Administration of low doses of TSH result in a rapid increase in the metabolic rate of young lambs.

: A low dose of TSH (Thyroid Stimulating Hormone) can induce a rapid increase in VO2 and the response is dose dependent. Lambs aged 36 to 289 h were used. 5.0 i.u./kg TSH, the highest dose used, caused an initial inhibition of response but during the second and third post injection hours VO2 increased to control level. The intermediate TSH dose, 1.0 i.u./kg TSH resulted in a clear increase in VO2 even in the first post-injection hour, which further increased in the second and third hours. This change was significantly greater than in controls. Animals treated with the lowest dose, 0.5 i.u./kg TSH divided themselves into 2 distinct populations: responders, where an immediate and significant increase in VO2 occurred and non responders, where a small inhibition of metabolism was evident. The responder group had a significantly lower pre-injection VO2 and a significantly lower mean body weight, than the non responders. In the responders, the stimulation of metabolism was greater than at either of the higher TSH doses. These results indicate that low, but not high doses of TSH induce a rapid metabolic response. The argument in favour of a short-term role for thyroid hormones is thus strengthened.