Growth hormone-releasing hormone is produced by adipocytes and regulates lipolysis through growth hormone receptor

BACKGROUND: Growth hormone-releasing hormone (GHRH) has a crucial role in growth hormone (GH) secretion, but little is known about its production by adipocytes and its involvement in adipocyte metabolism. OBJECTIVES: To determine whether GHRH and its receptor (GHRH-R) are present in human adipocytes and to study their levels in obesity. Also, to analyze the effects of GHRH on human adipocyte differentiation and lipolysis. METHODS: GHRH/GHRH-R and GH/GH-R mRNA expression levels were analyzed in human mature adipocytes from non-obese and morbidly obese subjects. Human mesenchymal stem cells (HMSC) were differentiated to adipocytes with GHRH (10(-14)-10(-8) M). Adipocyte differentiation, lipolysis and gene expression were measured and the effect of GH-R silencing was determined. RESULTS: Mature adipocytes from morbidly obese subjects showed a higher expression of GHRH and GH-R, and a lower expression of GHRH-R and GH than non-obese subjects (P < 0.05). A total of 10(-14)-10(-10) M GHRH induced an inhibition of lipid accumulation and PPAR-gamma expression (P < 0.05), and an increase in glycerol release and HSL expression (P<0.05) in human differentiated adipocytes. A total of 10(-12)-10(-8) M GHRH decreased GHRH-R expression in human differentiated adipocytes (P<0.05). A total of 10(-10)-10(-8) M GHRH increased GH and GH-R expression in human differentiated adipocytes (P<0.05). The effects of GHRH at 10(-10) M on adipocyte differentiation and lipolysis were blocked when GH-R expression was silenced. CONCLUSIONS: GHRH and GHRH-R are expressed in human adipocytes and are negatively associated. GHRH at low doses may exert an anti-obesity effect by inhibiting HMSC differentiation in adipocytes and by increasing adipocyte lipolysis in an autocrine or paracrine pathway. These effects are mediated by GH and GH-R.