Endothelin-1 causes long-lasting contraction via endothelin type A receptor (ETAR) in isolated rat mesenteric arteries (RMA) that cannot be readily terminated by removing the agonist, or by adding the ETAR antagonist BQ123 or the NO donor sodium nitroprusside. It could be terminated by adding calcitonin-gene related peptide (CGRP), most likely because CGRP causes ET-1/ETAR dissociation. Here we investigated this phenomenon in human coronary microarteries (HCMA). We simultaneously verified the effects of CGRP in RMA and HCMA towards other vasoconstrictors, i.e., the α1-adrenoceptor agonist phenylephrine, the thromboxane A2 analog U46619 (9,11-dideoxy-11α,9α-epoxy-methano-prostaglandin F2α) and KCl. Long-lasting contraction (remaining after washing away the agonist) was observed for ET-1 in RMA, but not HCMA. Constrictions to phenylephrine, U46619 or KCl did not last upon washing. When added on top of ET-1-initiated contraction in RMA, CGRP effectively counteracted vasoconstriction, i.e., it caused full relaxation. Inhibitory effects of CGRP were also observed when briefly exposing RMA and HCMA to CGRP 1h before the addition of ET-1. Similar inhibitory effects of transient CGRP pre-incubation were seen towards phenylephrine, U46619 or KCl in RMA and HCMA. In conclusion, our data imply that CGRP, like ET-1, causes long-lasting effects that remain apparent up to 1h after its removal from the organ bath. Thus, in addition to the reported dissociation of ET-1/ETAR complexes, CGRP causes long-lasting non-selective arterial smooth muscle relaxation that may add to the neuropeptide being a physiological antagonist of arterial effects of ET-1. Long-lasting, washout-resistant ET-1/ETAR interaction does not occur in HCMAs.
European Journal of Pharmacology, 2013, Vol 720, Issue 1-3, p. 303-9