Interactive effects of k&, acid, norepinephrine and ischemia on
cardiac performance: implications for exercise.
Paterson, Mark O'neill Claire E. Sears & David J.
University Laboratory of Physiology, Parks Road, Oxford, OX1 3PT,
UK, tel 01865 272518, fax 01865 282170, e-mail
DJP@physiol.ox.ac.uk
APStracts 3:0538A, 1996.
We tested the hypothesis that cardiac ischemia uncouples the
beneficial interaction among hyperkalemia, acidosis and raised plasma
catecholamines when these chemicals are changed to mimic their
exercise levels. Potassium chloride, lactic acid and norepinephrine
(NE) were infused intravenously for 2 minutes into anesthetised,
artificially ventilated, thoracotomised rabbits during either
occlusion of the left circumflex artery (3 minutes n=10) or following
a period of prolonged ischemia (20 minutes n=7) that led to a small
infarct. Norepinephrine (1[mu]g/kg/min i.v) offset the negative
cardiac effects of hyperkalemia (up to 8.7+/-0.7mM) and acidosis
(arterial pH 7.09+/-0.03) in normal hearts. Cardiac performance was
not significantly depressed by either acute or chronic ischemia prior
to any infusions. However, the protective effect of NE during acute
ischemia or following prolonged ischemia with hyperkalemia and
acidosis was substantially reduced. These results show that cardiac
ischemia attenuates the protective action of NE and increases the
depressive effects of hyperkalemia and acidosis. Whether myocardial
ischemia amplifies the cardiotoxic effects of hyperkalemia and
acidosis during vigorous exercise by attenuating the beneficial
effect of catecholamines remains to be determined.
Received 4 September 1996; accepted in final form 14 November
1996.
APS Manuscript Number A856-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996