Growth hormone regulates leptin gene expression in bovine adipose tissue: correlation with adipose IGF-1 expression.

Leptin, the product of the ob gene, is secreted from white adipocytes and regulates food intake and whole-body energy metabolism. In rodents and humans, leptin gene expression is under complex endocrine and metabolic control, and is strongly influenced by energy balance. Growth hormone (GH) has myriad effects on adipose tissue metabolism. The primary aim of this study was to determine the ability of GH to regulate leptin mRNA expression in bovine adipose tissue in vitro and in vivo. Incubation of subcutaneous adipose tissue explants for 24 h with GH alone had no effect on bovine leptin gene expression, whereas high concentrations of insulin or dexamethasone (DEX) potently stimulated bovine leptin mRNA abundance. GH, in combination with high concentrations of insulin, DEX, or both, attenuated the ability of insulin or DEX to stimulate leptin expression in vitro. These data indicate that GH can indirectly regulate leptin expression in vitro by altering the adipose tissue response to insulin or DEX. We extended these studies to examine the ability of GH to regulate leptin expression in vivo, using young castrate male cattle treated with no hormone (control) or GH (200 micrograms/kg body weight per day) for 3 days. GH increased plasma GH and insulin concentrations, but not those of cortisol or non-esterified fatty acid (NEFA) concentrations. GH treatment increased adipose tissue leptin and IGF-1 mRNA concentrations (n=9, P>0.001). In addition, leptin abundance was highly correlated with adipose tissue IGF-1 mRNA in GH-treated animals (P>0.001). The timing of GH-induced changes in leptin gene expression preceded measurable GH effects on adiposity.