Vol. 304, Issue 1, 326-333, January 2003

Investigation of CGRP Receptors and Peptide Pharmacology in Human Coronary Arteries. Characterization with a Nonpeptide Antagonist

Philip Hasbak , Ole Saetrum Opgaard, Karen Eskesen, Søren Schifter, Henrik Arendrup, Jenny Longmore and Lars Edvinsson

Department of Clinical Experimental Research (P.H., K.E., L.E.), Department of Clinical Physiology and Nuclear Medicine (P.H., S.S.), University Hospital of Copenhagen, Glostrup, Denmark; Department of Medicine (O.S.O.), Kaiser Permanente Medical Center, San Francisco, California; Department of Thoracic Surgery (H.A.), Rigshospitalet, Copenhagen, Denmark; and Merck Sharp and Dohme, Neuroscience Research Centre (J.L.), Harlow, Essex, United Kingdom

Calcitonin gene-related peptide (CGRP), adrenomedullin (AM), and amylin are structurally related peptides mediating vasorelaxation in the coronary circulation possibly via CGRP receptors (subtypes 1 or 2). Functional CGRP₁ receptors appear to consist of at least three different kinds of proteins: the calcitonin receptor-like receptor (CRLR), receptor-activity-modifying proteins (RAMPs) and the receptor component protein (RCP). No CGRP₂ receptor has yet been cloned. Using reverse transcriptase - polymerase chain reaction, the presence of mRNA sequences encoding CRLR, RCP and RAMPs was demonstrated in human coronary arteries. Relaxant responses were studied on isolated segments of coronary arteries after precontraction with U46619 (9,11-dideoxy-11,9-epoxymethano-prostaglandin F₂). The human peptides CGRP, AM, and amylin induced relaxation with mean pEC₅₀ values of 8.6, 6.8, and 6.3 M, respectively. Preincubation with CGRP_8-37 (10⁷ -10⁵ M) and a novel nonpeptide CGRP antagonist "Compound 1" (WO98/11128) (10⁷-10⁵ M) caused a dose-dependent rightward shift of the concentration-response curves for CGRP with pA₂ values of 7.0 and 7.1, respectively. Preincubation with CGRP_8-37 (10⁶ M) and Compound 1 (10⁶ M) caused significant rightward shift of the concentration-response curves for AM and amylin as well with pK_B values between 6.6 and 7.5. Preincubation with AM_22-52 had no antagonistic effect on the AM and amylin response, neither did diacetoamidomethyl cysteine CGRP cause any concentration dependent (10¹¹-10⁶ M) dilatation. In conclusion, mRNA for the components forming CGRP₁ and AM receptors was detected in the human left anterior descending coronary arteries. CGRP, AM, and amylin mediated vasorelaxation via the CGRP₁ receptor. Compound 1 acted as a nonpeptide antagonist at the CGRP₁ receptor and could thus become a tool for the study of CGRP-mediated functional responses in human tissue.