Pituitary-adrenal function in rats chronically exposed to cold.
Exposure to cold for 2 weeks was used to assess the effects of a sustained stimulus on pituitary-adrenal function in male rats. The diurnal peak in plasma and adrenal corticosterone was advanced by 4 h during the first 24 h of exposure to cold but returned to its usual time (2000 h) by the next day. Plasma ACTH and corticosterone levels were generally greater at all times during the 24-h cycle in animals exposed to cold for up to 2 weeks, with the greatest increase occurring consistently at the time of peak. When rats exposed to cold for 1 week were returned to a normal 24 C environment, plasma corticosterone tended to increase. Plasma ACTH and plasma and adrenal corticosterone responses to a superimposed acute provocative stimulus (ip saline injection) were faster, greater, and more sustained in rats exposed to cold for 3 or 7 days. Similarly, the compensatory adrenal hypertrophy response to unilateral adrenalectomy was greater in cold-exposed rats. Such animals were also more resistant to pituitary-adrenal suppression by prednisolone. In contrast, there was no change in the sensitivity of the adrenal to exogenous ACTH. The results suggest that chronic exposure to cold causes a sustained activation of central mechanisms that regulate pituitary ACTH secretion as well as extra-pituitary mechanisms that regulate adrenal size; it reduces the effectiveness of negative feedback mechanisms, but does not alter those involved in the regulation of adrenal rhythmicity or adrenal sensitivity to ACTH.
D000311:Adrenal Glands / Q000032:analysis; D000324:Adrenocorticotropic Hormone / Q000032:analysis; D000818:Animals; D002940:Circadian Rhythm; D003080:Cold Temperature; D003345:Corticosterone / Q000032:analysis; D007031:Hypothalamus / Q000502:physiology; D008297:Male; D010913:Pituitary-Adrenal System / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013312:Stress, Physiological / Q000503:physiopathology
D000324:Adrenocorticotropic Hormone; D003345:Corticosterone