Biphasic insulin modulation of β 2-adrenoceptors in man

Abstract

The plasticizers tris-(2-butoxyethyl)-phosphate (TBEP) and di-(2-ethylhexyl)-phthalate (DEHP) and the β-adrenergic receptor-blockers [3H]-(−)-dihydroalprenolol ([3H]-(−)-DHA) and [3H]-(−)-CGP 12177 were tested for their ability to interact with β-adrenergic binding to α1-acid glycoprotein (AAG) and mononuclear leukocytes (MNL). The ic50-values, obtained by displacement of [3h]-(−)-DHA bound to AAG, were 3.5 nM, 2 μM and 4 μM for TBEP, (-)-alprenolol and DEHP, respectively. (±)-CGP 12177 had virtually no effect on radioligand binding to AAG. The[3H]-(−)-CGP 12177 binding to MNL consisted of β-adrenergic receptor binding (Kd = 210 pM) and non-saturable binding. [3H]-(−)-DHA was bound to two different classes of binding sites on MNL, the β-adrenergic receptors (Kd = 440 pM) and a secondary class of binding sites (Kd = 64 nM). (±)-CGP 12177 displaced about 30% of [3H]-(−)-DHA from MNL with an ic50-value of 190 pm. (−)-ALP displaced about 85% of total bound radioligand and gave a biphasic displacement curve with ic50-values of 320 pM and 690 mM, respectively. TBEP displaced a considerable fraction of [3H]-(-)CGP 12177 and [3H]-(−)DHA bound to MNL β-adrenergic receptors, whereas DEHP had no effect. In contrast, DEHP caused displacement of [3h]-(−)-dha from the MNL low affinity sites, but was a markedly less potent displacer compared to TBEP. The present study shows that TBEP and DEHP interact with β-adrenergic transport proteins, non-specific tissue binding sites and β-adrenergic receptors coupled to adenylate cyclase. Plasticizers may thus affect the biology and pharmacology of the β-adrenergic signal system.