Inexpensive Apple Macintosh-Based Electrocardiography in Small Animals

Exogenous GSH protection during hypoxia-reoxygenation of the isolated rat heart: impact of hypoxia duration

The objective of this study was to determine the interaction between duration of myocardial hypoxia and presence of exogenous glutathione (GSH) on functional recovery upon subsequent reoxygenation. Isolated perfused rat hearts were subjected to 20, 30, 40, or 50 min hypoxia (HYP), which resulted in a progressive decline in the amount of contractile recovery (% of normoxic rate-pressure product (RPP) and developed pressure) during 30 min reoxygenation. Supplementation with 5 mM GSH throughout normoxia, hypoxia, and reoxygenation significantly improved contractile recovery during reoxygenation after 20 and 30 min hypoxia (p < 0.05), but had no effect after longer durations of hypoxia when contractile recovery was typically below 40% of RPP and significant areas of no-reflow were observed. ECG analysis revealed that GSH shifted the bell-shaped curve for reperfusion ventricular fibrillation to the right resulting in attenuated fibrillation after 20 and 30 min hypoxia then increased incidences after 40 min when Control hearts were slow to resume electrical activity. ECG conduction velocity was well preserved in all hearts after 20 and 30 min hypoxia, but GSH administration significantly attenuated the decline that occurred with longer durations. GSH supplementation did not attenuate the 35% decline in intracellular thiols during 30 min of hypoxia. When 5 mM GSH was added only during 40 min of hypoxia, RPP recovery after reoxygenation was improved compared to unsupplemented Controls (73% vs. 55% of pre-hypoxia value, p < 0.05). Administration of GSH only during reoxygenation following 40 min of hypoxia did not alter RPP recovery compared to Control hearts. We conclude that cardioprotection by exogenous GSH is dependent on the duration of hypoxia and the functional parameter being evaluated. It is not due to an enhancement of intracellular GSH suggesting that exogenous GSH acts extracellularly to protect sarcolemmal proteins against thiol oxidation during the phase of hypoxia when oxidative stress is a major contributor to cardiac dysfunction. Furthermore, if enough damage accrues during oxygen deprivation, supplementing with GSH during reoxygenation will not impact recovery.

Effects of pharmacological interventions on emetine cardiotoxicity in isolated perfused rat hearts

The cardiotoxicity of emetine continues to be a significant clinical problem. The purpose of this study was to investigate the effect of several mechanistic interventions, including ICRF-187, an iron-chelating agent which protects against doxorubicin toxicity, atropine, and fructose-1,6-bisphosphate (FBP) on the toxicity of emetine in our isolated, perfused rat heart model. The model includes functional, electrocardiographic, and biochemical determinations in the same preparation. Atropine and ICRF-187 had no effect on the time needed for emetine to induce ventricular asystole, while FBP significantly increased this time. Administration of 47 microM atropine, 300 microM FBP, or 1 mM FBP decreased the release of lactate dehydrogenase (LDH) into the coronary effluent, while ICRF-187 had no effect. These pharmacological interventions variably changed the amplitude of the biphasic response of the coronary flow to emetine. Finally, FBP was very effective in slowing the rate of QRS-waveform degeneration in the perfused hearts. Emetine caused PR- and QRS-prolongation which was not altered by FBP.