Serum immunoreactive erythropoietin in hyper- and hypothyroidism: clinical observations related to cell culture studies.

Laboratory experiments have demonstrated that tetra- and triiodothyronine (T4, T3) enhance hypoxia-induced erythropoietin (Epo) production. In the present study serum immunoreactive Epo was measured in 29 patients with hyperthyroidism and in 10 patients with hypothyroidism. Epo levels were inversely correlated to the blood haemoglobin concentration [Hb] in both groups of patients. However, Epo levels at given [Hb] were significantly higher in the hyperthyroid state. In vitro studies confirmed that T4 and T3 stimulate Epo synthesis in the human liver cell line HepG2. This stimulating effect persisted for at least 1 day after the removal of T4 and T3 from the cultures. Thus, while thyroidal disorders affect steady-state levels of circulating Epo, it seems unlikely that thyroid hormones play a major role in abrupt adjustments of Epo production, such as the diurnal changes.