Comparative Affinities of Adrenomedullin (AM) and Calcitonin Gene-Related Peptide (CGRP) for [125I] AM and [125I] CGRP Specific Binding Sites in Porcine Tissues |
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Abstract: | AbstractWe have investigated the binding characteristics of rat 125I] adrenomedullin (AM) and human 125I] calcitonin gene-related peptide (CGRP) to membranes prepared from a number of porcine tissues including atrium, ventricle, lung, spleen, liver, renal cortex and medulla. These membranes displayed specific, high affinity binding for 125I] rat AM and 125I] human CGRP. Porcine lung displayed the highest density of binding sites for radiolabeled AM and CGRP followed by porcine renal cortex. Competition experiments performed with 125I] rat AM indicated that the rank order of potencies of various peptides for inhibiting 125I] rat AM binding to various tissues were rat AM ≥ human AM ≥ human AM(22–52) > hαCGRP ≥ hαCGRP(8–37) <<<< sCT except spleen, atrium, renal cortex and renal medulla where rAM and hAM were 20–300 fold more potent than hAM(22–52). When the same experiments were performed using 125I] hαCGRP as the radioligand, the rank order potencies for various peptides were rAM = hAM > hαCGRP > hαCGRP(8–37) in most of the tissues except in spleen and liver. where hαCGRP was the most potent ligand. In lung, hαCGRP was almost as potent as rAM and hAM in displacing 125I] hαCGRP binding. These data suggest the existence of distinct CGRP and AM specific binding sites in contrast to previous reports that showed that both peptides interact differently in rat tissues. |
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