ADIPSIN EXPRESSION AND GROWTH IN RATS AS INFLUENCED BY INSULIN AND SOMATOTROPIN

Adipsin is a molecular marker of obesity in rodents. Content of adipsi n protein in blood and mRNA in adipocytes is significantly reduced in several genetic and experimentally induced obese models. It has been s uggested that this reduction in adipsin is causative to obesity develo pment. Insulin reduces adipsin expression in vitro and is negatively c orrelated with adipsin expression in vivo. Because bovine somatotropin (bST) opposes many actions of insulin and can reduce body fat content , we tested the hypothesis that bST enhances adipsin expression. In tw o experiments using 210 rats, bST and a similar hormone, bovine placen tal lactogen (bPL), both caused a small (14 to 27%) but statistically significant reduction in circulating adipsin protein. Because exogenou s bST can increase circulating insulin we next used a diabetic model t o test the bST effect on adipsin. In rats treated with streptozotocin and injected daily with insulin (STZ+I), bST had no effect on circulat ing adipsin. Additional variables related to growth were influenced di fferently by bST in normal vs. STZ+I animals. In conclusion, the drop in circulating adipsin following bST administration in normal rats is dependent upon the animals' ability to secrete insulin.