Prolactin receptor expression by splenocytes from rats in various hormonal states.

Prolactin (PRL) is mitogenic for lymphocytes in vitro, but the responsiveness of lymphocytes depends on the in vivo hormonal status of the rats from which the cells were obtained. Lymphocytes from ovariectomized (OVX) rats, but not from rats in oestrus or from male rats, respond to prolactin; administration of oestradiol to OVX rats diminishes the response. In order to determine if a correlation exists between lymphocyte responsiveness to prolactin and levels of cell surface prolactin receptors (PRL-R) expression, the percentage of splenocytes and each splenocyte subpopulation expressing surface PRL-R from rats of various hormonal states (OVX, oestradiol-injected OVX, oestrus and male) was analysed by single-colour and dual-colour flow cytometric analysis. We found that approximately 20% of splenocytes expressed surface PRL-R regardless of hormonal states (n = 16). The majority (85%) of PRL-R positive splenocytes were B lymphocytes whereas 11.1% and 4.8% of splenocytes expressing the PRL-R were CD4 positive T-helper (TH) and CD8 positive T-cytotoxic (TC) lymphocytes, respectively. B lymphocytes also stained more brightly than T lymphocytes. This distribution of PRL-R expression did not show significant alterations on total splenocytes or TH and TC lymphocytes during various hormonal stages. However, the percentage of PRL-R-positive B lymphocytes increased markedly in OVX rats (twofold), compared to rats at oestrus. In summary, no correlation was found between the responsiveness to prolactin as a mitogen and levels of PRL-R expression by lymphocytes from rats at different hormonal states. This result suggests that sex steroid hormones may control prolactin responsiveness of lymphocytes by affecting the signal transduction pathway through PRL-R rather than by altering the level of the cell surface receptor expression.

The expression of forms of prolactin receptors in splenocytes and thymocytes of neonatal rats: the effect of milk ingestion.

Because prolactin (PRL) plays a role in neonatal immune development, we examined the expression of prolactin receptors (PRL-R) in neonatal lymphoid tissues. We had shown previously that deprivation of milk-borne PRL, days 2-5 in the neonatal rat, leads to enhanced in vitro mitogenesis of thymocytes and splenocytes as well as a change in lymphoid-specific, cell surface antigens (GROVE et al. 1991). In this present study, we asked if neonatal lymphocytes express PRL-R; which forms of PRL-R are expressed (long vs. short form); when these forms are expressed during development; and if milk ingestion plays a role in receptor expression. Two approaches were taken using neonatal rat thymocytes and splenocytes: RNA was analyzed by polymerase chain reaction (PCR) and cells were stained with antibody to PRL-R and analyzed by flow cytometry. In regard to cell surface expression, the percentage of PRL-R positive splenocytes was greater than thymocytes at all ages tested. In the spleen, the percentage of PRL-R positive cells gradually increased to adult levels by day 10; in the thymus the percentage fell to adult levels by the first day after birth. Finally, milk ingestion in the first 7 h decreased the percentage of cells expressing cell surface PRL-R. Tissues from animals deprived of milk during this time expressed PRL-R at the same level as the newborn.