Reed H L, Quesada M, Hesslink R L, D'Alesandro M M, Hays M T, Christopherson R J, Turner B V, Young B A
Department of Medicine, Endocrine Service, Madigan Army Medical Center, Tacoma, Washington 98431-5000.
Am J Physiol. 1994 May;266(5 Pt 1):E786-95. doi: 10.1152/ajpendo.1994.266.5.E786.
Swine exposed to cold air have elevated serum values of total triiodothyronine (TT3) and free T3 (FT3). To characterize the mechanism of these increases, we measured in vivo kinetic parameters after a bolus intravenous injection of 125I-labeled T3 by use of both multicompartmental (MC) and noncompartmental (NC) methods and in vitro hepatic type I iodothyronine 5'-deiodinase (5'D-I) activity. Ten ad libitum-fed 5-mo-old boars were divided into two groups, living for 25 days in either control (22 degrees C) or cold (4 degrees C) conditions. Cold-exposed animals consumed 50% more calories than control animals but showed no difference in total body weight, percent body fat, or plasma volume. Thyroid gland weight was increased 86% (P < 0.004), as was serum total thyroxine (TT4) (48%), free T4 (FT4) (61%), TT3 (103%), and FT3 (107%), whereas serum thyrotropin (TSH) was not different in cold-exposed compared with control animals. The T3 plasma clearance rate was similar between groups when both MC and NC techniques were used. However, T3 plasma appearance rate (PAR) was elevated in cold-treated animals 110% over controls by MC (P < 0.001) and 83% by NC methods (P < 0.001). The animal total hormone pool of T3 was increased 76% (MC) and 53% (NC) compared with control (P < 0.01). The Michaelis constant of hepatic 5'D-I was not different between groups, but the maximum enzyme velocity increased (106%; P < 0.02). Therefore cold exposure for 25 days is associated with increased energy intake, thyroid size, T3 PAR, and hepatic 5'D-I activity with little change in serum TSH.
暴露于冷空气的猪血清总三碘甲状腺原氨酸（TT3）和游离T3（FT3）值升高。为了阐明这些升高的机制，我们通过多室（MC）和非房室（NC）方法，在静脉推注125I标记的T3后测量体内动力学参数，并检测体外肝I型碘甲状腺原氨酸5'-脱碘酶（5'D-I）活性。将10头5月龄自由采食的公猪分为两组，分别在对照（22℃）或寒冷（4℃）条件下饲养25天。寒冷暴露的动物比对照动物多消耗50%的热量，但总体重、体脂百分比或血浆量无差异。甲状腺重量增加86%（P<0.004），血清总甲状腺素（TT4）增加48%（P<0.004），游离T4（FT4）增加61%（P<0.004），TT3增加103%（P<0.004），FT3增加107%（P<0.004），而寒冷暴露动物的血清促甲状腺激素（TSH）与对照动物相比无差异。当使用MC和NC技术时，两组之间的T3血浆清除率相似。然而，通过MC方法，寒冷处理动物的T3血浆出现率（PAR）比对照升高110%（P<0.001），通过NC方法升高83%（P<0.001）。与对照相比，动物T3的总激素池增加76%（MC）和53%（NC）（P<0.01）。两组之间肝5'D-I的米氏常数无差异，但最大酶活性增加（106%；P<0.02）。因此，25天的寒冷暴露与能量摄入增加、甲状腺大小、T3 PAR和肝5'D-I活性增加相关，而血清TSH变化不大。
