Suppression of the nocturnal rise in growth hormone reduces subsequent lipolysis in subcutaneous adipose tissue

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Abstract
The aim of this study was to examine the effect of the nocturnal rise in growth hormone (GH) concentration on lipolysis in adipose tissue the following morning. Eight healthy subjects were studied on two occasions (control vs. suppression of GH secretion) and six were studied on a third occasion (control vs. replacement of GH). Lipolysis in the whole body was assessed by measurement of systemic glycerol turnover. Lipid metabolism in the subcutaneous adipose tissue of the anterior abdominal wall was studied by measurement of arterio-venous differences. Suppression of the nocturnal rise in GH did not affect systemic glycerol turnover. However, in subcutaneous abdominal adipose tissue it led to a significant reduction in the veno-arterial differences in nonesterified fatty acid (NEFA, P = 0.041) and glycerol (P = 0.014) concentrations, reflecting a reduction in intracellular lipolysis (P = 0.011). Although arterialized plasma triacylglycerol (TG) concentrations were reduced in the absence of the nocturnal GH pulse, the extraction of TG in subcutaneous abdominal adipose tissue remained unchanged. We conclude that the normal nocturnal rise in plasma GH concentration leads to site-specific regulation of lipolysis in adipose tissue on the following day, with preferential fat mobilization from central depots.