influence of L-carnitine among other agents on the functional recovery of the isolated rat heart exposed to hypoxic cold cardioplegia

ABSTRACT

L-carnitine, is an amino acid derivative, that has previously shown a beneficial effect on skeletal and cardiac muscle function through favorable metabolic effects. This study aims to test for a possible protective effect of L-carnitine in face of cold hypoxic cardioplegia of the isolated rat heart. Sixty male albino rats were used in this study and were divided into six study groups. Isolated rat hearts from all the study groups were exposed to hyperkalemic, hypoxic cold cardioplegia for two hours with the following changes in the cardioplegic solution Group I served as a control group with no special additions to the cardioplegic solution; for Group II, glucose in the cardioplegic solution was increased to a concentration of 22millimole [mM] for Group III methylprednisolone sodium succinate [MPSS] was added to a concentration of 100mg per liter; Group IV received verapamil in the cardioplegic solution at a concentration of 1.1 micromol/L; Group V had L-carnitine at a concentration of 1mM and for Group VI, L-carnitine was added to the cardioplegic solution a t a concentration of 4Mm. The heart rate [HR], Dp/dt, the left ventricular developed pressure [LVDP], and rate pressure product [RPP] were recorded at baseline, and at 15 and 60 minutes after the start of re-warming. Epinephrine was given to the working hearts at doses of 0.5, 1.0 and 2.0 micromol before cardioplegia and after re-warming and the changes in cardiac function parameters in response to epinephrine were recorded. Creatine phosphokinase [CPK] was measured in samples from the coronary effluent taken before cardioplegia and 15 minutes after re-warming. The control group showed a significant reduction in all cardiac function parameters after cardioplegia and re-warming [dp/dt[max], LVDP and RPP reached 40.2%, 18.8% and 8.4% of their baseline values respectively]. Significant cardiac protection was noted in the groups exposed to glucose and carnitine. Functional recovery with glucose reached 66.2% of the baseline value for the dp/dt[max], 55.2% for the LVDP and 17.5% for the RPP [p<0.01 as compared to control]. Functional recovery with carnitine 4mM reached 98.7% of the baseline value of dp/dt[max], 89.9% for the LVDP, 48.1% for the RPP [p<0.05 as compared to all the other groups]. For carnitine at the 4mM concentration the dp/dt[max] values at the end of the experiment showed no significant difference from the baseline values. Also the percentage increase in dp/dt[max] and LVDP in response to post-cardioplegic epinephrine showed no significant difference from that recorded before cardioplegia [p>0.05]. MPSS provided only transient cardiac improvement compared to the control group, while verapamil showed no protective action on cardiac function parameters. CPK results showed significantly lower post re-warming CPK with all the tested drugs