Our objective was to evaluate the maternal-fetal transfer of melatonin in pregnant women. Serum melatonin concentration was measured by high-performance liquid chromatography with electrochemical detection in a maternal vein and in the umbilical artery and umbilical vein at the time of birth. Blood samples were obtained from 12 women who had spontaneously delivered vaginally at night. A single oral dose of melatonin was administered to each of 33 patients who underwent a cesarean section, and, blood samples were taken at 1, 2, 3, or 4 hr after the administration of melatonin at delivery. Cesarean section was performed between 1300 and 1500 hr. The mean melatonin concentrations of melatonin in maternal peripheral venous blood and umbilical arterial and umbilical venous blood did not differ significantly, and positive correlations in the serum levels of melatonin were observed between the three sources of blood. The oral administration of 3 mg of melatonin to pregnant women led to marked increases in the serum levels of melatonin, with maximum levels observed 2 hr (21.84 +/- 2.09 ng/ml) after drug administration. Changes in serum levels of melatonin in the umbilical vein and artery resembled those found in the maternal vein. Serum melatonin concentrations did not differ significantly between the maternal vein and the umbilical veins. Serum levels of melatonin in the umbilical vein after the administration of melatonin were significantly and closely correlated with those in the maternal vein (r = 0.924, P < 0.001). These results suggest that, in humans, melatonin is transferred from the maternal to the fetal circulation both easily and rapidly. A potential for the therapeutic use of melatonin as an antioxidant exists in the patients with preeclampsia.

We have cloned the gene encoding RNase HII (RNase HII Pk ) from the hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1 by screening of a library for clones that suppressed the temperature-sensitive growth phenotype of an rnh mutant strain of Escherichia coli. This gene was expressed in an rnh mutant strain of E. coli, the recombinant enzyme was purified, and its biochemical properties were compared with those of E. coli RNases HI and HII. RNase HII Pk is composed of 228 amino acid residues (molecular weight, 25,799) and acts as a monomer. Its amino acid sequence showed little similarity to those of enzymes that are members of the RNase HI family of proteins but showed 40, 31, and 25% identities to those of Methanococcus jannaschii, Saccharomyces cerevisiae, and E. coli RNase HII proteins, respectively. The enzymatic activity was determined at 30°C and pH 8.0 by use of an M13 DNA-RNA hybrid as a substrate. Under these conditions, the most preferred metal ions were Co 2؉ for RNase HII Pk , Mn 2؉ for E. coli RNase HII, and Mg 2؉ for E. coli RNase HI. The specific activity of RNase HII Pk determined in the presence of the most preferred metal ion was 6.8-fold higher than that of E. coli RNase HII and 4.5-fold lower than that of E. coli RNase HI. Like E. coli RNase HI, RNase HII Pk and E. coli RNase HII cleave the RNA strand of an RNA-DNA hybrid endonucleolytically at the P-O3 bond. In addition, these enzymes cleave oligomeric substrates in a similar manner. These results suggest that RNase HII Pk and E. coli RNases HI and HII are structurally and functionally related to one another.

Novel chiral binaphtyl surrogates with an inner hydrogen bond have been created. The NH appears at 13.0-13.3 ppm in thier (1)H NMR spectrum, indicating extremely strong hydrogen bonding. Enantiomers of these compounds were stable at ambient temperature and separable by HPLC with a chiral stationary phase. The half-lives of racemization of the enantiomer are in the range 3 months to 2 years at 20 degrees C, and the barriers for racemization are in the range 27.0 to 28.2 kcal/mol. An X-ray crystal analysis of the compound (R = CHPh(2)) shows that the pseudonaphthyl skeleton including CN...HN is almost completely planar and the dihedral angle between the pseudonaphthalene and naphthalene rings is 128 degrees .

We evaluated the antioxidant property of melatonin as it relates to the vasospastic effect of hydrogen peroxide (H2O2) on the human umbilical artery. Helical sections of umbilical arteries were obtained from healthy pregnant women who were delivered between weeks 37 and 39 of gestation. Changes in maximal potassium chloride (KCl)-induced tension were measured in arterial segments with intact endothelium. Segments were treated with H2O2 alone, or were pretreated either with an H2O2 scavenger (catalase, 2000 i.u.), a hydroxyl radical scavenger (mannitol, 10(-2) M), a nitric oxide-synthesis inhibitor (L-NG-monomethyl arginine, LNMA, 2 x 10(-4) M), or melatonin (10(-6) M to 10(-4) M). The effect of H2O2 (10(-4) M) on the relaxation induced by the calcium ionophore A23187 was also determined in arterial segments, with or without pretreatment with melatonin (10(-6) M, 10(-4) M). H2O2 (10(-6) M to 10(-4) M) potentiated vascular tension in a concentration-dependent manner (P < 0.0001). Pretreatment with LNMA significantly suppressed the vasospastic effect of H2O2 (P < 0.0001). Pretreatment with either catalase or mannitol significantly reduced the vasospastic effect of H2O2 (P < 0.005, P < 0.002, respectively). Melatonin also significantly reduced the vasospastic effect of H2O2 in a concentration-dependent manner (H2O2 10(-6) M, P < 0.0001 : H2O2 10(-5) M, P < 0.0001 : H2O2 10(-4) M, P < 0.00001). Pretreatment with H2O2 significantly inhibited the relaxation induced by the calcium ionophore A23187 (P < 0.005). Treatment with melatonin prior to exposure to H2O2 significantly restored the relaxation induced by A23187 (P < 0.005). Results suggest that H2O2 potentiates vascular tension in the human umbilical artery, perhaps by suppressing the endothelial synthesis of nitric oxide. Melatonin significantly suppressed the vasospastic effect of H2O2, possibly due to its ability to scavenge the hydroxyl radical.