1. The effects of cocaine on neutral amino acid uptake by human placental basal membrane vesicles
J M Dicke, D K Verges, K L Polakoski Am J Obstet Gynecol. 1994 Aug;171(2):485-91. doi: 10.1016/0002-9378(94)90287-9.
Objective: Prior studies have demonstrated that cocaine binds to human placental microvillous membrane vesicles at a single high-affinity site and that both 10 and 500 nmol/L cocaine inhibit sodium-dependent alanine uptake. The purpose of this study was to characterize cocaine binding to human placental basal plasma membrane and to determine the effects of cocaine on basal vesicle uptake of alanine and leucine. Study design: Basal vesicles were isolated from the placentas of uncomplicated human pregnancies with no history of cocaine use. The binding of tritiated cocaine to basal vesicle membrane and the uptakes of tritiated cocaine, alanine, and leucine were determined with filtration assays. Alanine and leucine uptakes were measured in the presence and absence of sodium and 10 and 500 nmol/L cocaine. Cocaine binding was characterized with Scatchard analyses, and uptakes were compared by means of Student t tests. Results: Tritiated cocaine bound to basal membrane at two separate high-affinity sites. Sodium-dependent alanine uptake was significantly inhibited only by 500 nmol/L cocaine. Sodium-independent amino acid uptake was unaffected by cocaine. Conclusion: Cocaine may interfere with fetal growth by impairing the activity of sodium-dependent amino acid transporters in both the microvillous and basal membrane. These membranes may be differentially sensitive to the effects of cocaine on such transporters.
2. Fetoplacental growth and placental protein synthesis in rats after chronic maternal cocaine administration
A S Salhab, C L DeVane, T Medrano, W C Buhi, I R Tebbett, K T Shiverick J Pharmacol Exp Ther. 1994 Jul;270(1):392-8.
This study evaluated the effects of chronic exposure to cocaine during pregnancy on the morphology and function of the placenta. Pregnant rats received either 45 or 60 mg/kg of cocaine hydrochloride by i.p. injection as a divided daily dose on days 8 to 18 of gestation. The maternal weight gain decreased by 20% to 24% (P < .05) in the two cocaine treatment groups, whereas the placental weight was not significantly altered. Fetal growth showed a dose-related decrease in the 45- and 60-mg/kg cocaine treatment groups; fetal body weights and length were significantly decreased by 5% to 10%. The plasma levels of cocaine were 0.79 and 1.09 micrograms/ml in the 45- and 60-mg treatment dose groups, respectively; the level in the fetal plasma was 3-fold higher in the latter group. Placental tissue explants were cultured in the presence of [35S]-methionine to investigate whether cocaine exposure altered placental protein synthesis. Secreted proteins were analyzed by polyacrylamide gel electrophoresis followed by fluorography or by western blotting and immunostaining with antibodies to placental prolactin-like proteins-B and -C and growth hormone-related protein-1. The data showed that there were no quantitative or qualitative changes in placental peptide hormone secretion as a result of the cocaine treatment. These data indicate that chronic cocaine exposure in the pregnant rat is associated with fetal growth retardation in the absence of alterations in placental morphology or secretory protein synthesis.
3. Glutamine transport in human and rat placenta
D A Novak, M J Beveridge Placenta. 1997 Jul-Aug;18(5-6):379-86. doi: 10.1016/s0143-4004(97)80037-9.
Glutamine plays an important role in fetal nutrition. This study explored the transport of [3H]glutamine into apical and basal predominant membrane vesicles derived from rat and human placenta. Na+-dependent glutamine transport was present in both apical and basal predominant vesicles derived from 20- and, to a lesser degree, 14-day gestation rat placenta. Amino-acid transport systems A, ASC-like, B(o,+) (in apical membrane vesicles) and, perhaps, y+L were involved in Na+-dependent glutamine transport. Na+-dependent glutamine uptake into human placental microvillus and basolateral membrane vesicles also occurred via several distinct transport activities. Glutamine transport via system N was not detected in either rat or human placental preparations. Na+-dependent glutamine transport in the rat was more pronounced in basal as compared to apical membrane vesicles. Conversely, in the human preparations, activity was significantly higher in microvillus as compared to basolateral membrane vesicles. It is concluded that Na+-dependent glutamine transport occurs through a variety of transport agencies in both the rat and human placenta. Transport varies with ontogeny and between species.
