LACTATION INCREASES PROLACTIN RECEPTOR EXPRESSION IN SPLEEN AND THYMUS OF RATS

Prolactin receptors (PRL-R) are widely expressed on cells of the immun e system. During lactation, the increase in serum PRL levels may modif y the gene expression of these receptors. Specific PRL binding sites a nd the expressions of both PRL-R-L and PRL-R-S forms in thymus and spl een of nulliparous control, 10-day postpartum lactating, and 10-day po stpartum nonlactating rats were studied. A semi-quantitative RT-PCR te chnique was used to detect the PRL-R gene transcript in the tissues. O ur results showed that specific PRL binding sites and PRL-R-L mRNA and PRL-R-S mRNA were present in the lymphoid tissues with the PRL-R-L mR NA predominant. Lactation markedly increased specific binding sites an d PRL-R-L mRNA in both spleen and thymus and only PRL-R-S in spleen. N o differences between nulliparous control and postpartum nonlactating rats were observed in any of the parameters measured. The parallel inc rease in specific PRL binding sites and PRL-R-L mRNA suggests that lac tation up-regulates PRL-R expression in lymphoid tissues and may be be neficial to the maternal immune system.