Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Desensitization of rat pituitary somatotrophs to human growth hormone-releasing factor (hGHRF) was investigated using cultured rat anterior pituitary cells. Growth hormone (GH) release decreased but the production of cAMP was still induced in response to subsequently added 10(-9) M hGHRF from cells pretreated with hGHRF at concentrations ranging from 10(-11) to 10(-7) M for 4 h. Desensitization to 10(-9) M hGHRF was also observed in cells pretreated with 10(-9) M hGHRF for 4 h in the presence of 2 mM EGTA, 10 ng/ml nifedipine or 10(-9) M somatostatin-28, which decreased GH release during pretreatment. Forskolin and A23187, at concentrations of 10(-6) M and 10(-4) M, respectively, stimulated GH release from cells pretreated with hGHRF to the same extent as that from the control cells. These results, therefore, suggest that desensitization to GHRF occurs regardless of the presence of releasable GH pool and that some changes such as uncoupling of GHRF receptors with adenylate cyclase and decreased sensitivity to cAMP of cAMP-dependent protein kinase of the secretory mechanism of GH, in addition to the decrease in releasable GH pool and down regulation of GHRF receptors, may be involved in the desensitization mechanism.
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PMID:Desensitization of rat pituitary somatotrophs to growth hormone-releasing factor occurs in vitro. 289 86

This study aimed to investigate whether the growth hormone release and metabolic effects of ghrelin on AMPK activity of peripheral tissues are mediated by cannabinoid receptor type 1 (CB1) and the central nervous system. CB1-knockout (KO) and/or wild-type mice were injected peripherally or intracerebroventricularly with ghrelin and CB1 antagonist rimonabant to study tissue AMPK activity and gene expression (transcription factors SREBP1c, transmembrane protein FAS, enzyme PEPCK, and protein HSL). Growth hormone levels were studied both in vivo and in vitro. Peripherally administered ghrelin in liver, heart, and adipose tissue AMPK activity cannot be observed in CB1-KO or CB1 antagonist-treated mice. Intracerebroventricular ghrelin treatment can influence peripheral AMPK activity. This effect is abolished in CB1-KO mice and by intracerebroventricular rimonabant treatment, suggesting that central CB1 receptors also participate in the signaling pathway that mediates the effects of ghrelin on peripheral tissues. Interestingly, in vivo or in vitro growth hormone release is intact in response to ghrelin in CB1-KO animals. Our data suggest that the metabolic effects of ghrelin on AMPK in peripheral tissues are abolished by the lack of functional CB1 receptor via direct peripheral effect and partially through the central nervous system, thus supporting the existence of a possible ghrelin-cannabinoid-CB1-AMPK pathway.
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PMID:The CB1 receptor mediates the peripheral effects of ghrelin on AMPK activity but not on growth hormone release. 2398 45

Growth hormone (GH), in the recent past, has been recognized as a potent steroid stimulating hormone independent of gonadotropin (GtH). However, the mode and mechanism of its steroidogenic action in the testis is not yet elucidated, particularly in fish. The present study was designed to understand the mode and mechanism of steroidogenic action of growth hormone in testis of the catfish, Clarias batrachus through in vivo and in vitro Leydig cell culture studies using the signaling molecule inhibitors. Exogenous administration of GtH, GH and insulin to the male catfish increased testicular and circulating testosterone level. In vitro treatment of Leydig cells with these hormones also increased testosterone production. The steroidogenic action of GH appeared to be indirect and mediated through Leydig cell produced insulin-like growth factor I (IGF-I), as the treatments with actinomycin D, cycloheximide and anti-IGF-I abolished the GH-induced testosterone production by Leydig cells. The GH-induced stimulation in IGF-I production by the isolated Leydig cells further substantiates this notion. GH appears to employ cAMP/PKA and tyrosine kinase signaling pathways to induce IGF-I production, as the adenylyl cyclase inhibitor (SQ 22,536), cAMP-dependent protein kinase (PKA) blocker (H-89) and tyrosine kinase inhibitor (lavendustin A) abolished the GH-induced IGF-I production and in turn testosterone by the Leydig cells. This study suggests that GH exerts independent androgenic effect in the catfish testis indirectly through augmenting the Leydig cell production of IGF-I.
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PMID:Endocrine regulation of testosterone production by Leydig cells in the catfish, Clarias batrachus: probable mediators of growth hormone. 2565 Jan 68