Regulation of thyrotrophin secretion.

Substantial advances in understanding the regulation of thyrotrophin (TSH) secretion have been made during the past decade. The hypothalamic tripeptide, thyrotrophin-releasing hormone, is the major stimulator of TSH secretion, and thyroid hormones exert the major inhibitory influences on TSH secretion. Other hypothalamic peptides, biogenic amines and steroid hormones modulate TSH secretion. Basal serum TSH measurement is mainly of value in diagnosing primary hypothyroidism, but because the lower limit of the normal range of TSH is not clearly defined, dynamic measurements of TSH secretion are used in preference to basal measurements in assessing other disorders of the hypothalamopituitary-thyroid axis.