Arginine increases growth hormone gene expression in rat pituitary and GH3 cells

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 microl 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 microl/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 (32)P-cDNA, and (32)P-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.