title: Effects of moderate hypothermia on in situ cardiac sympathetic nerve endings.
abstract: Although hypothermia is known to alter neuronal control of circulation, it has been uncertain whether clinically used hypothermia (moderate hypothermia) affects in situ cardiac sympathetic nerve endings. We examined the effects of moderate hypothermia on cardiac sympathetic nerve ending function in anesthetized cats. By use of a cardiac dialysis technique, we implanted dialysis probes in the midwall of the left ventricle and monitored dialysate norepinephrine (NE) levels as an index of NE output from cardiac sympathetic nerve endings. Hypothermia (27.0+/-0.5 degrees C) induced decreases in dialysate NE levels. Dialysate NE levels did not return to the control level at normothermia after rewarming. Dialysate NE response to inferior vena cava occlusion was attenuated at hypothermia but restored at normothermia after rewarming. Dialysate NE response to high K(+) (100 mM) was attenuated at hypothermia and was not restored at normothermia after rewarming. Hypothermia induced increases in dialysate dihydroxyphenylglycol (DHPG) levels. There were no differences in desipramine (neuronal NE uptake blocker, 10 microM) induced increment in dialysate NE level among control, hypothermia, and normothermia after rewarming. However, hypothermia induced an increase in DHPG/NE ratio. These data suggest that hypothermia impairs vesicle NE mobilization rather than membrane NE uptake. We conclude that moderate hypothermia suppresses exocytotic NE release via central mediated reflex and regional depolarization.
authors.affiliation: Department of Anesthesia, Nagahama City Hospital, 526-8580, Nagahama, Japan. hirotosi@mx.biwa.ne.jp
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Kitagawa
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Akiyama
authors.forename: Toji
authors.initials: T
authors.lastname: Yamazaki
mesh_terms: D000818:Animals; D001794:Blood Pressure; D001831:Body Temperature; D002415:Cats; D003251:Constriction, Pathologic; D003956:Dialysis; D004947:Esophagus / Q000503:physiopathology; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate; D006358:Hot Temperature; D007035:Hypothermia / Q000503:physiopathology*; D008297:Male; D009206:Myocardium / Q000378:metabolism; D009411:Nerve Endings / Q000503:physiopathology*; D009638:Norepinephrine / Q000378:metabolism; D012016:Reference Values; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014682:Vena Cava, Inferior
chemical_list: D009638:Norepinephrine