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Subject: Corticotropin-Releasing Hormone (CRH)
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CRH is a 41-amino-acid peptide hypothalamic factor that increases ACTH release from pituitary cells. CRH is synthesized by neurons in the parvocellular division of the hypothalamic paraventricular nuclei. The axons of the nuclei project to the median eminence, where CRH is secreted into the hypophyseal portal blood. The ACTH released by CRH stimulates the secretion of cortisol and other adrenal steroids, such as DHEA and, transiently, aldosterone. CRH circulates in human plasma bound to a high-affinity binding protein, which reduces its bioactivity and increases its clearance. In addition to being produced in the hypothalamus, CRH is also synthesized in peripheral tissues, such as T lymphocytes, and is highly expressed in the placenta. In the placenta, CRH is a marker that determines the length of gestation and the timing of parturition and delivery. Other names: corticoliberin, corticotropin-releasing factor (CRF).
Normal range: up to 10 pg/mL.
To exclude the possibility of an extrapituitary CRH-secreting tumor
Ectopic tumors producing ACTH
Third trimester of pregnancy
Autosomal recessive hypothalamic corticotropin deficiency
The patient should be fasting 10–12 hours and should not take any corticosteroid, ACTH, or estrogen medications, if possible, for at least 48 hours prior to collection of specimen. An am specimen is preferred. This test is rarely used.
A rapid increase in circulating levels of CRH occurs at the onset of parturition.
Plasma CRH concentrations do not correlate with plasma ACTH or serum cortisol concentrations or with altered hypothalamic–pituitary–adrenal axis function (e.g., in primary adrenal insufficiency or Cushing syndrome, or during insulin-induced hypoglycemia or metyrapone administration). Some investigators have reported a correlation between plasma CRH and plasma ACTH or serum cortisol in pregnancy, but others have not.
The contribution of hypothalamic CRH to peripheral plasma CRH concentrations is small; most of the plasma CRH presumably comes from nonhypothalamic sources.
However, under certain circumstances, such as insulin-induced hypoglycemia or during major surgery, small increments in plasma CRH concentrations may reflect hypothalamic CRH release.