title: Pituitary adenylate cyclase-activating polypeptide: localization and differential influence on isolated hearts from rats and guinea pigs.
abstract: This study was done to determine if pituitary adenylate cyclase-activating peptide (PACAP)-immunoreactive nerve fibers occur in cardiac muscle as well as intracardiac ganglia of rats and guinea pigs and to clarify the chronotropic actions of PACAP27 in the same species using isolated heart preparations. PACAP nerve fibers were not detected in atrial or ventricular muscle of rat or guinea pig but a few stained nerve fibers occurred in the atrioventricular bundle of the guinea pig. Stained nerve fibers were prominent in intracardiac ganglia of both species. PACAP27 caused a dose-dependent tachycardia in isolated rat hearts (+39 +/- 3 beats/min with 1 nmol, n = 6). Positive and/or negative chronotropic responses were evoked by PACAP27 in guinea pig heart, depending on dose and prior exposure to the peptide. PACAP27 also caused arrhythmias in several guinea pig hearts. Treatment with atropine eliminated or prevented PACAP-evoked bradycardia and arrhythmias, implicating cholinergic neurons in these responses. Positive chronotropic responses to PACAP were unaffected by beta-adrenergic receptor blockade in either species, suggesting that tachycardia resulted from a direct action on the heart. These observations support the conclusion that endogenous PACAP could have a role in regulating parasympathetic input to the heart but through different mechanisms in rats versus guinea pigs. A direct positive chronotropic influence of endogenous PACAP is unlikely since atrial muscle lacks PACAP-immunoreactive nerve fibers.
authors.affiliation: Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University Johnson City, TN 37614, USA.
authors.forename: Yingzi
authors.initials: Y
authors.lastname: Chang
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Lawson
authors.forename: John C
authors.initials: JC
authors.lastname: Hancock
authors.forename: Donald B
authors.initials: DB
authors.lastname: Hoover
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D006168:Guinea Pigs; D006325:Heart Atria / Q000166:cytology / Q000294:innervation / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology / Q000294:innervation / Q000378:metabolism*; D007120:Immunochemistry; D008297:Male; D009412:Nerve Fibers / Q000378:metabolism*; D009414:Nerve Growth Factors / Q000096:biosynthesis* / Q000494:pharmacology; D009479:Neuropeptides / Q000096:biosynthesis* / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000096:biosynthesis* / Q000494:pharmacology; D009924:Organ Culture Techniques; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D051381:Rats; D013045:Species Specificity; D013610:Tachycardia / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology
chemical_list: C495403:Adcyap1 protein, rat; D009414:Nerve Growth Factors; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide