Insensitivity of large rat adipocytes to the antilipolytic effects of insulin.

The ability of insulin to inhibit epinephrine-stimulated lipolysis was compared in large and small rat adipocytes. Large cells were obtained from older, obese animals (greater than 12 months old and greater than 500 g) and small cells were obtained from younger, leaner animals (4-5 weeks ild, 140-160 g). When full insulin dose response studies were conducted it was found that large adipocytes were less sensitive to the antilipolytic effects of insulin. Thus, decreased insulin responses were seen at low insulin concentrations, while normal inhibition of lipolysis was seen at a maximally effective insulin concentration. In other words, the dose response curve for insulin's antilipolytic action was shifted to the right, and this is consistent with the previously reported decrease of insulin receptors in these cells. Furthermore, since the maximal antilipolytic response to insulin was fully normal in large adipocytes, the data also indicate that the post receptor antilipolytic system is intact in these cells.