Evidence of prolactin receptors in the choroid plexus and a possible role in water balance in neonatal brain.

Tissue dehydration, including that of the brain, is a natural part of maturation. In the newborn it is accompanied by an acute salt water diuresis which is particularly pronounced in the premature infant. The decrease in cranial volume and fall in intracranial pressure to subatmospheric levels observed in premature infants after birth suggests that the brain shares in this process. Since fluid homeostasis is normally under hormonal control, the inordinate loss of fluid in the prematurely born may be attributable to a hormonal imbalance. The possibility that prolactin, a proven osmoregulatory hormone in submammalian species but not in mammals and primates, may have an important role in this process is suggested by recent evidence that prolactin regulates tissue water in fetal and newborn animals. If this hormone assists in the regulation of water and electrolyte content of the brain during the perinatal period then prolactin receptors might be expected at blood-brain and blood-CSF barriers. Our study with preterm, term and adult rabbits indicates that prolactin receptors are present and in much higher concentrations in the choroid plexus than in other tissues examined. Specific binding of prolactin to receptors on tissues normally is observed to increase with age. Since binding to the choroid plexus decreased with age it would suggest that the effect of prolactin on choroid plexus function may be more important during the perinatal than later stages of development.