Daily intervals of heat exposure alter the phase of the daily variation of plasma hormones in Holtzman rats.
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.
De Souza
C J
CJ
Department of Zoology and Physiology, Louisiana State University, Baton Rouge 70803.
Meier
A H
AH
D000064:Acclimatization; D000273:Adipose Tissue / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001833:Body Temperature Regulation; D002940:Circadian Rhythm; D003345:Corticosterone / Q000097:blood*; D004435:Eating; D005934:Glucagon / Q000097:blood*; D006358:Hot Temperature; D007328:Insulin / Q000097:blood*; D008297:Male; D011388:Prolactin / Q000097:blood; D051381:Rats; D015430:Weight Gain
D001786:Blood Glucose; D007328:Insulin; D011388:Prolactin; D005934:Glucagon; D003345:Corticosterone