Acquisition of increased hormone sensitivity during in vitro adipocyte development

Murine 3T3 L1 fibroblasts enter a differentiation program subsequent to prolonged maintenance in the confluent state and develop into adipocytes. The hormone sensitivity of adenylate cyclase and the physiological responsiveness to insulin were compared in 3T3 L1 preadipocytes and adipocytes. The following observations, comprising several distinct categories of hormone responsiveness, were made. (2.5 μM) isoproterenol stimulated adenylate cyclase 15 fold in adipocyte homogenates, but only 2.5 fold in preadipocyte preparations, suggesting a considerable magnification in β adrenergic responsiveness during development. A totally new control element, adrenocorticotropic hormone responsiveness, was incorporated into the adenylate cyclase system of the adipocytes. Sensitivity to prostaglandin E₁ was observed in both preadipocytes and adipocytes, but no change in responsiveness could be detected in the differentiated cells. Glucagon sensitive adenylate cyclase could not be detected in either preadipocytes or adipocytes. Both preadipocytes and adipocytes possess considerable insulin binding activity, but near physiological levels of insulin stimulate the conversion of glucose to CO₂ and lipid only in the differentiated cells.