S1PR1 and Thrombocytopenia: One of the many proposed roles of S1P in the blood, through its activation of S1PR1, is a master regulator of efficient thrombopoiesis, as demonstrated in mice where severe thrombocytopenia was observed in a mouse model lacking S1PR1, and activation of the S1P/ S1PR1 signalling promoted the release of new platelets into the bloodstream [236].