title: Maturation of hypothalamic-pituitary-thyroid response in the rat to acute cold.
abstract: Groups of rats 3, 4, 5, 7, and 10 wk of age were tested for their ability to respond to acute cold (4 degrees C for 30 min). Thyroid reactions were estimated from intrathyroidal colloid droplet (CD) counts, serum thyrotropin (TSH) and thyroxine (T4) levels. Normally CD counts increased to a maximum in the 5-wk-old rats were lower in the 7-wk-old, and still lower in the 10-wk-old animals. The significant finding was that exposure to cold caused a decrease in CD counts in 3-, 4-, 5-wk-old rats but an increase in mature animals. This CD decrease was apparent within 10 min in the 4- and 5-wk-old rats, Injections of TSH and thyrotropin-releasing hormone (TRH) raised CD counts in all age groups but had little effect on response to cold. TSH serum levels were higher in the 5-wk-old than in the 3- and 4-wk-old animals; cold caused a greater TSH reduction in the 5-wk-old rats than in younger groups. Serum T4 levels were approximately the same in 3-, 4-, and 5-wk-old rats; when they were exposed to cold, the level rose despite the fact that CD counts dropped. These data indicate that in rats hypothalamic-pituitary-thyroid reactions to acute cold attain the adult pattern between 5 and 7 wk after birth.
mesh_terms: D000222:Adaptation, Physiological; D000375:Aging; D000818:Animals; D003080:Cold Temperature; D007031:Hypothalamus / Q000502:physiology*; D008297:Male; D010902:Pituitary Gland / Q000502:physiology*; D051381:Rats; D013961:Thyroid Gland / Q000378:metabolism / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D013972:Thyrotropin; D013974:Thyroxine