PRL and Increased circulating prolactin concentration: On the other hand, the possible influence of prolactin on the development of infertility in endometriosis patients is not only the influence of systemic elevated prolactin levels or occult hyperprolactinaemia, but rather on the local level, as local prolactin acts as a cytokine, mitogen, and immunomodulator, and endometriotic tissue is susceptible to such actions.