AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 1 33-R38, Copyright © 1992 by American Physiological Society
Relationship of adipocyte size to hyperphagia in developing male obese Zucker rats
J. R. Vasselli, J. A. Fiene and C. A. Maggio
Miles Institute for Preclinical Pharmacology, West Haven, Connecticut 06516.
In growing male obese Zucker rats, hyperphagia reaches a maximum or
"breakpoint" and declines at an earlier age with high fat than with
chow-type diets. A serial adipose tissue biopsy technique was used to
correlate changes of retroperitoneal adipocyte size and feeding behavior in
5- to 7-wk-old male lean and obese rats fed laboratory chow or a 35% fat
diet until 30 wk of age. Although chow-fed groups had significantly greater
cumulative intake, fat-fed groups had significantly greater body weight
gain, retroperitoneal depot weight, and adipocyte number. Mean adipocyte
size increased continuously in chow-fed groups but decreased over weeks
20-30 in fat-fed groups, reflecting increased adipocyte number. In fat-fed
obese rats, hyperphagia reached a breakpoint at 11 wk and disappeared by 13
wk. In chow-fed obese rats, hyperphagia reached a breakpoint at 15-16 wk
and disappeared by 19 wk. Biopsy samples revealed that adipocyte size of
fat-fed obese rats was already close to maximal at 10 wk (1.12 micrograms
lipid), while that of chow-fed obese rats only approached maximal at 20 wk
(0.81 microgram lipid). At these time points, lipoprotein lipase activity
paralleled adipocyte size. These data indicate that the duration of the
growing obese rat's hyperphagia coincides with adipocyte filling and
suggest the existence of feeding stimulatory and inhibitory signals from
adipose tissue.
