title: Growth hormone response to growth hormone-releasing peptide-2 in growth hormone-deficient little mice.
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.
  
  
  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.
authors.affiliation: Biotechnology Department, National Nuclear Energy Commission, Cidade Universitária, São Paulo, SP, Brazil.
authors.forename: Cibele N
authors.initials: CN
authors.lastname: Peroni
authors.forename: Cesar Y
authors.initials: CY
authors.lastname: Hayashida
authors.forename: Nancy
authors.initials: N
authors.lastname: Nascimento
authors.forename: Viviane C
authors.initials: VC
authors.lastname: Longuini
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Toledo
authors.forename: Paolo
authors.initials: P
authors.lastname: Bartolini
authors.forename: Cyril Y
authors.initials: CY
authors.lastname: Bowers
authors.forename: Sergio P A
authors.initials: SP
authors.lastname: Toledo
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D054439:Ghrelin / Q000097:blood; D013006:Growth Hormone / Q000172:deficiency / Q000378:metabolism*; D006579:Heterozygote; D020738:Leptin / Q000097:blood; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009842:Oligopeptides / Q000008:administration & dosage / Q000494:pharmacology*; D011897:Random Allocation; D018013:Receptors, Neuropeptide / Q000235:genetics*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000235:genetics*
chemical_list: D054439:Ghrelin; D020738:Leptin; D009842:Oligopeptides; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D013006:Growth Hormone; C091874:growth hormone-releasing peptide-2; C048250:somatotropin releasing hormone receptor