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      Growth hormone response to growth hormone-releasing peptide-2 in growth hormone-deficient Little mice

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          Abstract

          OBJECTIVE:

          To investigate a possible direct, growth hormone-releasing, hormone-independent action of a growth hormone secretagogue, GHRP-2, in pituitary somatotroph cells in the presence of inactive growth hormone-releasing hormone receptors.

          MATERIALS AND METHODS:

          The responses of serum growth hormone to acutely injected growth hormone-releasing P-2 in lit/lit mice, which represent a model of GH deficiency arising from mutated growth hormone-releasing hormone-receptors, were compared to those observed in the heterozygous (lit/+) littermates and wild-type (+/+) C57BL/6J mice.

          RESULTS:

          After the administration of 10 mcg of growth hormone-releasing P-2 to lit/lit mice, a growth hormone release of 9.3±1.5 ng/ml was observed compared with 1.04±1.15 ng/ml in controls ( p<0.001). In comparison, an intermediate growth hormone release of 34.5±9.7 ng/ml and a higher growth hormone release of 163±46 ng/ml were induced in the lit/+ mice and wild-type mice, respectively. Thus, GHRP-2 stimulated growth hormone in the lit/lit mice, and the release of growth hormone in vivo may be only partially dependent on growth hormone-releasing hormone. Additionally, the plasma leptin and ghrelin levels were evaluated in the lit/lit mice under basal and stimulated conditions.

          CONCLUSIONS:

          Here, we have demonstrated that lit/lit mice, which harbor a germline mutation in the Growth hormone-releasing hormone gene, maintain a limited but statistically significant growth hormone elevation after exogenous stimulation with GHRP-2. The present data probably reflect a direct, growth hormone-independent effect on Growth hormone S (ghrelin) stimulation in the remaining pituitary somatotrophs of little mice that is mediated by growth hormone S-R 1a.

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          Most cited references118

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          A receptor in pituitary and hypothalamus that functions in growth hormone release.

          Small synthetic molecules termed growth hormone secretagogues (GHSs) act on the pituitary gland and the hypothalamus to stimulate and amplify pulsatile growth hormone (GH) release. A heterotrimeric GTP-binding protein (G protein)-coupled receptor (GPC-R) of the pituitary and arcuate ventro-medial and infundibular hypothalamus of swine and humans was cloned and was shown to be the target of the GHSs. On the basis of its pharmacological and molecular characterization, this GPC-R defines a neuroendocrine pathway for the control of pulsatile GH release and supports the notion that the GHSs mimic an undiscovered hormone.
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            Genealogies of mouse inbred strains.

            The mouse is a prime organism of choice for modelling human disease. Over 450 inbred strains of mice have been described, providing a wealth of different genotypes and phenotypes for genetic and other studies. As new strains are generated and others become extinct, it is useful to review periodically what strains are available and how they are related to each other, particularly in the light of available DNA polymorphism data from microsatellite and other markers. We describe the origins and relationships of inbred mouse strains, 90 years after the generation of the first inbred strain. Given the large collection of inbred strains available, and that published information on these strains is incomplete, we propose that all genealogical and genetic data on inbred strains be submitted to a common electronic database to ensure this valuable information resource is preserved and used efficiently.
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              Dwarf locus mutants lacking three pituitary cell types result from mutations in the POU-domain gene pit-1.

              Mutations at the mouse dwarf locus (dw) interrupt the normal development of the anterior pituitary gland, resulting in the loss of expression of growth hormone, prolactin and thyroid-stimulating hormone, and hypoplasia of their respective cell types. Disruptions in the gene encoding the POU-domain transcription factor, Pit-1, occur in both characterized alleles of the dwarf locus. The data indicate that Pit-1 is necessary for the specification of the phenotype of three cell types in the anterior pituitary, and directly link a transcription factor to commitment and progression events in mammalian organogenesis.
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                Author and article information

                Journal
                Clinics (Sao Paulo)
                Clinics
                Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo
                1807-5932
                1980-5322
                March 2012
                : 67
                : 3
                : 265-272
                Affiliations
                [I ]Biotechnology Department, National Nuclear Energy Commission (IPEN-CNEN), Cidade Universitária, São Paulo/SP, Brazil.
                [II ]Faculdade de Medicina da Universidade de São Paulo, Department of Medicine, Endocrinology, Endocrine Genetics Unit/LIM 25, São Paulo/SP, Brazil.
                [III ]Tulane University Health Sciences Center, Department of Medicine, Division of Endocrinology, Endocrine Section, New Orleans, LA/USA.
                Author notes

                Peroni CN, Nascimento N, and Bartolini P performed the experiments and collaborated in the manuscript preparation. Hayashida CY collaborated in the manuscript writing. Toledo RA and Longuini VC performed the genetic analyses. Bowers CY collaborated with the product testing (ghrp-2), the measurements of ghrelin and leptin and the preparation of the manuscript. Toledo SP wrote and coordinated the research project and was the senior researcher responsible for preparing the manuscript.

                E-mail: toldo@ 123456usp.br Tel.: 55 11 3133.9694
                Article
                cln_67p265
                10.6061/clinics/2012(03)11
                3297037
                22473409
                1a0968c2-ddc4-4bdc-95b7-c0fd31e2ba5f
                Copyright © 2012 Hospital das Clínicas da FMUSP

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 16 November 2011
                : 22 November 2011
                : 15 December 2011
                Page count
                Pages: 8
                Categories
                Basic Research

                Medicine
                little mouse,leptin,ghrp-2,gh,ghrelin,ghrh-r
                Medicine
                little mouse, leptin, ghrp-2, gh, ghrelin, ghrh-r

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