The hypothalamic pituitary thyroid axis: studies on the regulatory role of thyrotropin releasing hormone (TRH) (Japanese)

Abstract

When normal persons are given TRH p.o., the TSH response is blunted after successive doses but serum T3 and T4 levels increase progressively reaching their peak levels on the fourth day. In primary hypothyroidism despite a striking increase in circulating TSH after the chronic administration of TRH p.o., no thyroidal response is demonstrable. This finding raises the possibility of a short negative feedback loop, involving hypothalamic TRH and pituitary TSH synthesis and/or release. Some cases of secondary hypothyroidism demonstrate a thyroidal response to TRH p.o. in the absence of a demonstrable elevation in serum TSH following TRH p.o. and TRH IV. This suggests that TRH p.o. may permit a more definitive functional separation of the 3 varieties of hypothyroidism than TRH IV.