Submitted on June 4, 2006
Accepted on November 1, 2006
Hypothermia reduces ischemia- and stimulation-induced myocardial interstitial norepinephrine and acetylcholine releases
Toru Kawada1*, Hirotoshi Kitagawa2, Toji Yamazaki3, Tsuyoshi Akiyama4, Atsunori Kamiya1, Kazunori Uemura1, Hidezo Mori2, and Masaru Sugimachi1
1 Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan
2 Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Osaka, Japan
3 Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Suita, Japan
4 Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan
* To whom correspondence should be addressed. E-mail: torukawa{at}res.ncvc.go.jp.
Although hypothermia is one of the most powerful modulators that can reduce ischemic injury, the effects of hypothermia on the function of the cardiac autonomic nerves in vivo are not well understood. We examined the effects of hypothermia on the myocardial interstitial norepinephrine (NE) and acetylcholine (ACh) releases in response to acute myocardial ischemia and to efferent sympathetic or vagal nerve stimulation in anesthetized cats. We induced acute myocardial ischemia by coronary artery occlusion. Compared to normothermia (n=8), hypothermia at 33°C (n=6) suppressed the ischemia-induced NE release [63 nM (SD 39) vs 18 nM (SD 25), P<0.01] and ACh release [11.6 nM (SD 7.6) vs 2.4 nM (SD 1.3), P<0.01] in the ischemic region. Under hypothermia, the coronary occlusion increased the ACh level from 0.67 nM (SD 0.44) to 6.0 nM (SD 6.0) (P<0.05) and decreased the NE level from 0.63 nM (SD 0.19) to 0.40 nM (SD 0.25), (P<0.05) in the non-ischemic region. Hypothermia attenuated the nerve stimulation-induced NE release from 1.05 nM (SD 0.85) to 0.73 nM (SD 0.73) (P<0.05, n=6) and ACh release from 10.2 nM (SD 5.1) to 7.1 nM (SD 3.4) (P<0.05, n=5). In conclusion, hypothermia attenuated the ischemia-induced NE and ACh releases in the ischemic region. Moreover, hypothermia attenuated the nerve stimulation-induced NE and ACh releases. The Bezold-Jarisch reflex evoked by the LAD occlusion, however, did not appear to be affected under hypothermia.
