Body-weight regulatory mechanisms and food hoarding in hereditarily obese (fa/fa) and lean (Fa/Fa) zucker rats

Pre- and postprandial rectal temperatures and the defended level of body weight, as inferred from the critical body weight for the onset of hoarding behaviour, were compared in obese (fa/fa) and lean (Fa/Fa) Zucker rats. Body temperatures of the obese group were not significantly lower than those of the lean group, whether satiated or whether subjected to short- or long-term food deprivation. Defended body weights as inferred from the critical weights for hoarding, and the actual weights of the obese (fa/fa) rats were both abnormally high, nearly double those of their lean controls, but the percentage weight losses necessary to elicit hoarding activity were similar in the two groups. Thus the mechanism underlying the obesity of the Zucker rat appears to differ both from that of the hereditarily obese (ob/ob) mouse (which shows defective thermogenesis and is hypothermic) and from the obesity of rats with hypothalamic ventromedial lesions (in which the defended body weight is no higher than in intact controls). Unlike the ob/ob mouse and the ventromedial rat, the obese Zucker rat appears to regulate body weight in a normal way but at an abnormally high level.