Detection of beta-adrenergic receptors on rabbit mononuclear cells isolated free of significant contamination by other cell types

Determination of beta adrenoceptor density on rabbit mononuclear leukocytes

The purpose of the present study was to devise a technique for the isolation of a relatively homogeneous mononuclear leukocyte (MNL) preparation from rabbit whole blood and determine the density and affinity of beta-adrenoceptors on MNL. A modified method based upon that by Böyum was developed to maximize isolation of MNL from red blood cells (RBC), granulocytes, and platelets. The method involved an initial centrifugation to remove platelets and two centrifugations with a Ficoll solution to eliminate RBC and granulocytes. beta-Adrenoceptor density as determined with [125I]cyanopindolol and MNL membrane or whole cell preparations ranged between 317 and 360 sites per cell. Affinity for the binding sites was dependent upon whether membrane or whole cell preparations were studied, being 56.3 +/- 9.9 and 11.4 +/- 1.4 pM, respectively. Binding sites were found to be saturable and noncooperative. In addition, the binding sites demonstrated selectivity and stereospecificity for beta-adrenoceptor ligands. It is concluded that the modified method of harvesting MNL from rabbit whole blood provides a relatively homogeneous cell suspension that can be used to study the beta-adrenoceptor system.

Stress induced desensitization of lymphocyte beta-adrenoceptors in young and aged rats

The effects of different times of immobilization stress on intact lymphocyte beta-adrenoceptors and plasma corticosterone were compared in 3-month and 24-month-old rats. In young animals after 30 min restraint 3H-dihydroalprenolol specific binding was significantly reduced (61% of control value) and plasma corticosterone significantly raised (186% of control). The effect on beta-adrenoceptors was due changes in receptor number (Bmax) without any effect on affinity (KD). In aged rats both effects were only seen after 180 min restraint and were less pronounced. Isoproterenol treatment in vitro reduced beta-adrenoceptors on lymphocytes. This effect was less pronounced in lymphocytes from aged rats. Corticosterone in vitro increased 3H-dihydroalprenolol specific binding. We therefore suggest that the decrease of beta-adrenoceptors reflects an adaptive response to the stress-induced catecholamine release and that corticosterone could play a role in reversing this effect. This adaptive response to stress seems to be impaired in aged animals.

Characterization of histamine H-1 receptors on human peripheral lung

Histamine H-1 receptors in human peripheral lung were characterized by radioligand and biochemical assays employing binding of the H-1 receptor antagonist [3H]pyrilamine to plasma membrane preparations. Simultaneous computerized analyses of the data from fourteen separate equilibrium-binding assays indicated the presence of three distinct classes of binding sites with Kd values of 81 +/- 35 pM, 7 +/- 3 microM, and 320 +/- 167 microM and binding capacities of 23 +/- 3 pmoles, 10 +/- 5 nmoles, and 297 +/- 119 nmoles/mg protein respectively. Dissociation kinetics of [3H]pyrilamine binding also supported the presence of three binding sites or states. Further, competition binding curves for histamine receptor agonists and antagonists also indicated the presence of multiple binding sites for the H-1 receptor. The effect of exogenous stimulation of histamine H-1 receptors on human cyclic nucleotides was also examined. Both histamine and the H-1 agonist 2-methyl histamine caused dose-related increases in the cyclic guanosine monophosphate (GMP) content of human lung. The effects of 2-methyl histamine were selective for cyclic GMP. The histamine-induced increase in cyclic GMP peaked within 1.0 min and was effectively prevented by the H-1 antagonist pyrilamine. Thus, human lung possesses a large number of H-1 receptors which exhibit three binding states and produce cyclic GMP, but not cyclic adenosine monophosphate (AMP), when stimulated.