Masaru Yonezawa

Comparison of plasma concentrations of arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) in normal and preeclamptic pregnancies.

The study was undertaken to measure both plasma arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) concentrations in normal and preeclamptic pregnancies to elucidate the mechanisms of plasma volume regulation during pregnancy. The mean plasma AVP concentration in healthy pregnant women was much lower than nonpregnant controls; however, the concentration in preeclamptic patients was similar to that in the comparative period of normal pregnancy. Despite volume expansion, the mean plasma concentration of ANP in normal pregnancy showed no changes compared to nonpregnant controls. The concentration of plasma ANP in patients complicated by mild preeclampsia was higher than that in normal pregnant women. The concentration of plasma ANP in those with severe preeclampsia was much higher roughly in proportion to the severity of the disease. It is inferable that the lowered concentration of plasma AVP is involved in plasma volume expansion in normal pregnancy, largely but not in a depletion of plasma volume in preeclampsia. The elevated concentration of plasma ANP appears to be closely related to impaired plasma volume expansion in preeclampsia.

Developmental Changes of Glutamate Dehydrogenase Activity in Rat Liver Mitochondria and Its Enhancement by Branched-Chain Amino Acids

The developmental changes of glutamate dehydrogenase activity in the fetal and neonatal rat liver were investigated, as well as the effects of branched-chain amino acids on this enzyme. Hepatic glutamate dehydrogenase activity showed a marked increase at the end of the fetal period and peaked on the 5th day of neonate at approximately 3 times higher than the adult level. Glutamate dehydrogenase was activated by leucine, isoleucine, and valine in this order when they were added to isolated intact liver mitochondria in vitro. The enhancement of enzyme activity was more marked in fetal rats than in adults. In contrast, when branched-chain amino acids were added after disrupting the mitochondrial membrane by sonication, only leucine slightly activated glutamate dehydrogenase, while isoleucine and valine slightly inhibited its activity. Our findings suggest that glutamate may be actively synthesized in the developing rat liver mitochondria and then transaminated to other nonessential amino acids for protein synthesis, and that increased intramitochondrial branched-chain amino acid concentrations may enhance glutamate dehydrogenase activity. This anabolic metabolism will contribute to the fetal growth and development.

Developmental Changes of Polyamine Biosynthesis in Rat Liver

To investigate the role of polyamine metabolism in fetal development, we determined the hepatic polyamine content and the activity of enzymes related to polyamine metabolism in fetal, newborn and adult rats. In the fetuses, spermidine was detected at the highest level, followed by spermine and then putrescine. Putrescine and spermidine levels were higher in the fetuses than in adult rats, while the spermine level was significantly lower in the fetuses. The activities of the enzymes investigated were also higher in the fetuses than in adult rats. These findings indicate that polyamine synthesis was enhanced in the fetal liver, and that degradation of spermidine via spermidine N1-acetyltransferase contributes to the increase in putrescine levels. Thus, our study suggests that an increase in putrescine is important for fetal growth and that putrescine per se has a significant role in fetal cellular proliferation.

Alterations of red blood cells' polyamines during pregnancy and neonatal period.

Red blood cell polyamines were measured using high-performance liquid chromatography. Spermidine and spermine continued to increase with pregnancy and retained a high level during 24-35 weeks of gestation, then decreased at term; putrescine, however, kept the low nonpregnant level during pregnancy and puerperium. At delivery, umbilical blood showed a significantly higher polyamine level than maternal blood (p less than 0.005 or p less than 0.001). In the neonatal period, each polyamine showed a slight increase on the 1st day after birth, then spermidine and spermine decreased day by day, but putrescine kept the same level. Alterations of polyamines seemed to have some relation to the erythropoiesis in bone marrow and rapid cell proliferations.