AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 1 183-R188, Copyright © 1984 by American Physiological Society
Reduced energy expenditure after ventromedial hypothalamic lesions in female rats
T. R. Vilberg and R. E. Keesey
Activity, O2 consumption, and body composition were measured in female rats
with lesions of the ventromedial hypothalamus (VMH). One group of lesioned
rats was food restricted to maintain body weights at control levels. O2
consumption of these food-restricted VMH-lesioned rats was 13% lower than
that of nonlesioned rats. About half this energy savings accrued from
reduced activity; the remainder resulted from a decline in resting
metabolic rate (RMR). Though matched in weight to controls, the body
composition of the restricted VMH-lesioned rats was abnormal. Their carcass
protein was reduced by 12%, whereas fat was elevated 200%. The replacement
of lean metabolically active tissue by carcass fat appears to underlie the
reduction in RMR, an interpretation supported by multiple-regression
analysis of carcass composition. Ad libitum-fed VMH-lesioned rats did not
show this carcass protein decline, though their fat was elevated 895%.
These results confirm that reduced activity contributes to energy savings
and weight gain after VMH lesions. Likewise, restricting weight of
VMH-lesioned rats to control levels reduced RMR, apparently because carcass
protein declines. But, since ad libitum-fed female VMH-lesioned rats do not
display reduced carcass protein, the historic assumption that RMR
reductions contribute to their obesity appears unwarranted.
