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.