AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 5 1115-R1120, Copyright © 1993 by American Physiological Society
Daily intervals of heat exposure alter the phase of the daily variation of plasma hormones in Holtzman rats
C. J. De Souza and A. H. Meier
Department of Zoology and Physiology, Louisiana State University, Baton Rouge 70803.
The effects of timed daily increases in ambient temperature (thermopulses)
(from 22 +/- 1 to 40 +/- 1 degree C for 2 h) on daily variations of
hormones involved in glucose and lipid metabolism were tested in male
Holtzman rats (3-4 mo old) exposed to a 12-h daily photoperiod. The
thermopulses were administered for 14 days either at light onset (TP0) or
16 h after light onset (TP16). Body weights and food consumption were
monitored during the experiment. Retroperitoneal fat weights and plasma
concentrations of insulin, glucose, glucagon, corticosterone, and prolactin
were determined from blood taken every 4 h during a 24-h period commencing
24 h after the last thermopulse. TP0 treatment did not alter any of the
parameters tested. Conversely, TP16 treatment obliterated the daily rhythms
of insulin and corticosterone present in the controls (nonthermopulsed) and
decreased body weight gains, retroperitoneal fat stores, food consumption,
and the baseline levels of plasma insulin and corticosterone. The present
study supports a role for circadian neuroendocrine rhythms in the reduction
of fat stores induced by properly timed daily thermopulses.
