Endocrine Abstracts

Peptidyl growth hormone secretagogues (GHS), including ghrelin and growth hormone releasing peptides (GHRPs), have been reported to exert cardioprotective effects in experimental models of ischemia-reperfusion (I/R) injury through GH-independent pathway. Along this line, we have identified CD36 as a main target for GHRP binding and action in the heart. Yet, not much is known regarding the molecular mechanisms of the cardioprotective effects of GHRPs. The objective of this study is to dissect the relative role of GHS-R1a and CD36 signaling in cardioprotection using both pharmacologic and genetic approaches. The effects of the selective CD36 ligand (EP 80317) and of hexarelin, a dual CD36 and GHS-R1a agonist, were assessed in murine myocardial I/R. Pretreatment of wild-type (WT) C57BL/6 mice for 2 weeks with either EP 80317 (300 μg/kg) reduced the infarct size in isolated hearts by 75% (P<0.05), following ex vivo global ischemia (30 min)/reperfusion (90 min). In contrast, no effect of the peptides were observed in CD36-null mice, suggesting that CD36 may play a cardioprotective role against I/R-elicited cardiac injury. One of the mechanism by which GHS may contribute to reduce myocardial I/R is by preventing early cardiomyocyte loss through apoptosis. In the present study, we investigated the effect of EP 80317 (300 μg/kg) and of hexarelin (100 μg/kg) on downstream effectors of the signaling pathways of PI3K/Akt in a model of transient (30 min) left coronary artery ligation in isoflurane-anaesthetized WT mice. After 6-h of reperfusion, Akt phosphorylation increased by 44% (P<0.001) and 8% (NS) in EP 80317- and hexarelin-treated mice, respectively. Phosphorylation of Akt was not enhanced in treated CD36-null mice. These results support a critical role for CD36 in mediating GHRP cardioprotective effect, at least in part through the PI3K/Akt signaling mechanisms leading to the phosphorylation and activation of Akt.