In contrast, direct exposure of MPCs to high EPO did not lead to changes in intracellular calcium (Supplementary Fig. 5A and B), clearly suggesting that EPO would not directly influence epinephrine exocytosis; rather, it is systemic hypoglycemia secondary to EPO-induced erythrocytosis in mice that enhances adrenal epinephrine release. This evidence concerns the gene EPO and polycythemia.