EVER HIGHER - CONSTANT RISE OF BODY-WEIGHT SET-POINT IN GROWING ZUCKER RATS

The mass of food hoarded by rats given access to food only 2 h per day is proportional to the rats' body weight deficit. The intersect of th e regression line of hoarded food plotted against body weight gives an indication of the body weight set-point. In the present work, the hoa rding behavior of six obese and six control rats was measured every da y at various body weights from 8 to 24 weeks of age. Every other week the animals were anesthetized and their percentage of fat was measured in vivo with a total body electrical conductivity method (TOBEC). Lea n mass and body length of the obese, and their controls, increased sim ilarly in both groups over the period of the measurements. On the othe r hand, the body weights increased more in obese, from 174 +/- 5 to 72 9 +/- 18 g (n = 6), than in controls, from 157 +/- 5 g to 452 +/- 14 g (n = 6). The body weight set-point, calculated every other week for b oth groups of rats, increased progressively with age. At the age of 24 weeks, the mean set-point for body weight regulation was 758 +/- 13 g in obese and 467 +/- 12 g in controls. This result suggests that the obese fa/fa rat defends its fat content, or a variable correlated to t he fat content.