Human ovarian receptors to human prolactin: implications in infertility

In the human, hyperprolactinemia may interfere with fertility. To find out whether or not prolactin (PRL) can act directly on human ovarian tissues, in vitro studies involving specific binding of human PRL to various human ovarian elements were carried out. Human PRL was isolated from amniotic fluid, and its intact monomeric iodinated isohormone B was prepared. Labeled PRL was incubated with plasma membranes of either granulosa or whole follicular homogenates. Relatively high specific binding sites were obtained. Saturation studies and Scatchard analysis showed a single class of binding sites with high binding affinity (Kd=1.8×108M) and a concentration of 7.9×10−15 moles/mg protein. These results clearly demonstrate the existence of specific receptors to isoprolactin B in ovarian elements with binding capacity and concentration at least equal to that found in other targets for PRL. It is reasonable to assume that hyperactivation of these receptors in states of hyperprolactinemia constitutes the cause for the disturbances in ovarian functions that lead to infertility.