1 The purpose of this study was to determine whether endocannabinoids can protect the heart against ischaemia and reperfusion. 2 Rat isolated hearts were exposed to low-flow ischaemia (0.5 -0.6 ml min À1) and reperfusion. Functional recovery as well as CK and LDH overflow into the coronary effluent were monitored. Infarct size was determined at the end of the experiments. Phosphorylation levels of p38, ERK1/2, and JNK/SAPK kinases were measured by Western blots. 3 None of the untreated hearts recovered from ischaemia during the reperfusion period. Perfusion with either 300 nm palmitoylethanolamide (PEA) or 300 nm 2-arachidonoylglycerol (2-AG), but not anandamide (up to 1 mm), 15 min before and throughout the ischaemic period, improved myocardial recovery and decreased the levels of coronary CK and LDH. PEA and 2-AG also reduced infarct size. 4 The CB 2 -receptor antagonist, SR144528, blocked completely the cardioprotective effect of both PEA and 2-AG, whereas the CB 1 -receptor antagonist, SR141716A, blocked partially the effect of 2-AG only. In contrast, both ACEA and JWH015, two selective agonists for CB 1 -and CB 2 -receptors, respectively, reduced infarct size at a concentration of 50 nm. 5 PEA enhanced the phosphorylation level of p38 MAP kinase during ischaemia. PEA perfusion doubled the baseline phosphorylation level of ERK1/2, and enhanced its increase upon reperfusion. The cardioprotective effect of PEA was completely blocked by the p38 MAP kinase inhibitor, SB203580, and significantly reduced by the ERK1/2 inhibitor, PD98059, and the PKC inhibitor, chelerythrine. 6 In conclusion, endocannabinoids exert a strong cardioprotective effect in a rat model of ischaemia -reperfusion that is mediated mainly through CB 2 -receptors, and involves p38, ERK1/2, as well as PKC activation.

Abstract-Growth hormone-releasing peptides (GHRPs) are known as potent growth hormone secretagogues whose actions are mediated by the ghrelin receptor, a G protein-coupled receptor cloned from pituitary libraries. Hexarelin, a hexapeptide of the GHRP family, has reported cardiovascular activity. To identify the molecular target mediating this activity, rat cardiac membranes were labeled with a radioactive photoactivatable derivative of hexarelin and purified using lectin affinity chromatography and preparative gel electrophoresis. A binding protein of M r 84 000 was identified. The N-terminal sequence determination of the deglycosylated protein was identical to rat CD36, a multifunctional glycoprotein, which was expressed in cardiomyocytes and microvascular endothelial cells. Activation of CD36 in perfused hearts by hexarelin was shown to elicit an increase in coronary perfusion pressure in a dose-dependent manner. This effect was lacking in hearts from CD36-null mice and hearts from spontaneous hypertensive rats genetically deficient in CD36. The coronary vasoconstrictive response correlated with expression of CD36 as assessed by immunoblotting and covalent binding with hexarelin. These data suggest that CD36 may mediate the coronary vasospasm seen in hypercholesterolemia and atherosclerosis. Key Words: acute coronary syndromes Ⅲ growth hormone-releasing peptides Ⅲ CD36 scavenger receptor G rowth hormone-releasing peptides (GHRPs) belong to a family of small synthetic peptides modeled from Metenkephalin, which exhibit potent and dose-dependent GHreleasing activity and also significant prolactin (PRL)-and corticotropin (ACTH)-releasing effects. 1 These neuroendocrine activities of GHRPs are mediated by the Ghrelin receptor, a specific G protein-coupled receptor 2,3 that has been cloned from mammalian pituitary libraries and its subtypes identified in the pituitary gland, hypothalamus, and extra-hypothalamic brain regions by binding studies. 4 Equilibrium displacement binding assays with GHRPs in different peripheral tissues have shown specific binding sites in the heart, adrenal, ovary, testis, lung, and skeletal muscle. 5,6 Significantly, hexarelin, a hexapeptide member of the GHRPs family has been reported to feature cardiovascular activity. Long-term pretreatment of GH-deficient rats with this peptide provided protective effect on hearts from ischemia/reperfusion damages 7 and prevented alterations of the vascular endothelium-dependent relaxant function. 8 This protective effect was independent of any stimulation of the somatotropic axis, 8,9 suggesting a direct action of hexarelin on specific cardiac receptors. Our initial characterization of a putative cardiac GHRP receptor revealed the existence of a binding site for a photoactivatable derivative of hexarelin with a M r of 84 000 distinct from those identified in the pituitary. 6,10 In the present study, we report the identification of the unique GHRP binding site in the heart as CD36, a multifunctional B-type scavenger receptor. We also demonstrate that t...

We investigated the mechanisms that are responsible for the basal release of endothelium-derived relaxing factor (EDRF), which is likely to be identical with nitric oxide, in the intact coronary circulation. The increase in cGMP content of platelets passing through the coronary bed of the isolated rabbit heart was used as an index of EDRF release. Platelet cGMP content after passage through the heart under control conditions (flow rate of 20 ml/min) amounted to 0.50 +/- 0.10 pmol/mg protein. Inhibition of endothelial nitric oxide synthesis by 30 microM NG-nitro-L-arginine (L-NNA) reduced this amount by more than 60%. Increasing flow rate from 20 ml/min to 40 and 60 ml/min led to flow-dependent dilation as reflected by the subsequent drop in perfusion pressure after an initial rise. The flow-dependent dilation was associated with a significant increase in the normalized platelet cGMP content. L-NNA abolished completely both the flow-dependent dilation and the increase in platelet cGMP content. Increasing shear stress by a strong vasoconstriction (1 nM endothelin-1) at constant flow was also accompanied by a 2.5-fold increase in platelet cGMP content. To investigate whether mechanical forces applied to the vascular wall by the myocardial contraction cycle were also a stimulus for EDRF release, cardiac arrest was induced by a continuous infusion of mepivacaine (final concentration, 0.02%). Under these conditions, a decrease in platelet cGMP content comparable to that after nitric oxide synthesis inhibition was observed in the arrested heart.(ABSTRACT TRUNCATED AT 250 WORDS)