Arginine Increases Growth Hormone Gene Expression in Rat Pituitary and GH3 Cells

Abstract

The effect of arginine (Arg) and Ornitargin^® (OT) [a compound containing the aminoacids Arg, citrulline (Cit) and ornithine (Orn)] administration upon growth hormone (GH) gene expression was studied both in vivo and in vitro (hemipituitaries and GH3 cells) by Northern blot analysis. For in vivo studies, adult male Wistar rats were anesthetized, subjected to i.v. infusion of 200 µl of 150 mM NaCl (control group), Arg (15 or 150 mg) or OT (15 mg of Arg, 1 mg of Cit and 4 mg of Orn) at a rate of 20 µl/min, and killed 50 min thereafter. For the in vitro studies, hemipituitaries or GH3 cells were incubated in 1 ml of appropriate medium containing Arg (15 or 150 mg) or OT (15 mg of Arg, 1 mg of Cit and 4 mg of Orn) for 60 min. The pituitaries of the in vivo and in vitro studies and GH3 cells were subsequently processed for RNA extraction. Total RNA was subjected to electrophoresis in agarose (1%)/formaldehyde gel, transferred to a nylon membrane and subjected to hybridization with a rat GH ³²P-cDNA, and ³²P-18S rRNA probe to correct for the variability in RNA loading. After autoradiography of the membrane, the abundance of GH mRNA and 18S rRNA bands was quantified by densitometry. The in vivo study demonstrated that Arg and OT infusion induced a 2.3-fold increase in GH mRNA expression, which could result from the Arg-mediated inhibition of somatostatin release. In addition, in vitro Arg, but not OT, induced GH gene expression in hemipituitaries and GH3 cells, indicating that the aminoacid can act per se at the pituitary somatotrope level. In conclusion, our data show for the first time that arginine stimulates GH gene expression in parallel to its recognized GH-releasing activity.

Potential Role of Growth Hormone in Impairment of Insulin Signaling in Skeletal Muscle, Adipose Tissue, and Liver of Rats Chronically Treated with Arginine

“…The data obtained show that Arg treatment increased GH mRNA expression, confirming our previous report (5,6), and also the pituitary GH content (6). One possible explanation for this finding might involve the well-known inhibitory effect of Arg upon somatostatin release (2, 7), which causes an increase in somatotropes' cAMP levels, and subsequently, activation of PKA and phosphorylation of pituitary transcriptional factors, like PIT 1, that causes marked alterations in GH gene transcription, as described (31).…”

“…We have previously demonstrated that acute (60 min, iv) and chronic (30 d) oral administration of Arg increases GH mRNA expression in rats, indicating that GH synthesis is being stimulated (5,6). However, although normoglycemic, rats treated chronically (30 d) with Arg presented hyperinsulinemia and reduced blood glu-cose decay rate after an insulin challenge, which indicates the occurrence of insulin resistance (6).…”

Stimulatory Effect of Interleukin-1β on Growth Hormone Gene Expression and Growth Hormone Release from Rat GH3 Cells

“…GH3 cells, a rat pituitary tumor cell line that secretes both GH and prolactin (PRL), was purchased from American Type Culture Collection (Manassas, Va., USA) and used for the study on GH release and regulation of expression [21, 22]. GH3 cells were maintained in Dulbecco’s modified Eagle’s Medium (Life Technologies, Grand Island, N.Y., USA) supplemented with 20% fetal bovine serum and antibiotics (100 U/ml penicillin and 100 U/ml streptomycin) in a 5% CO 2 -95% air atmosphere at 37°C.…”

The regulatory mechanism by which interleukin-6 stimulates GH-gene expression in rat GH3 cells

“…These cells have been used previously by ourselves and others as an accepted model for studying both GH-gene expression and the molecular mechanism involved (Tamura et al 2000, Gong et al 2003a, 2003b, Adriao et al 2004.…”