The Response of the Heterotopic Pituitary to Thyrotropin Releasing Hormone (TRH)

Abstract

The ability of pituitary glands grafted beneath thekidney capsule to mediate a discharge of ¹²⁵I from the thyroid gland in response to i. v. injections of TRH was evaluated by blood ¹²⁵I measurements. The minimum effective dose (3.3 ng TRH/rat) was less than that found for rats with intact pituitaries under the same conditions (10 ng TRH/rat). At higher dose levels the intact rats gave bigger responses than did rats with heterotopic pituitaries. The heterotopic pituitary retains its sensitivity to the releasing action of TRH but the magnitude of its responses is limited by the small amount of TSH available for release.