Is endogenous erythropoietin a pathogenetic factor in the development of essential hypertension?

Background. Recent experimental studies have found that erythropoietin elicits vasoconstriction and proliferation of endothelial cells. We conducted the following study to assess the possible interactions between endogenous erythropoietin, systemic and renal haemodynamics at different stages of essential hypertension. Methods. We examined 47 patients with borderline essential hypertension (age 26+/-3 years) and 49 patients with established essential hypertension WHO stage I-II (age 52+/-10 years), and compared them to 42 normotensive individuals (age 26+/-3 years). The concentration of erythropoietin (radioimmunoassay), 24-h ambulatory blood pressure (Spacelab 90207), systemic haemodynamics (Doppler sonography) and renal haemodynamics (para-aminohippuric acid and inulin clearance) were determined. Results. Erythropoietin was within normal range and similar among the three groups. In patients with established essential hypertension, a close correlation was found between erythropoietin and systolic (r=0.45, P<0.002) and diastolic (r=0.51, P<0.001) ambulatory blood pressure. In contrast, ambulatory blood pressure was not correlated with erythropoietin in subjects with borderline hypertension. Total peripheral resistance (r=0.41, P<0.02) was linked to erythropoietin in established but not in borderline hypertension. However, erythropoietin was inversely correlated with renal plasma flow in both established and borderline hypertension (r=-0.33, P<0.05, and r=-0.34, P<0.05 respectively). In normotensive subjects, in contrast, erythropoietin was not correlated with any of the determined variables. In neither group erythropoietin was linked to the haematocrit or hemoglobin concentration. Conclusion. The correlation between erythropoietin and renal vascular changes which is already present in borderline hypertension and is confirmed in established hypertension indicates an involvement of erythropoietin in the development of essential hypertension. The presence of normal concentrations of endogenous erythropoietin in all groups suggests a dysregulation of erythropoietin in patients with essential hypertension as the pathophysiological link between erythropoietin and vascular changes.