Abstract
Summary
Significant TRH-like activity was detected in the blood of thyroidectomized-hypophysectomized rats after (but not before) exposure to mild cold. Thus mild cold is capable of acting as a specific stimulus for the release of TRH in rats. This provides the first evidence for the possible physiologic importance of TRH. A study was made of the conditions under which TRH can be detected in blood. The presence of TRH in the peripheral circulation may be dependent upon the levels of the enzyme(s) responsible for its destruction. TRH is not detectable in the peripheral circulation unless the endogenous level of thyroid hormones is sufficiently reduced. Thyroid hormones are able to influence the levels or activity of the enzyme(s) responsible for the inactivation of TRH.
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