Effect of Serum, α-1 Acid Glycoprotein, Lipoproteins and Albumin on Human Mononuclear Leucocyte β-Adrenoceptors

Abstract

The effects of serum, .alpha.-1 acid glycoprotein (AAG), serum lipoproteins (SLP) and human serum albumin (HSA) on 3H-(-)-dihydroalprenolol (3H-(-)-DHA) binding and (-)-isoproterenol ((-)-IPR) induced cyclic AMP (cAMP) elevation in human peripheral blood mononuclear leucocytes (MNL) were investigated. The saturable binding of 3H-(-)-DHA was decomposed into two classes of binding sites with maximum binding capacity of approximately 1400 and 30,000 sites/cell and with dissociation constants (Kd) of approximately 0.7 and 65 nM. Stimulation of the MNL .beta.-adrenoceptors by (-)-IPR caused a concentration dependent cAMP accumulation (EC50 .apprx. 0.2 .mu.M) with maximum level approximately 250% above basal. For all single leucocyte preparations, 30-35 min. exposure to serum, AAG and SLP increased the number of .beta.-adrenoceptors with 100-200% and the maximal responsiveness to (-)-IPR with 30-90%. The presence of proteins did not change the Kd or the EC50. (-)-Alprenolol inhibited concentration dependently the serum induced increment in (-)-IPR-responsiveness. Serum, AAG and SLP did also increase the number of low affinity binding sites with 25-40% without effect on the Kd. HSA had no consistent effect on .beta.-adrenergic binding or stimulation. The present study shows that serum, AAG and SLP influence the number and function of MNL .beta.-adrenoceptors in vitro.