Pessin J E, Gitomer W, Oka Y, Oppenheimer C L, Czech M P
J Biol Chem. 1983 Jun 25;258(12):7386-94.
Incubation of intact rat adipocytes with physiological concentrations of catecholamines inhibits the specific binding of 125I-insulin and 125I-epidermal growth factor (EGF) by 40 to 70%. Affinity labeling of the alpha subunit of the insulin receptor demonstrates that the inhibition of hormone binding is directly reflective of a specific decrease in the degree of receptor occupancy. The stereospecificity and dose dependency of the binding inhibitions are typical of a classic beta 1-adrenergic receptor response with half-maximal inhibition occurring at 10 nM R-(-)-isoproterenol. Specific alpha-adrenergic receptor agonists and beta-adrenergic receptor antagonists have no effect, while beta-adrenergic receptor antagonists block the inhibition of 125I-insulin and 125I-EGF binding to receptors induced by beta-adrenergic receptor agonists. Further, these effects are mimicked by incubation of adipocytes with dibutyryl cyclic AMP or with 3-isobutyl-1-methylxanthine. The beta-adrenergic inhibition of both 125I-insulin and 125I-EGF binding is very rapid, requiring only 10 min of isoproterenol pretreatment at 37 degrees C for a maximal effect. Removal of isoproterenol by washing the cells in the presence of alprenolol leads to complete reversal of these effects. The inhibition of 125I-EGF binding is temperature dependent whereas the inhibition of 125I-insulin binding is relatively insensitive to the temperature of isoproterenol pretreatment. Scatchard analysis of 125I-insulin and 125I-EGF binding demonstrated that the decrease of insulin receptor-binding activity may be due to a decrease in the apparent number of insulin receptors while the inhibition of EGF receptor binding can be accounted for by a decrease in apparent EGF receptor affinity. The decrease in the insulin receptor-binding activity is physiologically expressed as a dose-dependent decrease of insulin responsiveness in the adipocyte with respect to two known responses, stimulation of insulin-like growth factor II receptor binding and activation of the glucose-transport system. These results demonstrate a beta-adrenergic receptor-mediated cyclic AMP-dependent mechanism for the regulation of insulin and EGF receptors in the rat adipocyte.
用生理浓度的儿茶酚胺孵育完整的大鼠脂肪细胞，可使125I胰岛素和125I表皮生长因子（EGF）的特异性结合抑制40%至70%。胰岛素受体α亚基的亲和标记表明，激素结合的抑制直接反映了受体占据程度的特异性降低。结合抑制的立体特异性和剂量依赖性是典型的经典β1 - 肾上腺素能受体反应，在10 nM R - (-) - 异丙肾上腺素时出现半数最大抑制。特异性α - 肾上腺素能受体激动剂和β - 肾上腺素能受体拮抗剂无作用，而β - 肾上腺素能受体拮抗剂可阻断β - 肾上腺素能受体激动剂诱导的125I胰岛素和125I EGF与受体结合的抑制。此外，用二丁酰环磷酸腺苷或3 - 异丁基 - 1 - 甲基黄嘌呤孵育脂肪细胞可模拟这些效应。β - 肾上腺素能对125I胰岛素和125I EGF结合的抑制非常迅速，在37℃下仅需10分钟的异丙肾上腺素预处理即可产生最大效应。在阿普洛尔存在下洗涤细胞以去除异丙肾上腺素可导致这些效应完全逆转。125I EGF结合的抑制是温度依赖性的，而125I胰岛素结合的抑制对异丙肾上腺素预处理温度相对不敏感。对125I胰岛素和125I EGF结合的Scatchard分析表明，胰岛素受体结合活性的降低可能是由于胰岛素受体表观数量的减少，而EGF受体结合的抑制可归因于EGF受体表观亲和力的降低。胰岛素受体结合活性的降低在生理上表现为脂肪细胞中胰岛素反应性相对于两种已知反应（胰岛素样生长因子II受体结合的刺激和葡萄糖转运系统的激活）的剂量依赖性降低。这些结果证明了一种β - 肾上腺素能受体介导的环磷酸腺苷依赖性机制，用于调节大鼠脂肪细胞中的胰岛素和EGF受体。
