A. Banerjee et al., PRECONDITIONING AGAINST MYOCARDIAL DYSFUNCTION AFTER ISCHEMIA AND REPERFUSION BY AN ALPHA-1-ADRENERGIC MECHANISM, Circulation research, 73(4), 1993, pp. 656-670
Preconditioning may find ready applicability in humans facing schedule
d global cardiac ischemia-reperfusion (IR) during bypass or transplant
ation, where such a maneuver is feasible before arrest. Our objective
was to delineate and exploit the endogenous preconditioning mechanism
triggered by transient ischemia (TI) and thereby attenuate myocardial
postischemic mechanical dysfunction by clinically acceptable means. Pr
econditioning by 2 minutes of TI followed by 10 minutes of normal perf
usion protected isolated rat left ventricle function assessed after 20
minutes of global, 37-degrees-C ischemia and 40 minutes of reperfusio
n. Final recovery of developed pressure (DP) was improved (91.5+/-1.9%
of equilibration DP versus unconditioned IR control, 57.4+/-2.4%, P<.
01) and was accompanied by increased contractility (+/-dP/dt). Norepin
ephrine release increased after TI, and reserpine pretreatment abolish
ed TI preconditioning. This suggests that endogenous norepinephrine me
diates functional preconditioning in rat. Brief pretreatment (2 minute
s) with exogenous norepinephrine reproduced the protection (89.1+/-1.4
%) of postischemic function. Functional protection persisted after the
hemodynamic effects had resolved. Norepinephrine-induced precondition
ing was simulated by phenylephrine and blocked by alpha1-adrenergic re
ceptor antagonist. TI preconditioning was similarly lost after selecti
ve alpha1-adrenergic receptor blockade. We conclude that transient isc
hemic preconditioning is mediated by the sympathetic neurotransmitter
release and alpha1-adrenergic receptor stimulation. Although the postr
eceptor mechanism remains unclear, functional protection after IR does
not seem related to the magnitude of ATP depletion and elevation of r
esting pressure during ischemia. Rather, the endogenous mechanisms fac
ilitate both recovery of mechanical function and ATP repletion during
reperfusion.