title: FMRFamide inhibition of a molluscan heart is accompanied by increases in cyclic AMP.
abstract: The molluscan neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) inhibits the beat of isolated ventricles of the freshwater clam Lampsilis claibornensis. The decline in frequency and diastolic tone precedes the dose- and time-dependent increase in cAMP also produced by the peptide. Phosphodiesterase inhibitors (theophylline, 3-isobutyl-1-methylxanthine) and cAMP analogs also inhibit Lampsilis hearts, but only at high doses (10(-5)-10(-3)M). Again, the inhibition by theophylline is accompanied by a rise in cAMP. Nevertheless, the delayed increase in cAMP levels following FMRFamide treatment may suggest that cAMP is not mediating the onset of FMRFamide cardioinhibition.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism*; D019835:FMRFamide; D006321:Heart / Q000187:drug effects; D008974:Mollusca / Q000502:physiology*; D009842:Oligopeptides / Q000008:administration & dosage / Q000494:pharmacology*; D013806:Theophylline / Q000494:pharmacology
chemical_list: D009842:Oligopeptides; D019835:FMRFamide; D013806:Theophylline; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine