Aging blocks the thermoregulatory action of thyrotropin-releasing hormone in anaesthetized rats.

The influence of aging on the thermoregulatory effect of thyrotropin-releasing hormone (TRH) was studied in young (3-month-old) and aged (24-month-old) chloral hydrate-treated rats subjected either to normothermic (23 degrees C) or cold (4 degrees C) environment. Cerebroventricular injection of TRH (1 or 10 micrograms) or the TRH analog, CG 3509 (0.1 or 1 microgram), significantly enhanced the decline of body temperature in the young, anaesthetized rats, both in the normal and cold environments, but had no effect whatsoever on the decrease in body temperature in the chloral hydrate-treated aged animals. These results suggest that aging impairs the central mechanism(s) involved in the thermoregulatory action of TRH.