Phenotype determination of thiopurine methyltransferase in erythrocytes by HPLC.

These associations also appear to be consistent with the hypothesis that, as a cytokine, S100B exerts a neurotrophic role (1 ), although more extensive studies of the relationships of S100B with other brain constituents will be needed to support this possibility. Previous investigations have reported that amniotic fluid is devoid of detectable S100B in physiological conditions, whereas detectable concentrations can be observed in anencephalic fetuses (9 ). The reason for the discrepancy between these findings and ours of low but measurable S100B concentrations in healthy fetuses is probably attributable to the different limits of detection of the methods used (0.2 mg/L in our study vs 1.5 mg/L for the method used in the previous study). The present data provide reference values for S100B in amniotic fluid during the second trimester of pregnancy, which could constitute a useful tool for the further study of pathological conditions of the nervous system in the early stages of pregnancy. In this respect, the source of a large part of S100B present in the amniotic fluid is probably the fetal nervous system, where the protein has been shown to be present at the ages investigated in the present study, although not at mature concentrations (13–16). On the other hand, it is possible that S100B could also be released, at least in part, from other sites in which it is concentrated, such as adipose tissue, although data on the presence of the protein in adipose tissue at this age are inconclusive. Finally, the possibility that S100B is released from placental tissue as a trophic factor should be taken into account, although its presence in the placenta has not been documented. In any case, the present findings offer preliminary data supporting further investigation of S100B dynamics in vivo, with special reference to a possible role of the protein in fetal brain maturation.