Search

1. This study describes the effects of hypoxia on relaxing responses and cAMP production induced by the known vasodilator peptides: alphaCGRP, amylin (AMY) and adrenomedullin (AM) on isolated pig coronary arteries in vitro. 2. Hypoxic incubation increased the vasorelaxant effect of alphaCGRP (four-fold; P

Calcitonin gene-related peptide (CGRP), amylin and adrenomedullin (AM) belong to the same family of peptides. Accumulating evidence indicate that the calcitonin (CT) receptor, the CT receptor-like receptor (CRLR) and receptor-activity-modifying proteins (RAMPs) form the basis of all the receptors in this family of peptides. Using reverse transcriptase–polymerase chain reaction the presence of mRNA sequences encoding the CRLR, RAMP1 and RAMP2 were demonstrated in porcine left anterior descending (LAD) coronary arteries, whereas porcine calcitonin (CT) receptor mRNA was not present. The partial porcine mRNA sequences shared 82–92% nucleotide identity with human sequences. The human peptides αCGRP, βCGRP, AM and amylin induced relaxation with pEC50 values of 8.1, 8.1, 6.7 and 6.1 M respectively. The antagonistic properties of a novel non-peptide CGRP antagonist ‘Compound 1’ (WO98/11128), βCGRP8–37 and the proposed AM receptor antagonist AM22–52 were compared to the well-known CGRP1 receptor antagonist αCGRP8–37. The αCGRP8–37 and βCGRP8–37 induced concentration-dependent (10−7–10−5 M) rightward shift of both the αCGRP and βCGRP concentration-response curves. βCGRP8–37 (10−6 M) had the same effect as αCGRP8–37 (10−6 M), but with less potent rightward shift of the concentration-response curves for αCGRP, AM and amylin. Preincubation with ‘Compound 1’ (10−7–10−5 M) and AM22–52 (10−6 M) had no significant antagonistic effect. In conclusion, the building blocks forming CGRP and AM receptors were present in the porcine LAD, whereas those of the amylin receptor were not. αCGRP, βCGRP, AM and amylin mediated vasorelaxation via the CGRP receptors. No functional response was detected to adrenomedullin via the adrenomedullin receptor. British Journal of Pharmacology (2001) 133, 1405–1413; doi:10.1038/sj.bjp.0704210

1. This study describes the effects of hypoxia on relaxing responses and cAMP production induced by the known vasodilator peptides: alphaCGRP, amylin (AMY) and adrenomedullin (AM) on isolated pig coronary arteries in vitro. 2. Hypoxic incubation increased the vasorelaxant effect of alphaCGRP (four-fold; P0.05), AMY (3.2-fold; P0.05), but not significantly for AM (two-fold; NS). 3. Whereas hypoxia had no effect on arterial cAMP levels, it significantly potentiated the production of cAMP stimulated of alphaCGRP and AMY, but not of AM. 4. The antagonist alphaCGRP(8-37) also exerted an increased effect in hypoxia. The Schild plot-derived pK(B) values revealed an increase in the apparent affinity of the antagonist for the CGRP(1) receptor from 7.0 to 7.2 under control conditions versus 8.0 in hypoxia. 5. Removal of endothelium, peptidase inhibitors, preincubation with the adenosine A(2A) receptor antagonist CSC (10(-3) M), the ATP-sensitive K-channel inhibitor glibenclamide (10(-5) M), the cyclooxygenase inhibitor indomethacin (10(-3) M) or NG-monomethyl-L-arginine (10(-4) M) had no effect on the alphaCGRP-induced vasorelaxation in hypoxia; neither did hypoxia influence the levels of CGRP and AM receptor mRNA. 6. We conclude that hypoxic incubation increases the relaxation and cAMP production induced by alphaCGRP and AMY in rings of porcine coronary arteries in vitro. A concomitant release of adenosine, a cyclooxygenase product, an endothelium-derived substance, activation of vascular ATP-sensitive K-channels, peptidase inhibitors or changes in CGRP and AM receptor mRNA cannot account for the changes observed in hypoxia. Moreover, alphaCGRP(8-37) showed increased affinity at the CGRP(1) receptor during hypoxia, possibly due to a conformational change at the CGRP(1) receptor site.