Action of Hypothalamus-pituitary-thyroid Axis on Thermogenesis in Mongolian Gerbil (Meriones unguiculatus) Exposed to Cold

By mensurating thyrotropin-releasing-hormone (TRH) content in hypothalamus and median eminence (ME),T4,T3 and norepinephrine (NE) concentration in serum,and T45 deiodinase activity in brown adipose tissue (BAT),regulative mechanism of BAT thermogenesis was investigated in adult male Mongolian gerbils (Meriones unguiculatus),which randomly divided into three groups that control group kept in room temperature of (24±2)℃,and acute and chronic cold exposed groups kept in (4±1)℃ for 1 day and 3 weeks respectively.When animals were put into acute cold condition,their TRH content in hypothalamus decreased while that in ME arose,and T3 and NE concentration in serum and T45 deiodinase activity in BAT increased while T4 concentration in serum decreased compared with those in control group.Animals having been exposed to cold for 3 weeks,their TRH content in hypothalamus restored to the normal level,while TRH content in ME,T3 level in serum and T45 deiodinase activity in BAT were higher and T4 level in serum was lower than those in acute cold exposure group,and NE concentration in serum was still higher than that of control animals although it showed a decrease tendency as compared with acute cold exposed animals.It suggested that the cold exposure might activate the procedure of synthesis and secretion of hormones in hypothalamus-pituitary-thyroid (HPT) axis and the sympathetic nerve system in Mongolian gerbil,which brought on the occurrence of heat production for responding to changes of environmental temperature.