Linked Life Data

9048609

Source:http://linkedlifedata.com/resource/pubmed/id/9048609

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
3
pubmed:dateCreated
1997-4-7
pubmed:abstractText
Repeated stimulation of pituitary cell cultures with GH-releasing hormone (GHRH) results in diminished responsiveness, a phenomenon referred to as homologous desensitization. One component of GHRH-induced desensitization is a reduction in GHRH-binding sites, which is reflected by the decreased ability of GHRH to stimulate a rise in intracellular cAMP. In the present study, we sought to determine if homologous down-regulation of GHRH receptor number is due to a decrease in GHRH receptor synthesis. To this end, we developed and validated a quantitative RT-PCR assay system that was capable of assessing differences in GHRH-R messenger RNA (mRNA) levels in total RNA samples obtained from rat pituitary cell cultures. Treatment of pituitary cells with GHRH, for as little as 4 h, resulted in a dose-dependent decrease in GHRH-R mRNA levels. The maximum effect was observed with 0.1 and 1 nM GHRH, which reduced GHRH-R mRNA levels to 49 +/- 4% (mean +/- SEM) and 54 +/- 11% of control values, respectively (n = three separate experiments; P < 0.05). Accompanying the decline in GHRH-R mRNA levels was a rise in GH release; reaching 320 +/- 31% of control values (P < 0.01). Because of the possibility that the rise in medium GH level is the primary regulator of GHRH-R mRNA, we pretreated pituitary cultures for 4 h with GH to achieve a concentration comparable with that induced by a maximal stimulation with GHRH (8 micrograms GH/ml medium). Following pretreatment, cultures were stimulated for 15 min with GHRH and intracellular cAMP accumulation was measured by RIA. GH pretreatment did not impair the ability of GHRH to induce a rise in cAMP concentrations. However, as anticipated, GHRH pretreatment (10 nM) significantly reduced subsequent GHRH-stimulated cAMP to 46% of untreated controls. These data suggest that GHRH, but not GH, directly reduces GHRH-R mRNA levels. To determine whether this effect was mediated through cAMP, cultures were treated with forskolin, a direct stimulator of adenylate cyclase. Forskolin (10 microM) significantly reduced GHRH-R mRNA concentrations (37 +/- 6% of control values) indicating that GHRH acts through the cAMP-second messenger system cascade to regulate GHRH-R mRNA. The somatostatin analogue, octreotide (10 nM), which has been previously reported to decrease adenylate cyclase activity, did not affect GHRH-R mRNA levels. Taken together, these results indicate that GHRH inhibits the production of its own receptor by a receptor-mediated, cAMP-dependent reduction of GHRH-R mRNA accumulation.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
AIM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Mar
pubmed:issn
0013-7227
pubmed:author
pubmed:issnType
Print
pubmed:volume
138
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1058-65
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed-meshheading:9048609-Animals, pubmed-meshheading:9048609-Cells, Cultured, pubmed-meshheading:9048609-Culture Media, Serum-Free, pubmed-meshheading:9048609-Dexamethasone, pubmed-meshheading:9048609-Down-Regulation, pubmed-meshheading:9048609-Female, pubmed-meshheading:9048609-Forskolin, pubmed-meshheading:9048609-Growth Hormone-Releasing Hormone, pubmed-meshheading:9048609-Octreotide, pubmed-meshheading:9048609-Pituitary Gland, Anterior, pubmed-meshheading:9048609-Polymerase Chain Reaction, pubmed-meshheading:9048609-RNA, Messenger, pubmed-meshheading:9048609-Rats, pubmed-meshheading:9048609-Rats, Sprague-Dawley, pubmed-meshheading:9048609-Receptors, Neuropeptide, pubmed-meshheading:9048609-Receptors, Pituitary Hormone-Regulating Hormone, pubmed-meshheading:9048609-Transcription, Genetic
pubmed:year
1997
pubmed:articleTitle
Homologous down-regulation of growth hormone-releasing hormone receptor messenger ribonucleic acid levels.
pubmed:affiliation
Department of Medicine, University of Illinois at Chicago 60612, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't