Thyrotropin releasing hormone

TRH, also called "thyrotropin releasing hormone", is a peptide hormone produced in the hypothalamus. TRH is produced under the influence of the nucleus suprachiasmaticus from its precursor, pro-thyrooliberin. The release of TRH follows a circadian rhythm with maximum release around midnight and minimum release in the late afternoon.

TRH is transported via the hypothalamic-pituitary portal vein system to the anterior lobe of the pituitary (adenohypophysis). There the peptide hormone stimulates the formation and release of prolactin and TSH. Thus TRH also indirectly stimulates the release of the thyroid hormones T4 and T3 in the thyroid gland via TSH. However, TRH seems to be only to a small extent under the feedback control of T3 and T4.

The half-life of TRH is about 2 minutes. It is degraded by enzymatic cleavage by the metallopeptidase thyroliberinase.

TRH and thermoregulation: The release of TRH is stimulated by a reduction in body temperature, among other things. A TSH and subsequent T4 release rapidly stimulates the metabolism, causing the body temperature to rise again. Other energy-consuming mechanisms also stimulate the release of TRH.

Furthermore, TRH is involved in the suppression of pain, in the sleep-wake-regulation and in the braking of food and fluid intake.