gain in Wistar rats that was significant only after 56 days. ORX suppressed food intake in F344 rats, and to a lesser degree in Brown Norway and Wistar rats. ORX reduced muscle mass significantly in F344 rats, but not in Brown Norway or Wistar rats. ORX increased adiposity moderately in F344 rats and substantially in Wistar rats. ORX caused a marked reduction in prostate mass and increase in bone resorption in all three strains. Thus, F344 was the only strain in which ORX produced substantial decreases in food intake, body weight and muscle mass with increased adiposity and increased bone resorption. We conclude that the F344 rat displays a broad range of catabolic effects following ORX and is the best rat model for studying the androgenic pathway and strategies for reversing catabolic changes induced by hypogonadism.