The potentiation of sinus arrhythmia by vasoactive intestinal polypeptide (VIP) in the anaesthetized dog.
Vasoactive intestinal polypeptide (VIP) is a neuropeptide released from the vagus, which in contrast to acetylcholine has a long-acting positive chronotropic effect on the heart. The aim of this study, in the anaesthetized dog, was to examine the effects of VIP and a VIP antagonist when injected into the sinus node artery of a vagally intact heart in sinus arrhythmia. The response was compared to that produced by noradrenaline (NAD) infusion and stimulation of the sympathetic nerves to the heart. Mean +/- S.D. of 30 R-R intervals was used to describe mean heart rate interval and heart rate variability. VIP, a VIP antagonist, NAD and sympathetic nerve stimulation all caused increases in heart rate without significant increases in blood pressure. However, only VIP caused an increase in heart rate variability; VIP antagonism and NAD caused a decrease and sympathetic nerve stimulation had no effect. These results suggest that VIP and acetylcholine when released from the vagus act synergistically to increase sinus arrhythmia.
Markos
F
F
Department of Physiology, University College Cork, Ireland. hazim@ucc.ie
Snow
H M
HM
D000320:Adrenergic Fibers / Q000378:metabolism; D000818:Animals; D001146:Arrhythmia, Sinus / Q000378:metabolism*; D004285:Dogs / Q000502:physiology*; D004558:Electric Stimulation; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism / Q000494:pharmacology*
D010446:Peptide Fragments; D013566:Sympathomimetics; D014660:Vasoactive Intestinal Peptide; D009638:Norepinephrine