Effects of body weight restriction on blood and adipose tissue adipokines and macrophage activation in obese and insulin-resistant ponies

Abstract

The aim of the present study was to investigate the changes in selected blood adipokines and subcutaneous adipose tissue adipokine and macrophage activation marker (CD68) mRNA expression profiles in overweight or obese insulin-resistant (IR) ponies during a body weight reduction programme. It was hypothesized that insulin effectiveness (insulin sensitivity or resistance) was accompanied by differences in circulating blood adipokines and different subcutaneous adipose adipokine mRNA expression profiles before and after weight reduction. Fifteen obese ponies were used in a body weight (BW) reduction programme (BWRP, daily energy intake: 7.0-8.4 MJ/100 kg BW). A frequently sampled intravenous glucose tolerance test was used to assess insulin sensitivity. Subcutaneous adipose tissue biopsies of the tail head were obtained for mRNA expression profiles of adiponectin, retinol binding protein 4 (RBP4), interleukin 6 (IL-6) and macrophage activation marker (CD68) before and after BWRP. Blood samples were analyzed for serum leptin, serum RBP4 and plasma adiponectin. Significant BW losses occurred with 7 MJ DE/100 kg BW. Serum leptin and RBP4 were initially similar between insulin-resistant (IR) and insulin-sensitive (IS) ponies, and both significantly decreased during BWRP. Compared with IS ponies, IR ponies initially had significantly lower plasma adiponectin levels. RNA expression of RBP4, adiponectin, IL-6 and CD 68 was similar between IR and IS ponies. Plasma adiponectin appears strongly related to IR, whereas serum leptin and RBP4 are closely linked to adiposity, independent of insulin sensitivity. Adipose tissue mRNA expression profiles did not clearly reflect these differences. However, the role of subcutaneous adipose tissue in IR remains open.