Effect of cell size on lipolysis and antilipolytic action of insulin in human fat cells

The lipolytic response to catecholamines and the antilipolytic effect of insulin were studied as a function of adipose cell size and number. The results show that cellular enlargement is associated with an increase in the basal lipolysis as well as the release of glycerol induced by salbutamol (a β2-receptor agonist), noradrenaline, adrenaline, and isopropylnoradrenaline. The glycerol release induced by all these agents seems to be more favorably correlated with cell surface area than with cell volume or diameter.Under the incubation conditions used with glucose in the medium, the antilipolytic effect of insulin on the basal as well as on the adrenaline- and isopropylnoradrenaline-stimulated lipolysis was not consistent at any cell size studied. However, in the presence of noradrenaline and salbutamol, insulin exerted a consistent antilipolytic effect. The results show that the larger adipose cells are at least as sensitive to the antilipolytic effect of insulin as the smaller cells.The results imply that the previously reported diminished responsiveness to insulin shown by large adipose cells is exerted only on the side of lipid accumulation. It is suggested that the negative correlation between cell size and responsiveness to insulin on the side of lipid accumulation may be one way to control adipose cell enlargement.