The effectiveness of ischemic preconditioning on myocardial protection and comparison with K(+) cardioplegia

KP-102 (growth hormone-releasing peptide-2) attenuates ischemia/reperfusion injury in isolated rat hearts

KP-102, a synthetic growth hormone (GH)-releasing peptide, exerts a variety of effects on cardiac function. In the present study, we investigated the direct cardiac effects of KP-102 with regard to ischemia/reperfusion injury by using isolated rat hearts. Isolated Wistar rat hearts were mounted on a Langendorff apparatus and subjected to 30 min of ischemia followed by 40 min of reperfusion. The rat hearts were treated with 0.1-10 nmol/l KP-102 beginning from 15 min before ischemia until the end of the experiment, with the exception of the ischemia period. Cardiac parameters such as the left ventricular end-diastolic pressure (LVEDP), left ventricular developed pressure (LVDP), maximum dP/dt (+dP/dtmax), minimum dP/dt (-dP/dtmax), and heart rate (HR) were measured. The following ischemia/reperfusion-induced cardiac dysfunctions were observed: increased LVEDP and decreased LVDP, +dP/dtmax, and -dP/dtmax. KP-102 at a dose of 0.1 nmol/l or more induced lower LVEDP and higher LVDP and gave higher +dP/dtmax and -dP/dtmax values during the reperfusion as compared with the control groups. In particular, KP-102 at 10 nmol/l clearly suppressed the increase in the LVEDP after reperfusion; eventually, the LVEDP was restored to the preischemia level. At 40 min of reperfusion, 10 nmol/l KP-102 noticeably increased the LVDP, +dP/dtmax, and -dP/dtmax, as compared with the control. KP-102 had no effect on the HR throughout the experiment. In conclusion, KP-102 improved cardiac function in rat isolated hearts subjected to ischemia/reperfusion injury, which is independent of GH secretion.

Cardioprotection by St Thomas' solution is mediated by protein kinase C and tyrosine kinase

BACKGROUND

Intracellular signaling pathways, specifically the activation of protein kinase C and tyrosine kinase, are essential to the cardioprotection of ischemic preconditioning. We proposed that activation of PKC and TK contribute to the myocardial protection of St. Thomas' No. 2 cardioplegia solution (STC).

MATERIALS AND METHODS

Isolated rat hearts were exposed to 40 min of global ischemia followed by 120 min of reperfusion. Before ischemia, hearts received no treatment (control; n = 7), STC (n = 7), phorbol 12-myristate 13-acetate (PMA; n = 6), PMA + chelerythrine (n = 6), anisomycin (n = 6), anisomycin + genistein (n = 7), STC + chelerythrine (n = 7), STC + genistein (n = 7), PMA + genistein (n = 7) or anisomycin + chelerythrine (n = 7). Left ventricular developed pressure (LVDP) recovery, myocardial infarct size, and lactate dehydrogenase release were measured.

RESULTS

STC as well as PMA (protein kinase C activator) and anisomycin (tyrosine kinase activator) significantly reduced infarct size (6.9 +/- 2.9%, 9.6 +/- 2.1%, 14.0 +/- 4.4%) compared with controls (42.4 +/- 2.9%, P < 0.05). The infarct reduction of PMA and anisomycin were blocked by their inhibitors chelerythrine and genistein, respectively. Both chelerythrine (29.2 +/- 4.1%, P < 0.05) and genistein (40.4 +/- 4.3%, P < 0.05) attenuated the reduction of infarct size provided by STC. The recovery of LVDP improved with STC, PMA and anisomycin (72.6 +/- 1.4%, 60.4 +/- 4.7%, 57.2 +/- 4.6%) compared with control (33.8 +/- 3.6%, P < 0.05). Addition of chelerythrine or genistein to STC impaired recovery of LVDP (52.3 +/- 4.4%, 35.1 +/- 2.5%, P < 0.05) compared with STC treatment.

CONCLUSION

Administration of the pharmacologic inhibitors chelerythrine and genistein blunts the cardioprotection caused by STC treatment.