Immunoreactive Prolactin in the Cerebrospinal Fluid of Estrogen‐Treated and Lactating Rats as Determined by Push‐pull Perfusion of the Lateral Ventricles

Immunoreactive (ir) prolactin levels in the cerebrospinal fluid were measured in push‐pull perfusion samples collected from the lateral cerebral ventricles in freely‐moving ovariectomized rats prior to and after estrogen treatment, and in rats during pregnancy and lactation. Ir‐prolactin levels in cerebrospinal fluid were elevated throughout the perfusion period in ovariectomized animals given estrogen and in Day 8 lactating females following the onset of nursing by their young. Cerebrospinal fluid perfusates collected from ovariectomized animals prior to estradiol treatment and from females on Days 18 and 22 of gestation contained levels of ir‐prolactin that were below the limit of detectability of the prolactin radioimmunoassay. Data from previous studies in our laboratory suggest that pituitary prolactin is involved in the mediation of maternal responsiveness. Where and how prolactin exerts its actions in this regard remains to be determined. Results of the present study indicate that detectable levels of ir‐prolactin are present in the cerebrospinal fluid of nulliparous females after exposure to an estradiol regimen known to shorten their latency to display maternal responsiveness and in lactating females actively exhibiting maternal behavior. Once in the cerebrospinal fluid, prolactin should have access to neural target sites behind the blood‐brain barrier. The presence of ir‐prolactin in the cerebrospinal fluid of females in the present study is consistent with a role for this protein hormone, acting at the level of the central nervous system, in the facilitation of maternal responsiveness as well as in the regulation of other neural and neuroendocrine processes.