Responses of core and peripheral temperatures to chronic cold stress in transiently goitrous goats

Thyroid hormones play a major role in controlling basal metabolic rate, body temperature and hemodynamics. Responses of core and peripheral body temperatures to transient use of thyreostatic drugs are seldom measured simultaneously under chronic experimental settings. We developed a technique to attain this goal. Eighteen Damascus goat kids (initial Avg. BW=44±0.7 kg) underwent a minor invasive surgical procedure to implant two miniature temperature data loggers, intraperitoneally and subcutaneously, to assess core (Tcore) and subcutaneous (Tsq) temperature changes when subjected to chronic (47 days) cold (< 10 °C) environment along with or without oral administration of the reversible goitrogen 6-N-propyl-2-thiouracil (PTU; 20 mg/kg BW/day). Nine animals served as controls whereas the remaining nine were treated with PTU for 31 out of total 47-day trial period. The PTU treatment significantly (P<0.05) depressed circulating free thyroxine (FT4), followed by a rebound after termination. Prior to initiation of PTU treatment, all animals displayed similar daily means of Tcore and Tsq. Subsequently, both temperatures precipitously declined (P<0.01) with the gradual drop in ambient temperature (Ta) overtime. However, PTU caused an immediate and further drop in Tsq, suggesting a reduction in cutaneous perfusion. Interestingly, on the other hand, a delayed downregulation of Tcore by PTU occurred 14 days post-treatment, indicating a relatively slower depression in metabolic thermogenesis after suppression of circulating thyroxine. Upon termination of PTU, Tcore but not Tsq, returned to simulate control levels. Results from the current study show the practicality of our technique to concurrently record core and peripheral temperatures in chronically-instrumented animals, and that PTU causes a marked depression in thermoregulatory ability during cold stress with no indication for a reduction in the temperature set-point.