Hiroyasu Hisanaga

Characterization of Human Placental Activity for Transport of L-alanine, Using Brush Border (Microvillous) Membrane Vesicles

The uptake of taurocholate into brush border membrane vesicles prepared from human full term placenta was studied using a rapid filtration technique. The taurocholate uptake into brush border membrane vesicles was sensitive to extravesicular osmolarity, and pre-incubation of the brush border membrane vesicles with the taurocholate increased the uptake of taurocholate into the brush border membrane vesicles. These findings indicate that the uptake of taurocholate by brush border membrane vesicles represents transport into vesicles. The uptake of taurocholate into vesicles was not dependent on Na+ electrochemical gradient (extravesicular > intravesicular). But this uptake was markedly increased when the intravesicular space was rendered electrically more positive by the use of lowly permeant anions or valinomycin-induced K+ diffusion membrane potentials. These findings indicate that the taurocholate transport into brush border membrane vesicles was dependent on membrane potential. The initial rate of taurocholate transport into brush border membrane vesicles exhibited saturation kinetics with respect to the taurocholate concentration, an apparent Km of 67 microM and Vmax of 0.30 nmol/mg protein/20 sec were calculated.

Platelet Aggregation Inhibition Activity of Placental Brush Border Membrane

Thrombus occurs frequently in the placental chorionic lumen of patients with Pre-ecclampsia (EPH) gestosis, and participation of platelets is suggested in the pathology of the diseases. In the placental tissues, there is an antiplatelet aggregating factor which plays an important role in the maintenance of microcirculation in the placenta. The brush border membrane of the placental chorioepithe-lium plays the part of the vasoendothelium as it is the point of direct contact with the maternal blood flow in the chorionic lumen. It has already been confirmed that a strong inhibitory action on platelet aggregation is present in the vasoendothelium, and its main active mechanism is shown to be prostacyclin (PG I2) and ADP degrading by an ADPase-like activity which exists in edothelial membrane. Thus, it is quite possible that some inhibitory activity on platelet aggregation exists in the brush border membrane of placental chorioepithelium. We, therefore, investigated the presence of such an inhibitory activity on platelet aggregation as well as its properties using a fraction of the brush border membrane.

EVALUATION OF EXTRA-UTERINE ADAPTATION OF PREMATURE NEONATES AND IUGR INFANTS BASED ON HbF SWITCHING

The switching of HbF to HbA was observed in 40-week AFD infants. Four weeks post partum HbF was 65%, decreasing to 50% at eight weeks. Premature neonates, however, took 3 weeks longer to reach a similar level. This phenomenon in premature neonates is thought to be related to their immaturity. To determine whether the HbF switching ratio of IUGR infants is also lower m than that of normal infants, C-leucine was adminstered to HbF in red blood cells in umbilical blood to judge by the synthesis ratio. The synthesis ratio in 28-week premature neonates was 91%, significantly higher than the 65% ratio of term infants. In IUGR infants as well, the ratio of 73% indicated an obvious delay in HbF switching compared with term AFD infants. Moreover, the concentration of 2,3DPG in IUGR infants was often low at birth, also indicating a delay in extra-uterine adaptation. With IUGR neonates it was found that HbF switching to HbA was delayed and in most cases there was a low concentration of 2,3DPG, which enhances oxygen supply to the tissues. These two factors indicate that IUGR infants have a lower capacity for extrauterine adaptation than normal infants.