Effect of haemoglobin and endogenous erythropoietin on hypothalamic-pituitary thyroidal and gonadal secretion: an analysis of anaemic (high EPO) and polycythaemic (low EPO) patients.

Abstract

Correction of anaemia with recombinant human erythropoietin (rHu-EPO) improves the responsiveness of thyroidal and gonadal axes to exogenous TRH and GnRH in chronic haemodialysis patients, but the mechanisms remain to be fully elucidated. In order to assess the influences of endogenous erythropoietin on the hypothalamo-hypophyseal thyroidal and gonadal axes, we studied the response of polycythaemic and anaemic patients, in comparison to normal controls, after the administration of exogenous TRH and GnRH. Exogenous hypothalamic factors, 500 micrograms TRH and 100 micrograms GnRH, were administered as a bolus and blood samples were obtained over a 3-hour period at 30, 60, 90, 120 and 180 minutes. Five male polycythaemic patients (low EPO), three male anaemic patients (high EPO) and six normal age and sex matched controls were studied. Blood samples were centrifuged immediately and the serum was stored at -20 degrees C until assayed for total T4, free T4, free T3, TSH, prolactin, growth hormone (TRH test), and FSH, LH, testosterone (GnRH test). Haematological parameters and biochemical profiles were also measured. After TRH administration, both patient groups showed a normal TSH response; however, their free T4 and free T3 secretion was blunted compared to controls. Normal basal PRL levels increased in an exaggerated fashion, whereas, when compared to chronic renal failure patients on chronic haemodialysis, we did not see a paradoxical GH response or a basal GH increase in these 5 patients. GnRH administration in the study groups elicited a normalization in the LH response without an increase in testosterone levels; however, an exaggerated FSH response was found in the polycythaemic patients (low EPO). Thus by investigating the role of low endogenous EPO levels in non-anaemic and anaemic patients with high EPO levels, our study suggests that the underlying chronic disease state may be the major contributing factor in the regulation of the hypothalamo-hypophyseal thyroid and gonadal axes, rather than the EPO levels.