PROLACTIN RECEPTOR EXPRESSION BY SPLENOCYTES FROM RATS IN VARIOUS HORMONAL STATES

Prolactin (PRL) is mitogenic for lymphocytes in vitro, but the respons iveness of lymphocytes depends on the in vivo hormonal status of the r ats from which the cells were obtained. Lymphocytes from ovariectomize d (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 lympho cyte responsiveness to prolactin and levels of cell surface prolactin receptors (PRL-R) expression, the percentage of splenocytes and each s plenocyte subpopulation expressing surface PRL-R from rats of various hormonal states (OVX, oestradiol-injected OVX, oestrus and male) was a nalysed by single-colour and dual-colour flow cytometric analysis. We found that approximately 20% of splenocytes expressed surface PRL-R re gardless of hormonal states (n=16). The majority (85%) of PRL-R positi ve splenocytes were B lymphocytes whereas 11.1% and 4.8% of splenocyte s expressing the PRL-R were CD4 positive T-helper (T-H) and CD8 positi ve T-cytotoxic (T-C) lymphocytes, respectively. B lymphocytes also sta ined more brightly than T lymphocytes. This distribution of PRL-R expr ession did not show significant alterations on total splenocytes or T- H and T-C lymphocytes during various hormonal stages. However, the per centage of PRL-R-positive B lymphocytes increased markedly in OVX rats (twofold), compared to rats at oestrus. In summary, no correlation wa s found between the responsiveness to prolactin as a mitogen and level s of PRL-R expression by lymphocytes from rats at different hormonal s tates. This result suggests that sex steroid hormones may control prol actin responsiveness of lymphocytes by affecting the signal transducti on pathway through PRL-R rather than by altering the level of the cell surface receptor expression.