The Separate and Combined Effects of Insulin, Dexamethasone and Growth Hormone on the OB Gene Expression and Leptin Secretion from Cultured Human Visceral Adipose Tissue

ABSTRACT

PURPOSE: We investigated the hormonal control of OB gene expression and leptin secretion in cultured human visceral adipose tissue. METHODS: Visceral adipose tissues were cultured for up to 48 hrs in modified Eagle's medium with varying concentration of hormones Control(no hormone), bovine insulin(100 nM), Dexamethasone(DEX, 100 nM), growth hormone(GH, 40 ng/mL), insulin + DEX(100 nM each), insulin + DEX + GH(100 nM insulin and DEX, 40 ng/mL GH). Quantitative analysis of leptin mRNA was performed by competitive reverse transcription polymerase chain reaction, and leptin secretion in culture medium was measured by IRMA using a commercial kit. RESULTS: The addition of dexamethasone to the medium significantly increased OB gene expression and leptin secretion(P<0.05). Unlike dexamethasone, insulin did not affect OB gene expression and leptin secretion. Both insulin and dexamethasone, at high concentration, significantly stimulated leptin secretion compared with basal values(P<0.05). Leptin gene expression was not significantly increased by GH treatment alone, however GH, in combination with high concentrations of insulin and dexamethasone, attenuated the stimulatory effects of high concentrations of insulin and dexamethasone. CONCLUSION: Insulin cannot increase leptin secretion without the presence of dexamethasone. The mechanism suggested is that insulin may increase leptin secretion in cytoplasm only after dexamethasone increases the expression of OB gene. Further studies are necessary to elucidate the mechanism of the action of insulin on leptin secretion after increasing OB gene expression by dexamethasone.