Reevaluation of the sand rat as a model for diabetes mellitus

The North African sand rat, Psammomys obesus, has been claimed to be a valuable model for investigating diabetes. It has been reported that, in the laboratory with free access to food, sand rats overeat, become obese, and develop hyperglycemia and ketoacidosis. We have observed that, although sand rats from our colony become obese and hyperinsulinemic, hyperglycemia is rare and ketoacidosis is virtually nonexistent. Because age, obesity, and dietary sucrose have been reported to be risk factors for diabetes, we have attempted to cause diabetes in a large group of sand rats by inducing obesity through sucrose feeding over an extended period of time. Animals fed sucrose-rich diets were compared to controls fed normal carbohydrate (starch) diets. No group of animals studied over 18 mo developed hyperglycemia and virtually all groups maintained small but significant glucose-induced acute insulin responses. Hyperinsulinemia and insulin resistance accompanied obesity, but there were no differences between dietary groups. Lean sand rats fed sucrose had higher circulating levels of triglyceride (TG) and accelerated TG secretion rates (TGSR) compared to lean controls. After a longer period of observation, all sand rats had elevated plasma TG levels, however, TGSR were normal, indicating that TG removal may have become defective. Although this animal is an excellent model in which to examine spontaneous obesity, Psammomys obesus is a poor model for the study of human diabetes mellitus.