Porcine leptin alters isolated adipocyte glucose and fatty acid metabolism

Abstract

This study examined if leptin can acutely affect glucose or fatty acid metabolism in pig adipocytes and whether leptin’s actions on lipogenesis are manifested through interaction with insulin or growth hormone. Subcutaneous adipose tissue was obtained from ∼55 kg crossbred barrows at the USDA abattoir. Isolated adipocytes were prepared using a collagenase procedure. Experiments assessed U- 14 C -glucose or 1- 14 C -palmitate metabolism in isolated adipocytes exposed to: basal medium (control), 100 nM insulin, 100 ng/ml porcine growth hormone, 100 ng/ml recombinant porcine leptin, and combinations of these hormones. Treatments were performed in triplicate and the experiment was repeated with adipocytes isolated from five different animals. Cell aliquots (250 μl) were added to 1 ml of incubation medium, then incubated for 2 h at 37 °C for measurement of glucose and palmitate oxidation or incorporation into lipid. Incubation of isolated adipocytes with insulin increased glucose oxidation rate by 18% ( P<0.05), while neither growth hormone nor leptin affected glucose oxidation ( P>0.5). Total lipid synthesis from glucose was increased by approximately 25% by 100 nM insulin or insulin+growth hormone ( P<0.05). Insulin+leptin reduced the insulin response by 37% ( P<0.05). The combination of all three hormones increased total lipid synthesis by 35%, relative to controls ( P<0.05), a rate similar to insulin alone. Fatty acid synthesis was elevated by insulin (32%, P<0.05) or growth hormone (13%, P<0.05). Leptin had no effect on fatty acid synthesis ( P>0.05). Leptin reduced the esterification rate by 10% ( P<0.05). Growth hormone and insulin could overcome leptin’s inhibition of palmitate esterification ( P>0.05).