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  • Endogenous somatostatin is critical in regulating the acute effects of L-arginine on growth hormone and insulin release in mice.

Endogenous somatostatin is critical in regulating the acute effects of L-arginine on growth hormone and insulin release in mice.

Endocrinology (2013-05-23)
Jose Córdoba-Chacón, Manuel D Gahete, Ana I Pozo-Salas, Justo P Castaño, Rhonda D Kineman, Raul M Luque
ABSTRACT

l-arginine (l-Arg) rapidly stimulates GH and insulin release in vivo. It has been hypothesized that l-Arg stimulates GH release by lowering hypothalamic somatostatin (SST) tone. l-Arg may also act directly at the pituitary to stimulate GH release. Moreover, l-Arg has a direct stimulatory effect on β-cells, which is thought to be blunted by the release of SST from pancreatic δ-cells. To confirm the role of endogenous SST on l-Arg-induced GH and insulin release, wild-type (WT) and SST-knockout (SST-KO) mice were injected with l-Arg (ip; 0.8 g/kg), and pre-/post-injection GH, insulin, and glucose levels were measured. In WT mice, l-Arg evoked a 6-fold increase in circulating GH. However, there was only a modest increase in GH levels in WT pituitary cell cultures treated with l-Arg. In contrast, l-Arg failed to increase GH in SST-KO beyond their already elevated levels. These results further support the hypothesis that the primary mechanism by which l-Arg acutely increases GH in vivo is by lowering hypothalamic SST input to the pituitary and not via direct pituitary effects. Additionally, l-Arg induced a clear first-phase insulin secretion in WT mice, but not in SST-KO. However, SST-KO, but not WT mice, displayed a robust and sustained second-phase insulin release. These results further support a role for endogenous SST in regulating l-Arg-mediated insulin release.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Somatotropin (STH) from porcine pituitary
SAFC
L-Arginine
Sigma-Aldrich
L-Arginine, reagent grade, ≥98%
Sigma-Aldrich
L-Arginine, from non-animal source, meets EP, USP testing specifications, suitable for cell culture, 98.5-101.0%
Sigma-Aldrich
L-Arginine, 99%, FCC, FG
Sigma-Aldrich
L-Arginine, BioUltra, ≥99.5% (NT)
Supelco
L-Arginine, Pharmaceutical Secondary Standard; Certified Reference Material