Central thyrotropin-releasing hormone infusion opposes cardiovascular and metabolic suppression during caloric restriction.
Inhibition of hypothalamic thyrotropin-releasing hormone (TRH) neuronal activity is a well-established adaptation to caloric restriction (CR) that suppresses pituitary secretion of thyroid-stimulating hormone, but may also participate in modulation of autonomic function. Thus, we hypothesized that decreased hypothalamic TRH activity contributes to CR-induced bradycardia and decreased metabolic rate. To test this hypothesis, male Sprague-Dawley rats were instrumented with telemetry devices for measurement of heart rate (HR) and blood pressure (BP) and a lateral intracerebroventricular (i.c.v.) guide cannula for central infusions. After recovery, rats were housed in metabolic chambers and given either ad libitum(ad-lib) or CR treatments for 7 days; half of each diet group was then given continuous i.c.v. infusions of TRH (25 nmol/h) or saline (0.25 microl/h) for 7 days via osmotic pump. This dose of TRH did not significantly alter peripheral free T(4) levels. In ad-lib rats, TRH infusion produced small reductions in food intake and small increases in HR and BP over saline-infused controls. In CR rats, TRH infusion resulted in an increase in HR and also energy expenditure over saline-infused controls. These results support the hypothesis that suppression of central TRH activity contributes to the homeostatic suppression of energy expenditure and HR observed during CR.
Knight
W David
WD
Program in Neuroscience, Florida State University, Tallahassee, 32306-4340, USA.
Swoap
Steven J
SJ
Parsons
Almetra D
AD
Overton
J Michael
JM
D000704:Analysis of Variance; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D031204:Caloric Restriction; D002319:Cardiovascular System / Q000187:drug effects*; D004333:Drug Administration Routes; D004334:Drug Administration Schedule; D004435:Eating / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D007276:Injections, Intraventricular / Q000379:methods; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D011863:Radioimmunoassay / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage* / Q000097:blood
D013973:Thyrotropin-Releasing Hormone