Thyrotropin releasing hormone (TRH) is a tripeptide secreted by hypothalamus. Its physiological function is to release TSH stored in anterior pituitary cells through a series of ways, and increase TSH, T3 and T4 content in blood.TSH, T3 and T4 are measured at the same time as plasma TRH, so as to understand the cause of thyroid lesions, whether the lesions occur in thyroid or pituitary or hypothalamus.TRH has been successfully synthesized and applied in clinic.
(1) In primary hypothyroidism, TRH and TSH increased.In severe cases, the plasma TRH reached 3200pg/ml.(2) Secondary hypothyroidism can be caused by pituitary and hypothalamic diseases.Pituitary hypothyroidism, such as clinically common Sheehan syndrome, may also be normal with elevated TRH.Hypothalamic hypothyroidism reduces plasma TRH secretion, and the whole hypothalamic pituitary thyroid axis system functions poorly.(3) TRH is normal or decreased in hyperthyroidism, and it can also be increased.(4) In subacute thyroiditis, the blood TRH was normal in the early stage, and increased in the late stage when the thyroid was low.(5) Congenital single TRH deficiency is rare clinically.(6) There are many hormone changes in hypothalamic dysfunction, sometimes similar to hypothalamic hypothyroidism.
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Because of the high technical requirements for TRH determination, TRH excitation test is often used in clinical practice, and TSH detection is used to replace TRH determination.
