title: Rate of acetylcholine hydrolysis affects the phase dependency of cardiac responses to vagal stimulation.
abstract: The influence of the rate of acetylcholine hydrolysis on the magnitude and phase dependency of the cardiac chronotropic response to vagal stimulation was studied in anaesthetised dogs. In one group of animals the chronotropic response to tonic vagal stimulation varied directly with the dose of physostigmine. In a second group of animals one brief stimulus burst was delivered to the right vagus nerve during each cardiac cycle, and the timing (phase) of the stimulus was varied within the cycle. Before physostigmine was given the phase of the stimulus had a substantial influence on the chronotropic response. When each stimulus burst contained 6 pulses the response was changed from its minimum to its maximum value (mean (SEM) change 0.338(0.081) s) when the phase was shifted by a mean value of 0.091(0.031) s. After physostigmine (0.3 mg X kg-1) was given the change in response produced by a phase shift was much less pronounced. A mean shift in phase of 0.593(0.052) s was required to change the chronotropic response from its minimum to its maximum value, and the mean difference between the minimum and maximum response was only 0.140(0.032) s. Hence the rate of acetylcholine hydrolysis in the cardiac tissues is an important determinant of the phase dependency of the chronotropic response to repetitive vagal stimulation-that is, the slower the rate of hydrolysis the less the change in the chronotropic response elicited by a given change in stimulus timing.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D004285:Dogs; D004558:Electric Stimulation; D006321:Heart / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects; D006868:Hydrolysis; D009206:Myocardium / Q000378:metabolism*; D010830:Physostigmine / Q000494:pharmacology; D013268:Stimulation, Chemical; D013997:Time Factors; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D010830:Physostigmine; D000109:Acetylcholine