Pittman R N, Reynolds E E, Molinoff P B
J Pharmacol Exp Ther. 1984 Sep;230(3):614-8.
The intrinsic activities of 14 agonists at beta adrenergic receptors were determined in membranes prepared from control L6 muscle cells or from cells preincubated in the presence of isoproterenol for 20 min. Several drugs that were full agonists when studied with membranes from naive cells were partial agonists in membranes prepared from desensitized cells. Prolonged incubation of cells with agonists resulted in a 70 to 80% decrease in the density of beta adrenergic receptors. This effect was observed after incubation of cells with either full or partial agonists, suggesting that the extent of receptor loss is independent of the intrinsic activity of an agonist. The rate of receptor loss was related, however, to the intrinsic activity of an agonist. The rate of receptor loss correlated with the intrinsic activities of agonists in desensitized (r = 0.94) and control (r = 0.87) membranes.
在从对照L6肌肉细胞或在异丙肾上腺素存在下预孵育20分钟的细胞制备的膜中，测定了14种β肾上腺素能受体激动剂的内在活性。在用未致敏细胞的膜进行研究时为完全激动剂的几种药物，在脱敏细胞制备的膜中为部分激动剂。用激动剂长时间孵育细胞导致β肾上腺素能受体密度降低70%至80%。在用完全或部分激动剂孵育细胞后均观察到这种效应，这表明受体丧失的程度与激动剂的内在活性无关。然而，受体丧失的速率与激动剂的内在活性有关。受体丧失的速率与脱敏膜（r = 0.94）和对照膜（r = 0.87）中激动剂的内在活性相关。
