Cocaine up-regulates norepinephrine transporter binding in the rat placenta

doi:10.1016/S0014-2999(99)00624-X

European Journal of Pharmacology

Volume 386, Issue 1, 10 December 1999, Pages 1-6

https://doi.org/10.1016/S0014-2999(99)00624-X Get rights and content

Abstract

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 β-adrenoceptor- and cAMP-mediated induction of transporter gene expression.

Introduction

Specific transporter proteins located on nerve terminal plasma membranes are responsible for the clearance of norepinephrine, dopamine, and serotonin (5-hydroxytryptamine, 5-HT) after their release into the synaptic cleft (Amara and Kuhar, 1993). Norepinephrine and 5-HT transporters have also been identified in the placentas of several species. Studies by Ganapathy et al. (1993) found these transporters on brush-border membranes purified from human placenta, which suggests monoamine uptake from maternal blood. In contrast, work by Bzoskie et al. (1995) in sheep clearly demonstrated that the placenta plays a major role in catecholamine clearance from the fetal circulation.

Recent studies of the rat placenta in our laboratory have characterized and localized the binding of [³H]nisoxetine to the norepinephrine transporter (Shearman and Meyer, 1998) and of [¹²⁵I]3-[4-iodophenyl]tropane-2-carboxylic acid methyl ester ([¹²⁵I]RTI-55) and [³H]paroxetine to the 5-HT transporter (Shearman et al., 1998) using both membrane-binding and autoradiographic techniques. Membrane-binding studies showed a much greater abundance of norepinephrine compared to 5-HT transporters in normal rat placenta at gestational day 20. Autoradiographic localization experiments demonstrated high-affinity radioligand binding in both the basal (junctional) zone and labyrinth of the placenta, although the distribution was different for the two transporters.

One important feature of monoamine transporters is that they are blocked by cocaine. Indeed, it is possible that blockade of placental transporters mediates some of the adverse effects of maternal cocaine use on pregnancy outcome and offspring development Ramamoorthy et al., 1993, Prasad et al., 1994. Yet, little is known about the influence of cocaine on placental transporter regulation. Bzoskie et al. (1997) recently reported that women with pregnancy complications, including cocaine use in some cases, showed large elevations in umbilical cord plasma norepinephrine concentrations, and that placental mRNA for the norepinephrine transporter was inversely related to umbilical cord norepinephrine levels. On the other hand, there are no previous studies examining the specific effect of cocaine on placental transporter expression either in humans or laboratory animals.

In the present study, we investigated the influence of cocaine administration from gestational day 17 to gestational day 20 on rat placental norepinephrine transporter binding. We used a Silastic capsule treatment regimen originally developed by Lipton et al. (1991) and previously shown in our laboratory to produce a down-regulation of striatal dopamine transporter binding in offspring at postnatal day 10 (Collins and Meyer, 1996). Because of the possibility of differential regulation in fetus compared to placenta, we also measured the effects of cocaine on whole-brain transporter binding in fetuses obtained from the same dams.

Section snippets

Chemicals

[³H]Nisoxetine (78.4 or 80 Ci/mmol) was purchased from Dupont/New England Nuclear (Boston, MA) and stored at −20°C. Cocaine HCl and mazindol were obtained from Sigma (St. Louis, MO) and Research Biochemicals (Natick, MA), respectively. Cocaine base was generously provided by the NIDA drug supply program. All other chemicals used were reagent grade.

Animals

Sprague–Dawley albino rats were bred in our laboratory from Charles River (Wilmington, MA) stock. The animals were maintained under a 14:10

Food intake and growth

Maternal body weight data are shown in Table 1. Despite random assignment of dams to the three treatment groups, the untreated control group had a significantly lower mean body weight than the other two groups on gestational day 17 (Treatment effect: F(2,21)=5.51, P=0.012, followed by post-hoc testing). This group also showed a greater percentage increase in weight from gestational day 17 to 20 (Treatment effect: F(2,21)= 16.60, P<0.001, followed by post-hoc testing). Maternal food intake data

Discussion

To our knowledge, this is the first study to investigate the influence of maternal cocaine administration on placental monoamine transporters in rats. We found a striking up-regulation of [³H]nisoxetine-labeled norepinephrine uptake sites after just 3 days of continuous maternal cocaine treatment. There was also a smaller but statistically significant reduction in affinity of the transporter for the radioligand. These effects were specific to the placenta, as no effect was observed for fetal

Acknowledgements

This research was supported by NIDA grant DA-06495.

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¹: Present address: Laboratory of Developmental Chronobiology, Massachusetts General Hospital, 32 Fruit St., Boston, MA 02114, USA.

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Cocaine up-regulates norepinephrine transporter binding in the rat placenta

Abstract

Introduction

Section snippets

Chemicals

Animals

Food intake and growth

Discussion

Acknowledgements

Brain Res.

Anal. Biochem.

Mol. Brain Res.

Placenta

Am. J. Obstet. Gynecol.

Am. J. Obstet. Gynecol.

Trophoblast Res.

Placenta

Pharmacol. Biochem. Behav.

Brain Res.

Am. J. Obstet. Gynecol.

Placenta

Placenta

Placenta

Brain Res.