TPO is synthesized predominantly by the liver parenchymal cells, but it is also produced in smaller amounts by the kidneys and bone marrow stromal cells. The synthesis of TPO is constitutive, meaning it is produced continuously. However, its regulation is mainly post-translational. The level of circulating platelets inversely affects TPO levels - when platelet counts are low, more TPO is available to stimulate megakaryocyte activity; conversely, when platelet counts are high, TPO is sequestered by platelets, reducing its availability.
