Association of pathological tyrosine isoforms with parameters of hematopoiesis in hyperfiltrating physiological pregnant women Imre Tormási1, Szilárd Kun2, Gergő A. Molnár2, Attila Miseta3, András Szilágyi1, István Wittmann2 1 Department of Obstetrics and Gynecology, Kaposi Mór Teaching Hospital, Kaposvár 2 2nd Department of Medicine and Nephrological Centre, University of Pécs, Faculty of Medicine, Pécs 3Department of Laboratory Medicine, University of Pécs, Pécs, Hungary Objective: Hyperfiltration and lowering of hemoglobin level are documented changes in physiological pregnancy. Serum level of erythropoietin (EPO) increases in pregnancy and EPO-resistance develops. Elevation of the concentration of hydroxil radical¬–derived, pathological products of phenylalanine (Phe) as meta- and ortho-tyrosine (m-Tyr, o-Tyr) in contrast to physiological p-Tyr could have a role in the development of EPO-resistance. Serum level of p-Tyr may decrease in hyperfiltration. Methods and participants: Twenty-three physiological pregnant women and 26 healthy, non-pregnant women were enrolled. We determined the concentrations of Phe and the three Tyr isoforms. The time kinetics of these and their association with hematopoiesis were studied. Results: At the beginning of the pregnancy hyperfiltration and decreased serum level of p-Tyr were developed (p < 0.05). Afterwards, in progression of the pregnancy, both p-, m-, o-Tyr and Phe levels showed an increasing tendency (p < 0.05). Serum levels of m- and o-Tyr and their ratios with Phe and p-Tyr correlated inversely with hemoglobin level (p < 0.05). In linear regression analyses, these amino acid parameters were independent predictors of hemoglobin level (p < 0.05). Urinary excretion of p-Tyr showed an increasing tendency (p < 0.05). Urinary levels of o-Tyr and its ratios with Phe and p-Tyr correlated with red cell distribution width and were predictors of it (p < 0.05). Conclusions: Elevated levels of pathological Tyr isoforms and decreased concentration of p-Tyr are associated with hematopoiesis in physiological pregnancy. Lowered level of p-Tyr can be the result of increased excretion or elevated consumption. We propose that pathological tyrosines may lead to disturbed erythropoiesis.