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Title: The autonomic nervous system and the heart
Author: Barnes, Jane Yvonne
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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The mechanism by which the release of acetylcholine from cholinergic neurones in the heart is regulated are not well understood. A reliable and sensitive assay for acetylcholine is lacking. An HPLC method was also set up for the measurement of noradrenaline in coronary effluent samples from perfused, innervated rat hearts. The sensitivity was 0.5nM noradrenaline (inter-assay coefficient of variation, 4.9%). Four repeated left stellate ganglion stimulations (5 Hz, 60s, 0.8 mA), S1-S4, separated by a 15 min recovery period, demonstrated a progressive decline in noradrenaline overflow. The influence of duration of ganglion stimulation (30 or 60s) and coronary flow rate (5 or 10 ml g-1 min-1) on the noradrenaline overflow and functional response to four consecutive sympathetic ganglion stimulations, was examined. Baseline (pre-stimulation) mechanical performance of the preparation was stable. Lactate production was low and did not vary significantly between the groups. Stimulation induced changes in heart rate and left ventricular pressure were stable throughout the four stimulations (coronary flow rate 5 ml g-1 min-1). Noradrenaline overflow and contractility, however, showed a progressive decline from S1 to S4 (p<0.05). Reducing the stimulus duration from 60 to 30s delayed the onset of the decline in noradrenaline overflow and +dP/dt, while preventing the decline in the magnitude of the -dP/dt response. Increasing the coronary flow rate, completely prevented the decline in the response to nerve stimulation. In conclusion, vagal stimulation of the perfused, innervated rat heart results in marked negative inotropic and chronotropic changes, without detectable acetylcholine overflow. Repeated left stellate ganglion stimulation (S1-S4) results in reduced noradrenaline overflow and haemodynamic effects, that can be prevented using a coronary perfusion flow rate of 10 ml g-1 min-1. Left stellate ganglion stimulation does not confer a protective effect against ischaemia. Future studies of the role of the parasympathetic nervous system require more sensitive methods to detect acetylcholine.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available