The effects of cocaine on neutral amino acid uptake by human placental basal membrane vesicles

Fetal effects of cocaine: an updated meta-analysis

BACKGROUND

A very large number of women in the reproductive age group consume cocaine, leading to grave concerns regarding the long term health of millions of children after in utero exposure. The results of controlled studies have been contradictory, leading to confusion, and, possible, misinformation and misperception of teratogenic risk.

OBJECTIVE

To systematically review available data on pregnancy outcome when the mother consumed cocaine.

METHODS

A meta-analysis of all epidemiologic studies based on a priori criteria was conducted. Comparisons of adverse events in subgroups of exposed vs. unexposed children were performed. Analyses were based on several exposure groups: mainly cocaine, cocaine plus polydrug, polydrug but no cocaine, and drug free.

RESULTS

Thirty three studies met our inclusion criteria. For all end points of interest (rates of major malformations, low birth weight, prematurity, placental abruption, premature rupture of membrane [PROM], and mean birth weight, length and head circumference), cocaine-exposed infants had higher risks than children of women not exposed to any drug. However, most of these adverse effects were nullified when cocaine exposed children were compared to children exposed to polydrug but no cocaine. Only the risk of placental abruption and premature rupture of membranes were statistically associated with cocaine use itself.

CONCLUSIONS

Many of the perinatal adverse effects commonly attributed to cocaine may be caused by the multiple confounders that can occur in a cocaine using mother. Only the risk for placental abruption and PROM could be statistically related to cocaine. For other adverse effects, additional studies will be needed to ensure adequate statistical power.

Cocaine up-regulates norepinephrine transporter binding in the rat placenta

We investigated the influence of 3 days of continuous cocaine exposure on norepinephrine transporter binding in the rat placenta. On gestational day 17, pregnant rats were implanted subcutaneously with two cocaine-containing Silastic capsules. There were two control groups, one that received capsules with vehicle only and was pair-fed to the cocaine-treated females, and a second group that was untreated and fed ad libitum. Placentas and fetal brains were harvested and frozen on gestational day 20, and subsequently subjected to saturation analyses for norepinephrine transporter binding using the selective ligand [3H]nisoxetine. There was a marked increase in the density (B(max)) of norepinephrine transporter binding sites in the placentas of the cocaine-treated animals compared to both control groups, but no change in the fetal brain. The mechanism underlying this up-regulation of the placental norepinephrine transporter is not yet known, but it could involve a beta-adrenoceptor- and cAMP-mediated induction of transporter gene expression.

Maternal cocaine use and cigarette smoking in pregnancy in relation to amino acid transport and fetal growth

This review covers the weight of evidence that shows the association of cocaine and cigarette smoking in pregnancy with the impaired transplacental amino acid transport which might give rise to fetal growth restriction (IUGR). Vasoconstrictive effects of both cocaine and nicotine on the placental vasculature are clearly not the only cause for inhibition of placental amino acid uptake and transfer. In vitro studies strongly suggest that cocaine decreases the activity of placental amino acid transport system A and system N, and possibly system l and system y(+), while nicotine decreases the activity of system A. These findings are supported by cordocentesis studies in human IUGR pregnancies not resulting from drug abuse. More work is needed to be done in order to understand the potential additive or synergistic effect of cocaine and cigarette smoking on fetal growth and to determine the underlying cellular mechanisms of interaction with placental amino acid transporters.

[Consequences of cocaine addiction during pregnancy on the development in the child]

Cocaine facilitates neurotransmitter release from the central nervous system, decreases their re-uptake at the synapse junction level and increases their blood level due to receptors blockade. During pregnancy cocaine inhibits uterine adrenergic beta receptors and easily crosses the placenta, the main obstetrical consequences of overstimulation of the noradrenergic system being miscarriage, retroplacental haematoma, ruptured uterus, short and premature labour. Fetal and neonatal consequences resulting from both a decreased uterine blood flow and a direct effect of cocaine on fetal development can be severe. Decreased uterine blood flow lowers oxygen and nutriment transport which in turn can induce intra-uterine growth retardation. The direct effect of cocaine on the fetus is responsible for an increased catecholamine plasma concentration leading to vasoconstriction episodes, increased heart rate and blood pressure, and subsequent oxygen requirement. Several malformations have been reported, sometimes severe (involving central nervous system, heart, digestive tract, urinary tract and bone) that are mainly due to fetal circulation failure. Cocaine can also directly alter brain development because of neuronal mistargeting within the cerebral cortex.

Effect of chronic cocaine administration on amino acid uptake in rat placental membrane vesicles

This study evaluated the effects of chronic exposure to cocaine during pregnancy on amino acid uptake in placental membrane vesicles. Pregnant rats received 62 mg/kg of cocaine hydrochloride by intraperitoneal (IP) injection as a divided daily dose on gestation days 8-19 inclusive. Fetal body weights were significantly decreased by 19% in the cocaine group, while placental weights were unchanged. Placental apical membrane vesicles were prepared from control and cocaine-treated animals, and marker enzyme enrichments for alkaline phosphatase and [3H]-dihydroalprenolol binding did not differ between cocaine and control groups. Rates of uptake (10 sec) of selected radiolabeled amino acids were measured utilizing a rapid filtration technique. Na(+)-dependent apical membrane [3H]-glutamine transport (50 microM) was reduced by 95% (p < 0.05) in cocaine-treated compared to control placentas. Uptake of 50 microM [3H]-methyl aminoisobutyric acid (MeAIB) into apical membranes was also decreased by 43% (p < 0.05) in cocaine membranes. Na(+)-independent [3H]-arginine transport (10 microM), however, did not differ between control or cocaine-treated groups. In summary, chronic cocaine administration selectively inhibited the transport of glutamine and MeAIB into apical membrane vesicles, but had minimal effect on arginine transport. We postulate that this diminution in uptake may contribute to the fetal growth retardation noted in our model.