Abstract

Thyrotrophin-releasing hormone (TRH - Roche) is a synthetic tripeptide, L-pyroglutamyl-L-histidyl-L-proline-amide, which is identical with the porcine, ovine and human hypothalamic hormone that promotes the secretion of thyrotrophin. Secreted in the hypothalamus, it passes down the capillaries of the pituitary stalk to the anterior pituitary and there causes release of thyrotrophin. Thyroid hormones (triiodo-thyronine (T₃) and thyroxine (T₄)) interfere with the thyrotrophin (TSH)-releasing action of TRH, so that excess thyroid hormones block TSH release in response to TRH; conversely when thyroid hormone levels are low, increased secretion of TSH occurs. The hypothalamic secretion of TRH is probably directly influenced by the concentration of thyroid hormones in the blood reaching it. In addition TRH promotes the secretion of prolactin from the pituitary. TRH-Roche is marketed in Britain for use in hospitals in diagnostic tests of thyroid and of pituitary-hypothalamic function.