AJP - Regulatory, Integrative and Comparative Physiology, Vol 248, Issue 1 120-R124, Copyright © 1985 by American Physiological Society
Insulin increases body fat despite control of food intake and physical activity
N. Torbay, E. F. Bracco, A. Geliebter, I. M. Stewart and S. A. Hashim
The effect of experimentally induced hyperinsulinemia on body composition
was studied in rats with food intakes precisely controlled by intragastric
feeding and physical activity manipulated by sedation with chlordiazepoxide
(CDP). Male Sprague-Dawley rats (n = 38) were fitted surgically with
gastrostomy tubes. After 8 days the animals were divided into four groups.
Group 1 received daily injections of protamine-zinc insulin; group 2
received daily injections of saline; group 3 received the same insulin
doses as group 1 plus daily administration of CDP mixed with the diet;
group 4 received daily injections of saline plus CDP in the diet. All
groups were tubefed identical amounts of semiliquid diet via gastrostomy.
Physical activity was measured by electronic monitor. After 4 wk the rats
were killed. The insulin-treated groups (1 and 3) had significantly larger
fat depots and larger mean fat cell size than the noninsulin-treated groups
(2 and 4). This increase in fat occurred concurrently with a decrease in
carcass protein and water. Physical activity, as measured, was unaltered by
insulin but was significantly reduced by CDP. Treatment with CDP only
increased the dorsal fat depot and liver weight but had no significant
effect on total dissected fat depots and had a reductive effect on carcass
protein. In conclusion insulin treatment enhanced the efficiency of
conversion of energy intake into fat energy stores.
