MBTPS1 and ischemia: To test whether signaling by S1P receptors was causally involved in cardioprotection by platelet-released S1P in SNT+ and if so, whether it acted directly on the heart rather than systemically, we analyzed the effect of SNT+ and SNT− in a Langendorff model of global ischemia, where cardioprotective effects on local cardiac cells can be assessed without effects on systemic immune cell responses.