Effects of brief ischaemia on myocardial acetylcholine and noradrenaline levels in anaesthetized cats

Although brief ischaemic events make the myocardium tolerant to subsequent prolonged ischaemia, known as ischaemic preconditioning, whether brief ischaemia also affects neural regulation at the in vivo heart remains unknown. We examined the effects of brief ischaemia on myocardial interstitial acetylcholine (ACh) and noradrenaline (NA) levels in anaesthetized cats (n=6). Baseline ACh and NA levels were 0.65±0.13 and 0.66±0.17 nmol l−1 (mean±SE), respectively. Two sets of 5-min brief occlusion followed by 20-min reperfusion of the left anterior descending coronary artery (LAD) significantly increased the myocardial interstitial ACh level to 4.6±0.7 nmol l−1 (P<0.01), while not affecting the myocardial interstitial NA level. Subsequent 60-min LAD occlusion significantly increased the ACh and NA levels to 34.9±6.0 and 96.5±17.0 nmol l−1 (P<0.01), respectively. Vagotomy abolished the myocardial interstitial ACh release during brief ischaemia and attenuated the ACh release during subsequent 60-min ischaemia (n=6). In contrast, vagotomy did not affect the subsequent ischaemia-induced myocardial interstitial NA release. We conclude that the brief ischaemia affects myocardial interstitial ACh release but not NA release in the ischaemic myocardium in vivo.