Prolactin enhancement of its own uptake at the choroid plexus.

The choroid plexus contains PRL receptors that function in part to transport PRL from the blood into the cerebrospinal fluid (CSF). The blood PRL concentration of female rats was altered by 1) three daily injections of haloperidol (chronic hyperprolactinemia) with or without bromocriptine administration 4 h before death, 2) bromocriptine alone for 4 h (acute hypoprolactinemia), and 3) a single vascular injection of ovine PRL (acute hyperprolactinemia). Changes in the uptake of PRL by the choroid plexus was assessed by quantitative in vivo autoradiography after the injection of radiolabeled PRL. Correlation of changes in PRL uptake at the choroid plexus with changes in PRL transport from blood to CSF was evaluated by subjecting CSF samples to sodium dodecyl sulfate-polyacrylamide gel electrophoresis after vascular injection of radiolabeled PRL. Autoradiography revealed that both chronic and acute hyperprolactinemia resulted in a significant increase in the uptake of radiolabeled PRL by the choroid plexus compared to that in untreated control animals. In contrast, bromocriptine had no effect on PRL uptake at the choroid plexus relative to that in control (untreated) animals. Chronic hyperprolactinemia, but not acute hyperprolactinemia, resulted in a significant increase in the transport of radiolabeled PRL from the blood to the CSF compared to that in untreated controls. The results are consistent with the up-regulation of PRL receptors in the choroid plexus by circulating PRL and the consequent augmentation of transport of PRL from blood to CSF.