Characterization of beta-adrenergic receptors in fish and amphibian lymphoid organs

Cells from goldfish and amphibian lymphoid organs, mainly leukocytes, expre ss high affinity beta-adrenergic receptors specific for beta-adrenergic lig ands (agonists: adrenaline, noradrenaline, terbutaline, and fenoterol; anta gonists: CGP-12177, dihydroalprenolol, propranolol, atenolol, and butoxamin e). The rank order of ligand potency does not allow their being classified into any known mammalian subtype, Among features that distinguish them from mammalian beta(1) and beta(2)-adrenoceptors is much lower affinity for (-) -CGP-12177, obtained in both saturation and kinetic experiments (about 25 n M for goldfish head kidney cells). The density of receptors on goldfish and anuran cells is organ-dependent and comparable to that estimated on mammal ian leukocytes. The extraordinarily high receptor density on salamander spl enic cells (about 183,000) correlates with the large size of urodele cells. The competition experiments on goldfish cells with propranolol and CGP-121 77 suggest the existence of yet another binding site, which may be either a nother beta-AR subtype, or a serotonergic receptor. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.