Diurnal variation in cerebrospinal fluid prolactin concentration of the rhesus monkey

PRL immunoreactivity in the cerebrospinal fluid (CSF) of the rhesus monkey was found found to undergo a diurnal variation. Hourly samples of CSF from four adult male rhesus monkeys showed a mean peak PRL immunoreactivity of 6.30 +/- 2.53 ng/ml at 0200 h and a mean minimum concentration at 1500 h of 3.15 +/- .68 ng/ml. To our knowledge, this is the first report of a significant diurnal variation in the concentration of an anterior pituitary peptide hormone in CSF.