BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 15. INTEGRATION OF METABOLIC PATHWAYS. HORMONES

15.5. Hypothalamic Hormones

R. Guillemin and A. Schally were the first to isolate pure substances from the Hypothalamus capable of regulating pituitary Functions and determined their chemical Structure. These substances were initially named neurohormones, and later releasing factors. This breakthrough led to the establishment of a unified hypothalamo-pituitary system, in which the secretion of substances at the hypothalamic level either stimulates or inhibits the release of tropic Hormones by the anterior pituitary.

Chemically, all releasing hormones—liberins and statins—are oligopeptides containing Amino Acids atypical of standard Proteins, such as pyroglutamic acid, prolinamide, and glycinamide. To date, The structure of several Hypothalamic hormones has been elucidated, including corticoliberin, thyroliberin, gonadoliberin, somatoliberin, and Somatostatin.

Thyroliberin, or thyrotropin-releasing hormone, is a tripeptide synthesized predominantly in the Neurons of the medial paraventricular nuclei of the hypothalamus. The active hormone is generated via the partial proteolysis of an inactive precursor. Thyroliberin stimulates the Synthesis and Secretion of thyroid-stimulating hormone and prolactin in the anterior pituitary:

Gonadoliberin, or gonadotropin-releasing hormone, is a decapeptide (Pyro-Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) synthesized in the neurons of the preoptic nuclei of the hypothalamus. It stimulates the synthesis and secretion of gonadotropic hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The precursor of human gonadoliberin is a polypeptide comprising 92 amino acid residues. Signal Transduction for gonadoliberin is mediated through the Inositol phosphate system.

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Corticoliberin, or corticotropin-releasing hormone, is synthesized in the neurons of the preoptic nuclei of the hypothalamus and stimulates the synthesis of POMC and The production of adrenocorticotropic hormone (ACTH) in the anterior pituitary. The corticoliberin receptor is a component of the adenylate cyclase complex.

Somatoliberin, or Growth Hormone-releasing hormone, stimulates the secretion of growth hormone by the adenohypophysis, whereas somatostatin inhibits it. Somatoliberin consists of 44 amino acid residues, while somatostatin comprises 14 and features a cyclic structure stabilized by a disulfide bond. Research has shown that somatostatin is produced not only in the hypothalamus but also in other regions of The Nervous system and the gastrointestinal tract. Somatostatin inhibits the secretion of numerous hormones, including Insulin, Glucagon, and gastrin.