Prolactin receptor levels on lymphocytes vary with menstrual cycle in women

Prolactin exerts effects on the immune system, potentiating T-cell growth in response to various stimuli. These effects are felt to be mediated by specific receptors present on lymphocytes for prolactin. While the presence of prolactin receptors (PRLRs) on lymphocytes is well accepted, potential fluctuations in these receptor levels in individuals have not been studied. Here we present evidence that lymphocyte prolactin levels vary throughout the menstrual cycle in females. Lymphocyte PRLR levels varied up to 10-fold as determined by radioreceptor assay on the different days of the menstrual cycle. A semi-quantitative PCR technique was used to measure message levels, and these generally correlated with radioreceptor results. We conclude that lymphocyte PRLR levels vary throughout the menstrual cycle and that these variations are due at least in part to variations in PRLR mRNA levels.