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(also releasing hormone), one of a group of neurohormones formed in the hypothalamus that act on the cells of the anterior lobe of the pituitary gland and stimulate or inhibit the secretion of tropic hormones into the blood. Extracts from the hypothalamus of humans and many vertebrate animals have been shown to contain specific releasing factors that stimulate the pituitary gland to release adrenocorticotropic hormone, luteinizing hormone, thyrotropin, folliclestimulating hormone, growth hormone, melanocyte-stimulating hormone, and prolactin. Releasing factors that inhibit the secretion of prolactin, melanocyte-stimulating hormone, and growth hormone have also been isolated.
All releasing factors appear to be peptides. For example, the releasing factor that stimulates the secretion of thyrotropin is a tripeptide—pyroglutamylhistidylpropylamide. This factor has been synthesized and is now used in medicine to detect local disorders of the hypothalamus, pituitary, and thyroid glands.
REFERENCESIudaev, N. A., and Z. F. Evtikhina. “Sovremennye predstavleniia o gipotalamicheskikh rilizing-faktorakh.” In Sovremennye voprosy endokrinologii, fase. 4. Moscow, 1972.
“Hypophysiotropic Hormones of the Hypothalamus: Assay and Chemistry.” Proceedings of the Workshop Conference…. Baltimore, 1970.
V. M. SAMSONOVA