Peptide hypothalamic

CART (cocaine- and amphetamine-regulated transcript) is a hypothalamic peptide that inhibits both normal and starvation-induced feeding when injected into cerebral ventricles of rats. CART is co-localized with the anorexigenic peptide a-melanocyte-stimulating hormone in neurons of the arcuate nucleus. Secretion of CART is stimulated by leptin and CART may be an endogenous inhibitor of food intake. 

Date, Y., Ueta, Y., Yamashita, H. et al. (1999). Orexins, orexigenic hypothalamic peptides, interact with autonomic, neuroendocrine and neuroregulatory systems. Proc. Natl Acad. Sci. USA 96, 748-53. 

The synthesis and release of both FSH and LH from the pituitary is stimulated by a hypothalamic peptide, gonadotrophin-releasing hormone (also known as gonadorelin, LH-releasing hormone, or LH/FSH-releasing factor). 

Vale W, Spiess J, Rivier C, Rivier J (1981) Characterization of a 41 -residue ovine hypothalamic peptide that stimulates secretion of corticotropin and p-endorphin. Science 213 1394-1397... 

Vale A, Green S, Montgomery AM, Shall S (1998) The nitric oxide synthesis inhibitor L-NAME produces anxiogenic-like effects in the rat elevated plus-maze test, but not in the social interaction test. J Psychopharmacol 12 268-272 Vale W, Spiess J, Rivier C, Rivier J (1981) Characterization of a 41 -residue ovine hypothalamic peptide that stimulates secretion of corticotropin and p-endorphin. Science 213 1394-1397... 

Somatostatin (or somatotropin release-inhibiting factor [SRIF]) occurs primarily as a 14-amino acid peptide, although a 28-amino acid form also exists. As with the other hypothalamic peptides, it is formed by proteolytic cleavage of a larger precursor. Somatostatin, originally isolated from the hypothalamus, is also in many other locations, including the cerebral cortex, brainstem, spinal cord, gut, urinary system, and skin. Somatostatin inhibits the secretion of many substances in addition to growth hormone (Table 59.1). 

Another common mechanism for modulating hormonal response involves two (or more) hormonal inputs with both positive and negative effects (see fig. 24.21). The hypothalamic peptides, somatostatin and GRF, have opposite effects on GH synthesis and secretion. Similarly, glucagon and insulin have opposite effects on gluconeogenesis in the liver (see the discussion earlier in this chapter), and some of the effects of ecdysone on gene expression in insects are blocked by juvenile hormone (a terpene derivative fig. 24.22). 

Tu B, Timofeeva O, Jiao Y et al (2005) Spontaneous release of neuropeptide Y tonically inhibits recurrent mossy fiber synaptic transmission in epileptic brain. J Neurosci 25 1718-29 Ueda H, Fukushima N, Ge M et al (1987) Presynaptic opioid kappa-receptor and regulation of the release of Met-enkephalin in the rat brainstem. Neurosci Lett 81 309-13 van den Pol AN, Gao XB, Obrietan K et al (1998) Presynaptic and postsynaptic actions and modulation of neuroendocrine neurons by a new hypothalamic peptide, hypocretin/orexin. J Neurosci 18 7962-71... 

Specific dissection is performed on the brain and pituitary gland. Hypothalamic fragments may be dissected and shock frozen immediately in liquid nitrogen, for later extraction and determination of hypothalamic peptides. The pituitary gland is dissected, the posterior pituitary is stored separately, and the anterior pituitary is halved by a median-sagittal cut to obtain separate tissue samples for histology (fixation), and for subsequent analysis of hormone contents (stored frozen at -20 °C until hormone assay). 

Many tests substances change the secretion of hypothalamic hormones, either by direct action or more generally by a feedback effects at the hypothalamic level. Under these conditions, the tissue concentration in hypothalamic specimens of treated rats is of interest, especially because several hypothalamic peptide assays are available and can be measured in the same specimen. In contrast to the tissue concentration, for many hypothalamic hormones it is difficult to measure the circulating concentrations, due to analytical problems of low concentration and rapid inactivation by enzymes. Circulating concentrations would also change immediately due to the interference of anesthesia and of the autopsy procedure. It is therefore recommended to take samples of hypothalamic tissue, and control samples of cerebral cortical tissue. 

The peptide concentration in the individual specimens is determined by radioimmunoassay, using a synthetic reference peptide for the standard curve. Several commercial assays are now available for hypothalamic peptides. An alternative method is the determination of peptide content in tissue extracts by an HPLC method or by mass spectrometry. 

Vigh S, Schally AV (1984) Interaction between hypothalamic peptides in a superfused pituitary cell system. Peptides 5(Suppl I) 241-247... 

CRH activity, by determination of the hypothalamic peptide content - the information obtained by this measurement is usually limited and and will be controlled by the feedback action of pituitary hormone release or inhibition and adrenal steroid secretion... 

The anterior pituitary releases GH in 6 to 8 pulsatile bursts over a 24 h period the major portion is released just prior to deep sleep. Its secretion is controlled by hypothalamic peptides GH-releasing hormone stimulates GH secretion, while somatostatin inhibits it. GH stimulates the synthesis of insulin-like growth factor-1 (IGF-1 somatomedin C) mainly, but not solely, in the liver. GH and IGF-1 receptors are widely scattered throughout the body, and both hormones exert important metabolic actions in various tissues, especially muscle and bone. 

Bnrgns R, Ling N, Bntcher M, Gnillemin R. Primary stmctnre of somatostatin, a hypothalamic peptide that inhibits the secretion of pitnitary growth hormone. Proc. Nat. Acad. Sci. U.S.A. 1973 70 684-688. 

Carraway R, Leeman SE. Amino acid sequence of a hypothalamic peptide, neurotensin. J. Biol. Chem. 1975 250 1907-1911. 

GH-secreting pituitary tumors account for most of the cases of acromegaly. Patients who have pituitary tumors that produce GH are frequently shown to release GH in response to other hypothalamic peptides (TRH and Gn-RH) that... 

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