Polypeptides, pituitary hormones

Control of hormone synthesis and secretion in the anterior pituitary. Neurosecretory neurons in the hypothalamus liberate polypeptides that either stimulate or inhibit hormone synthesis by specialized pituitary cells containing the appropriate receptors. For example, GnRH stimulates gonadotroph cells in the pituitary to synthesize and secrete LH and FSH. These pituitary hormones then impinge on target cells, typically stimulating them to make other low-molecular-weight hormones. The end products of these cascades feedback-inhibit hormone production at either or both hypothalamic and pituitary levels. 

The classical parameters of >90% talc adsorption and TCA precipitation, with 3% agreement between the talc and TCA values, and <25% binding to resin are appropriate for polypeptide hormones with a certain chemical composition, including most anterior pituitary hormones. We have found, so far, two exceptions to the above parameters the S variant form of human growth hormone (hGH-S) and human FSH (all preparations). These are acidic proteins and show a decreased adsorption to talc and an increased binding to resin. 

Anterior pituitary hormones are classihed into three families the somatomammotropin family (GH and PRL), the glycoprotein hormones (LH, FSH, and TSH), and the opiomelanocortin family (ACTH, /i-endorphin, and related peptides). These three families appear to have evolved from three separate ancestral polypeptides homologous members of each family occur in other parts of the body. For example, human placental lactogen (hPL) is somatomammotropic, human chorionic gonadotrophin (hCG) is a glycoprotein hormone, and the brain and gut produce substances related to endorphins (enkephalins and dynorphin). 

GH is a pituitary hormone responsible for postnatal growth. Like all polypeptide hormones, GH was long thought to be circulating exclusively in the free form rather than being bound to plasma proteins, which was in contrast to some other... 

The greatest potassium loss occurs with the naturally occurring corticosteroids such as cortisone and hydrocortisone. Corticotropin (ACTH), which is a pituitary hormone, and tetracosactrin (a synthetic polypeptide) stimulate corticosteroid secretion by the adrenal cortex and can thereby indirectly cause potassium loss. Fludrocortisone also causes potassium loss. The synthetic corticosteroids (glucocorticoids) have a less marked potassium-depleting effect and are therefore less likely to cause problems. These include betamethasone, dexamethasone, prednisolone, prednisone and triamcinolone. 

However, insulin is not a very typical protein because of the shortness of its polypeptide chains and the -S-S- bridge which links residues 6 and 11 of the A chain. Similar loops containing six residues are found in the posterior pituitary hormones oxytocin and vasopressin, while one containing seven residues is found in calcitonin. Their special significance, if any, is not known. 

Small polypeptide hormones released by the hypothalamus which regulate the release of a specific pituitary hormone. They include ... 

A polypeptide hormone secreted by the anterior pituitary gland in both males and females. The highest serum levels occur in pregnancy, when, along with other hormones, it promotes lactation and mammary gland growth. Prolactin secretion, unlike other pituitary hormones, is limited by a hypothalamic prolactin-release inhibiting factor (PIF). 

CeUs synthesize and secrete multiple hormones. Eor example, some ceUs in the anterior pituitary have the capacity to secrete both polypeptide hormones, ESH and LH. CeUs also can secrete different chemical classes of hormone, eg, ceUs in the adrenal meduUa synthesize and secrete the... 

Human growth hormone (hGH) is a polypeptide with 191 amino acids. It is secreted by the pituitary gland. This hormone stimulates the production of insulin-like growth factor-1 (IGF-1) from the liver. Most of the positive effects of hGH are mediated by the IGF-1 system, which also includes specific binding proteins. 

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