Endogenous myocardial norepinephrine is not essential for ischemic
preconditioning in the rabbit heart.
Ardell, Jeffrey L., Xi-Ming Yang, Barbara A. Barron, James M. Downey,
and Michael V. Cohen.
Departments of Physiology and Medicine, University of South
Alabama, Mobile, AL 36688 and Department of Physiology, University of
North Texas Health Science Center, Fort Worth, TX 76107
APStracts 2:0371H, 1995.
To determine if endogenous cardiac catecholamines mediate ischemic
preconditioning (PC) in the rabbit heart, myocardial catecholamines
were depleted by reserpine (5 mg/kg, 18-24 hrs pre-PC) or surgical
sympathectomy (2 wks pre-PC). In vivo hearts were subjected to 30 min
of regional ischemia and 3 hr of reperfusion. PC involved either 1 or
4 cycles of 5-min ischemia/10-min reperfusion prior to the 30-min
ischemic period. Right ventricular norepinephrine content (pmol/mg
protein), 51.4+/-11.1 in untreated rabbits, was reduced to 0.6+/-0.2
and 1.8+/-0.5 by surgical sympathectomy and reserpine, respectively.
Infarct size (IS) was measured by tetrazolium and expressed as % of
the risk zone. In untreated animals exposed solely to 30 min of
regional ischemia IS was 35.5+/-1.6%, and was unchanged by reserpine
(43.3+/-5.4%) or surgical sympathectomy (33.4+/-3.5%). When compared
to infarction in the respective non-PC controls, IS in untreated
(7.4+/-1.5%, p<0.0001) and surgically sympathectomized (11.2+/
-1.5%, p<0.0001) animals was significantly diminished by a single
cycle of PC, but the latter exerted less protection in reserpinized
animals (27.6+/-3.5%, p<0.0025). Four cycles of PC, however,
reduced IS to 10.3+/-1.2% in reserpinized animals. Therefore, despite
comparable depression of myocardial norepinephrine content, surgical
and chemical sympathectomy had different effects on the level of
protection afforded by ischemic PC. These data demonstrate that
endogenous myocardial catecholamines are not essential for protection
from PC in the rabbit.
Received 5 June 1995; accepted in final form 16 August 1995.
APS Manuscript Number H512-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 August 1995.