There is increasing evidence that
reactive oxygen species (ROS) contribute to post-ischemic
reperfusion injury, but determination of the specific ROS involved has proven elusive. In the present study electron paramagnetic resonance (EPR) spectroscopy was used in vitro to measure the relative quenching of
singlet oxygen (1O2) by
histidine and
carnosine (beta-alanyl-
L-histidine) utilizing the hindered secondary
amine 2,2,6,6-tetramethyl-4-piperidone HCl (4-oxo-TEMP). The relative effect of
histidine and
carnosine on functional recovery of isolated perfused rat hearts was also studied. Functional recovery was measured by left ventricular developed pressure (LVDP), first derivative of left ventricular pressure (dP/dt), heart rate (HR) and coronary flow (CF). EPR measurements and Stern-Volmer plots showed that 400 microM
carnosine quenched 1O2 twice as effectively as equimolar
histidine in vitro. Moreover, 10 mM
histidine improved functional recovery of isolated rat hearts significantly more than 1 mM
histidine. Furthermore, 1 mM
carnosine improved functional recovery significantly more than equimolar
histidine and as effectively as 10 mM
histidine. Experiments with 1 mM
mannitol, a known
hydroxyl radical scavenger, did not show an improvement in functional recovery relative to control hearts, thereby decreasing the likelihood that
hydroxyl radicals are the major damaging species. On the other hand, the correlation between improved functional recovery of isolated rat hearts with
histidine and
carnosine and their relative 1O2 quenching effectiveness in vitro provides indirect evidence for 1O2 as ROS participating in
reperfusion injury.