The role of serotonin in ischemic cellular damage and the infarct size-reducing effect of sarpogrelate, a 5-hydroxytryptamine-2 receptor blocker, in rabbit hearts.

OBJECTIVE: We aimed to clarify the relation between sarpogrelate (SG), a 5-hydroxytryptamine (5-HT)-2 receptor blocker, and myocardial interstitial serotonin or infarct size during ischemia and reperfusion.
BACKGROUND: In cardiac tissues serotonin is rich in vascular platelets, mast cells, sympathetic nerve endings, and the receptors are present in platelets and cardiomyocytes.
METHODS: The myocardial interstitial serotonin levels were measured using a microdialysis technique during 30-min ischemia with and without SG in in vivo as well as isolated rabbit hearts. Other rabbits underwent 30 min of ischemia and 48 h of reperfusion, and the effect of SG on the infarct size was investigated in the absence and presence of a selective protein kinase C (PKC) inhibitor, chelerythrine (5 mg/kg, intravenously), or a mitochondrial adenosine triphosphate sensitive potassium (KATP) channel blocker, 5-hydroxydecanoate (5-HD) (5 mg/kg, intravenously). In another series, the effect of SG on PKC isoforms in cytosol and membrane fraction was assessed after a 20-min global ischemia in isolated rabbit hearts.
RESULTS: Interstitial serotonin levels were markedly increased during 30-min ischemia in in vivo and isolated hearts, and the increases were inhibited by SG in each. The infarct size was reduced by SG (27 +/- 2% vs. 40 +/- 3% of control). This effect was blocked by chelerythrine and 5-HD, respectively. Sarpogrelate further enhanced the ischemia-induced translocation of PKC-epsilon to the membrane fraction.
CONCLUSIONS: Sarpogrelate reduces the myocardial infarct size by inhibiting the serotonin release followed by enhancement of PKC-epsilon translocation and opening of the mitochondrial KATP channel in ischemic myocytes.