Insulin inhibits lipolytic activity and degradation of β-lipotropin in rabbit adipose tissue

β-Lipotropin, a pituitary peptide, is a potent stimulator of lipolysis in rabbit adipose tissue in vitro and in vivo. Insulin inhibited the β-lipotropin (1–100 nM)-stimulated glycerol release from rabbit adipocytes and fat pads significantly at concentrations of 10 and 100 μM. Both these concentrations of insulin also decreased the degradation of β-lipotropin in intact adipose tissue to the same extent as the lipolytic activity. Furthermore, insulin reduced the degradation of β-lipotropin in rabbit adipose tissue homogenate. Like insulin, several lysosomotropic agents also decreased significantly the degradation and the lipolytic activity of β-lipotropin. On the other hand, insulin-like growth factor I in lower concentrations (1–100 nM) did not effect degradation and lipolytic activity of β-lipotropin in rabbit adipose tissue. Thus, a direct influence of insulin on lysosomal enzymes degrading β-lipotropin in rabbit adipose tissue can be suggested.