Article date: July 2005
By: Philip Hasbak, Karen Eskesen, Søren Schifter, Lars Edvinsson in Volume 145, Issue 5, pages 646-655
This study describes the effects of hypoxia on relaxing responses and cAMP production induced by the known vasodilator peptides: αCGRP, amylin (AMY) and adrenomedullin (AM) on isolated pig coronary arteries in vitro.
Hypoxic incubation increased the vasorelaxant effect of αCGRP (four‐fold; P<0.05), AMY (3.2‐fold; P<0.05), but not significantly for AM (two‐fold; NS).
Whereas hypoxia had no effect on arterial cAMP levels, it significantly potentiated the production of cAMP stimulated of αCGRP and AMY, but not of AM.
The antagonist αCGRP8–37 also exerted an increased effect in hypoxia. The Schild plot‐derived pKB values revealed an increase in the apparent affinity of the antagonist for the CGRP1 receptor from 7.0 to 7.2 under control conditions versus 8.0 in hypoxia.
Removal of endothelium, peptidase inhibitors, preincubation with the adenosine A2A 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 αCGRP‐induced vasorelaxation in hypoxia; neither did hypoxia influence the levels of CGRP and AM receptor mRNA.
We conclude that hypoxic incubation increases the relaxation and cAMP production induced by αCGRP 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, αCGRP8–37 showed increased affinity at the CGRP1 receptor during hypoxia, possibly due to a conformational change at the CGRP1 receptor site.
This study describes the effects of hypoxia on relaxing responses and cAMP production induced by the known vasodilator peptides: αCGRP, amylin (AMY) and adrenomedullin (AM) on isolated pig coronary arteries in vitro.
Hypoxic incubation increased the vasorelaxant effect of αCGRP (four‐fold; P<0.05), AMY (3.2‐fold; P<0.05), but not significantly for AM (two‐fold; NS).
Whereas hypoxia had no effect on arterial cAMP levels, it significantly potentiated the production of cAMP stimulated of αCGRP and AMY, but not of AM.
The antagonist αCGRP8–37 also exerted an increased effect in hypoxia. The Schild plot‐derived pKB values revealed an increase in the apparent affinity of the antagonist for the CGRP1 receptor from 7.0 to 7.2 under control conditions versus 8.0 in hypoxia.
Removal of endothelium, peptidase inhibitors, preincubation with the adenosine A2A 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 αCGRP‐induced vasorelaxation in hypoxia; neither did hypoxia influence the levels of CGRP and AM receptor mRNA.
We conclude that hypoxic incubation increases the relaxation and cAMP production induced by αCGRP 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, αCGRP8–37 showed increased affinity at the CGRP1 receptor during hypoxia, possibly due to a conformational change at the CGRP1 receptor site.
British Journal of Pharmacology (2005) 145, 646–655. doi:10.1038/sj.bjp.0706232
DOI: 10.1038/sj.bjp.0706232
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