A hypercaloric load activates thermogenesis but decreases stress
responses in both the sympathetic and adrenocortical systems.
Strack, A. M., S. F. Akana, C. J. Horsley, and M. F. Dallman.
Department of Physiology, University of California, San Francisco,
San Francisco, CA 94143-0444
APStracts 3:0358R, 1996.
Caloric over-ingestion generates a sympathetically-mediated increase
in brown adipose tissue (BAT) thermogenesis; its effect on the
hypothalamo-pituitary-adrenal (HPA) axis is unknown. To determine
whether metabolic activation affects the HPA axis, male rats were
provided palatable sucrose ad lib. After 5 or 10d sucrose, BAT and
basal- and restraint-induced HPA variables were measured. Some rats
were instrumented with temperature probes. BAT temperature and HPA
axis responses to restraint were measured. Although caloric intake
increased at least 18%, body weight gain did not change after
sucrose; DNA, protein and uncoupling protein increased in BAT depots
and white adipose tissues were heavier after both 5 and 10d. During
d5-10, the BAT-core temperature difference was +0.30 C in sucrose
rats and -0.46 C in controls (p <0.05); this, together with
the biochemical changes, demonstrates persistent activation of BAT by
excess calories. Basal HPA measures were not altered. The sucrose
group exhibited smaller BAT temperature and HPA responses to
restraint on d10; there was no HPA difference on d5. We conclude that
calorically-mediated increases in BAT thermogenesis are independent
of basal HPA activity; however, both systems respond concordantly to
restraint stress. The diminished response to restraint in both
systems in sucrose-fed rats may result from signals indicating
increased energy stores. (217 words)
Received 9 February 1996; accepted in final form 28 August 1996.
APS Manuscript Number R85-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996