Influence of vagotomy on changes in feline plasma catecholamine levels induced by occlusion of either the left or right coronary vessel

The purpose of this study was two-fold: (1) to determine the effect of occlusion of the left anterior descending branch (LAD) of the left coronary artery or the right coronary (RC) artery on plasma catecholamine levels, and (2) to determine whether bilateral vagotomy has an effect on changes in plasma catecholamine levels evoked by coronary occlusion. Chloralose anaesthetised cats subjected to LAD occlusion exhibited increases in plasma noradrenaline and adrenaline at 3 min post-occlusion. The increases in noradrenaline and adrenaline were unrelated to the hypotension that occurred at this time. Bilateral vagotomy did not appear to alter the effect of LAD occlusion on catecholamine release into the circulation but did unmask a significant correlation between the degree of hypotension and the magnitude of increase in plasma catecholamines. Right coronary occlusion in animals with intact and sectioned vagus nerves evoked noradrenaline and adrenaline release that was significantly correlated with a fall in arterial pressure. Bilateral vagotomy per se caused an increase in baseline plasma catecholamine levels. Pretreatment with atropine mimicked the increase in baseline catecholamine levels seen with vagotomy. These results indicate that occlusion of the LAD and RC arteries increase the release of catecholamines into the circulation. The role of the vagus nerves in this response was observed only with LAD occlusion and consisted of altering the relationship between the degree of hypotension and the magnitude of increase in plasma catecholamines. That is, after vagotomy, the decrease in blood pressure following LAD occlusion was effective in causing release of catecholamines, presumably because of the hypotension causing a decrease in baroreceptor stimulation. Finally, it appeared that vagotomy increases the release of noradrenaline into the circulation by removing efferent vagal tone that inhibits noradrenaline release. This inhibitory action is mediated by activation of muscarinic receptors.