Abstract
Isolated porcine myocardial trabeculae from right atria and left ventricles were paced at 1.5 Hz in tissue baths, and changes in isometric contractile force upon exposure to agonist were studied. Alpha calcitonin gene-related peptide (α-CGRP) increased contractile force in nearly half of the trabeculae, whereas the selective CGRP2 receptor agonist [Cys(acetylmethoxy)2,7]-CGRP had effect in only a few. Preincubation with the CGRP1 receptor antagonist α-CGRP-(8-37) (10−6 M) almost completely blocked positive inotropic responses to α-CGRP. Amylin had weak positive inotropic effects in some atrial, but not in ventricular trabeculae. Adrenomedullin did not affect contractility in either atrial or ventricular trabeculae. In conclusion, these results suggest that α-CGRP has a positive inotropic effect that can be mediated by both CGRP1 and CGRP2 receptors. Amylin seems to have a potential positive inotropic effect on atrial tissue, whereas no direct effect of adrenomedullin could be measured.
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