Influence of cell size on the effects of insulin and noradrenaline on human adipose tissue.

In the present study dose-response relationships of the effects of noradrenaline and insulin on fat cells of different sizes were performed. Adipose cells larger than 100 mum were more responsive (expressed as absolute effects) to the lipolytic action of noradrenaline as well as to the antilipolytic effect of insulin. This suggests that in the larger cells the capacity, i.e. the sum of factors contributing to the ability to stimulate or inhibit the metabolic rates, was greater than in the smaller ones. In contrast the sensitivity to these agents, i.e. the readiness to respond, was not different between small and large cells. It is shown that the concentrations of insulin needed to obtain an antilipolytic effect is far below that needed to stimulate glucose incorporation. This discrepancy in insulin concentrations required may be due to binding of insulin to receptors with different affinity.