Effect of synthetic thyrotrophin-releasing factor on pituitary TSH secretion in normal subjects and patients with hypothalamic-pituitary disorders.

Abstract

ABSTRACT Different doses of thyrotrophin-releasing factor (TRF) were administered by three different routes (intravenous, subcutaneous and oral) to 87 normal subjects in order to standardize the "TRF test" for the pituitary TSH reserve. The results were: 1) Intravenous single injection may be suitable as a routine TRF test because of the stability of TSH response to TRF and the reliability of TRF administration. 2) The maximum TSH increases were dose-related between 50 and 400 μg, so that we can recommend the use of 50 μg of TRF as a screening test for TSH secretion. 3) Oral administration and slow intravenous infusion of TRF with estimation of thyroxine levels can be useful as an indirect test of pituitary TSH reserve when TSH assays are not available. According to these results, the TRF test was performed in patients with hypothalamic-pituitary disorders. A normal increase in plasma TSH occurred in 10 out of 20 patients with operated pituitary chromophobe adenoma following the administration of 50 or 100 μg of TRF. Two patients showed no rise in plasma TSH after receiving 50 or 100 μg of TRF but a normal rise after receiving 400 or 600 μg of TRF. Little or no rise in the plasma TSH levels occurred following the administration of 100 μg TRF in pituitary chromophobe adenoma and Sheehan's syndrome who had a long standing pituitary insufficiency and secondary hypothyroidism. However, some cases with craniopharyngioma and pinealoma, accompanied with a low level of thyroid function, showed a normal TSH responses to 50 μg of TRF. Since the pituitary of these cases remained intact from tumour invasion, they should be assumed to have tertiary (hypothalamic) hypothyroidism. Of particular interest is the fact that the patients with suprahypophyseal tumour surprisingly showed a supernormal TSH response to 50 μg of TRF.