Effects of an HMG-CoA reductase inhibitor in combination with an ACE inhibitor or angiotensin II type 1 receptor antagonist on myocardial metabolism in ischemic rabbit hearts

Cardioprotection with pioglitazone is abolished by nitric oxide synthase inhibitor in ischemic rabbit hearts--comparison of the effects of pioglitazone and metformin

BACKGROUND

The effects of two drugs representing different classes of antidiabetic pharmacology (pioglitazone, a thiazolidinedione; and metformin, a biguanide) on the myocardial metabolism in the ischemia are poorly understood.

METHODS

To test the hypothesis that cardioprotection of pioglitazone and metformin is associated with nitric oxide (NO), we studied the high energy phosphate metabolism by 31P-nuclear magnetic resonance (NMR) in isolated rabbit hearts. Forty-five minutes of continuous normothermic global ischemia was carried out. Pioglitazone or metformin was administered at the beginning, 60 min prior to the global ischemia, with or without the nitric oxide synthase inhibitor, L-NAME, administered 5 min or 60 min prior to the ischemia. In the first experiment, whether NO was produced or not by administration of pioglitazone, for the prevention of myocardial ischemic injury, was investigated. Hearts of male Japanese white rabbits were divided into 4 experimental groups: the control (C) group, the P group consisting of pioglitazone treatment, the P + L5 group consisting of pioglitazone treatment with L-NAME (5 min before ischemia), and the P + L60 group consisting of pioglitazone treatment with L-NAME (60 min before ischemia). In the next experiment, a comparison between the effects of pioglitazone and metformin in preventing ischemic injury were studied. The hearts were divided into 4 experimental groups: the control (C) group, the P group consisting of pioglitazone treatment, the P + L5 group consisting of pioglitazone treatment with L-NAME (5 min before ischemia), the M group consisting of metformin treatment, and the M + L5 group consisting of metformin treatment with L-NAME (5 min before ischemia).

RESULTS

In the first experiment, the decrease in adenosine triphosphate (ATP) during ischemia was significantly inhibited in the P group in comparison with the C group (P < 0.01). However, the decrease in ATP was not inhibited in the P + L5 group during ischemia. In contrast, in the P + L60 group, the decrease in ATP was not inhibited during a part of ischemia. In the next experiment, a comparison between the effects of pioglitazone and metformin in preventing ischemic injury was studied. As a result of administration of either pioglitazone or metformin, there was no difference between groups with and without L-NAME.

CONCLUSION

These results suggest that pioglitazone has a significant beneficial effect on improving the myocardial energy metabolism during ischemia. This cardioprotection may be dependent on nitric oxide (NO) synthase during ischemia more than preischemia. Furthermore, the present findings suggest that both pioglitazone and metformin have equal cardioprotective effects mediated by NO on myocardial ischemic injury in rabbits.

Cardioprotection by metformin is abolished by a nitric oxide synthase inhibitor in ischemic rabbit hearts

We investigated the effects of metformin on myocardial metabolism during ischemia by 31P-nuclear magnetic resonance (NMR) in isolated rabbit hearts. Metformin was administered 60 min prior to induction of global ischemia, or in combination with a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), at 5 min or 60 min prior to the ischemia. Normothermic global ischemia was then carried out for 45 min. Twenty-eight hearts were divided into 4 experimental groups consisting of 7 hearts each: a control (C) group; an M group receiving metformin treatment alone; an M+L (5) group receiving metformin treatment with L-NAME at 5 min before ischemia; and an M+L (60) group receiving metformin treatment with L-NAME at 60 min before ischemia. During ischemia, the decrease in adenosine triphosphate (ATP) was significantly inhibited in the M group in comparison with the C group (p < 0.01). However, this preservation of ATP in the M group was inhibited in the M+L (5) group during ischemia. In contrast, in the M+L (60) group, this preservation of ATP in the M group was not inhibited during, but not at the end of, ischemia. These results suggest that metformin has a significant beneficial effect for improving the myocardial energy metabolism during myocardial ischemia. This cardioprotection may be more dependent on nitric oxide synthase during ischemia than during pre-ischemia.