Low Doses of T₃ Induce a Rapid Metabolic Response in Young Lambs

Summary

Injection of 1 μg/kg T₃ resulted in an increase in metabolic rate (VO₂) within an hour of administration to lambs (aged 27 to 180 h). A larger dose of 5 μg/kg T₃ initially caused a slight inhibition of VO₂, which was followed in the second post-injection hour by a significant increase. The increase in VO₂ during the second post-injection hour after either 1 μg/kg or 5 μg/kg T₃ represented a rise of 22% above pre-injection VO₂. The increase persisted and was slightly enhanced during the third post-injection hour. These changes were significantly greater than the smaller changes which followed control injection (P < 0.005). No significant changes in T_re or T_esk occurred after any treatment. This rapid response to low, physiological doses of T₃ emphasises a possible role for thyroid hormones in the short-term control of metabolism in young animals.

Key-Words:

Triiodothyronine (T ₃ ) - Rapid Response - Physiological Doses - Metabolic Rate(VO ₂ ) - Newborn Lambs