416 Placenta (I 991), Vol. 12

different in the SGA vesicles (SGA = 1.2 f 0.18 nmol/mg protein, n = 8, and AGA = 1.7 t 0.73 nmoVmg protein, n = 7).

Sodium-dependent MeAIB uptake at 1 min was significantly (P = 0.02) lower in SGA vesicles (0.02 + 0.005 nmol/mg protein, n = 3) compared to AGA vesicles (0.06 + 0.011 nmol/mg protein, n = 5).

These preliminary results suggest that Na+/H+ exchange is normal in SGA placentas, while MeAIB uptake is reduced, in agreement with the study of Dicke and Henderson, 1988, Am. 3. Med. Sci., 295,223-227. (Supported by NWRHA.)

MICHONDRIAL GLUTAMINE AND GLUTAMATE METABOLISM IN HUMAN PLACENTA AND ITS POSSIBLE LINK WITH PROGESTERONE BIOSYNTHESIS W. Makarewicz, J. Klimek &J. S wierczyriski (Department of Biochemistry, Medical School, ul. Debinki 1, 80-211 Gdansk, Poland)

Glutamine seems to be the preferred substrate for energy production in highly proliferative tissues and glutamate is the only amino acid which shows a net uptake from the umbilical circulation into the placenta. We have shown previously that placental motochondria possess the ability to metabolize glutamine and glutamate to ammonia and lactate. Experimental data indicate that this pathway involves deamination of glutamine to glutamate and deamination of glutamate to oxoglutarate. The carbon skeleton of glutamine can be converted via the tricarboxylic acid cycle to malate and further to pyruvate and lactate (glutaminolysis). Our experiments revealed that human placental mitochondria contain the specific enzymes involved: glutaminase (EC.3.5.1.2) and NAD(P)-dependent malic enzyme (EC.1.1.1.39). Their kinetic properties have been investigated together with the effect of substrate concentration, pH, inorganic phosphate and divalent cations.

The effect of glutamine and glutamate on the rate of conversion of “C-cholesterol to 14C- progesterone in placental mitochondria has been studied, the results indicate that glutamine and glutamate metabolism support progesterone biosynthesis. The possible regulatory link between mitochondrial glutamine and glutamate metabolism and the progesterone biosyn- thesis lies in the supply of reducing equivalents (NADPH) produced by the glutamate dehydrogenase NAD(P)-dependent malic enzyme and isocitrate dehydrogenase.

CHARACTERIZATION AND LOCALIZATION OF ENDOTHELIN BINDING SITES ON TROPHOBLAST AND VASCULARIZATION OF HUMAN PLACENTA A. Malassine, F. Mondon, C. Robaut’, M. Vialb, G. Tanguy, W. Rosteneb & F. Ferrt (INSERM U.166, 75014 Paris et Laboratoire de Physiologie Cellulaire URA CNRS 290, Universite de Poitiers, a Rhone-Poulenc Sante, 94403 Vitry-sur-Seine and b INSERM U.339,75012 Paris, France)

Endothelins are endothelium-derived 21 amino acid peptides with unusually potent vaso- constrictor actions. Regarding their endocrine and paracrine activities, endothelins can also be considered as peptide hormones and growth factors. Specific receptors for endothelin-1 (ET- 1) have been previously detected and purified in crude human placental preparations

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(Fischi et al, 1989; Wilkes et al, 1990; Wada et al, 1990). So, for fine receptor characteriz- ation and localization, we have investigated ‘*‘I ET-1 binding on morphologically and physiologically well-defined placental components. Stem villi vessel membranes (S.V.M.), membranes of cultured trophoblast (T.C.M.), microvilli of syncytiotrophoblast (M.V.) and fetal facing syncytial basal membranes (B.M.) were used for binding studies. Very high affinity and specific binding sites for ‘*‘I ET-l were identified on these placental prep- arations. Scatchard analysis of binding data revealed Kd values of 26 f 4 pM (n = 6) for S.V.M., 126 + 4pM (n = 3) for T.C.M., 23 f pM (n = 3) for M.V., and 12 + 2 pM (n = 3) for B.M. with maximum binding capacities of 68 ? 60 (n = 6) 224 + 53 (n = 3) 40 + 19 (rl = 3) and 147 + 5 (n = 3) fmol/mg proteins respectively. The binding of **‘I ET-l was antagonized by cold ET- 1 and ET-3. These data demonstrate that ET- 1 binding sites are more numerous on fetal facing basal plasma membrane than on the maternal facing microvilli of the syncytiotrophoblast. Placental cryostat sections (2Opm) and cultured trophoblast were processed for “in vitro” receptor autoradiography. In placental sections, autoradiography showed the association of numerous grains on the smooth cells of vessels and on the trophoblastic layer of the chorionic villus. In cultured trophoblast, treated for autoradiogra- phy, labeling is observed mainly on cellular aggregates and on multinucleated syncytiotro- phoblast. Labeling was abolished by coincubating “‘1 ET-l with an excess of unlabelled ET-1 (1 /&I).

These results suggest that ET-l intervene in regulation of placental vascular resistance and in the physiology of the trophoblast.

PLACENTAL TRANSPORT OF IgG ACROSS THE IN VITRO PERFUSED HUMAN PLACENTA A. Malek, E. Aegerter, R. Sager & H. Schneider (Department of Obstetrics/Gynecology, University of Beme, Beme, Switzerland)

Immunoprotection of the human fetus and newborn is based on maternal antibodies transmitted to the fetus across the placenta during the last weeks of pregnancy. The receptor- mediated mechanism is restricted to IgG antibodies and is dependent on an intact Fc portion of the molecule.

The understanding of IgG transport across the human placenta may open new possibilities for intrauterine therapy in the presence of maternal infections such as Hepatitis B and HIV or irregular maternal blood group or platelet antibodies.

We investigated transport and release of IgG using the in vitro perfusion of the human placenta. Determination of IgG concentration in perfusion fluids was performed by Partigen@ Immunodiffusion Plate or ELISA. In a first set of three experiments with closed perfusion circuit on maternal and fetal side, the washout or release by the perfused tissue was determined. After 3 h, the IgG concentration in the maternal circuit was 126 f 37 (s.d.) mg/ 1. This corresponded to five times the concentration found in the fetal circuit.

In the second set of three experiments, after a closed circuit control phase of l-2 h, fresh medium was used in both circuits and human IgG (10 g/l) and 14C-BSA (5 &i) were added to the maternal side. After 4-6 h, the fetal concentrations for IgG and 14C-BSA were 1.2, 0.5,0.8 and 0.5, 0.1,0.6 per cent ofthe maternal level. While the difference between IgG and albumin transfer as shown by the final concentrations in the fetal circuit may not be striking, there was a clear difference in the pattern oftransfer. Some 14C-BSA activity was detectable