Decidual prolactin (prl)-releasing factor stimulates the synthesis of prl from human decidual cells

Previous studies from our laboratory demonstrated that the acute release of PRL from human decidual tissue is stimulated by a 23.5 kilodalton placental protein which we designated decidual PRL-releasing factor (PRL-RF). To determine whether PRL-RF may also affect the synthesis of PRL and/or cause a secondary increase in PRL release, we have examined the effects of purified PRL-RF on the synthesis and release of PRL over a 96-h period. Exposure of dispersed decidual cells to PRL-RF (0.5µg/nil) stimulated a biphasic increase in PRL release with acute transient stimulation during the first 0.5 h and a delayed and sustained stimulation beginning about 8 h after exposure which persisted for the duration of the 96 h. The amounts of PRL released from PRL-RF-exposed cells after 0.5, 8, 12, 24, and 96 h were 321.2 ± 36.2 (mean ± SEM, n = 3), 110.2 ± 5.3,138.2 ± 7.2± 11.2, and 201.5 ± 14.2% that of control cells. Studies of the de novo synthesis of [³⁵S]methionyl PRL indicated that the increase in PRL release after the first few hours of exposure to PRL-RF was secondary to an increase in PRL synthesis. Somatostatin (100 nM) inhibited the acute stimulatory effect of PRL-RF, but had no effect on the delayed stimulation of PRL release. On the other hand, cycloheximide (20 Î�M) completely inhibited the secondary increase in PRL release in response to PRL-RF but had no effect on the acute release. These results demonstrate that PRL-RF stimulates both the synthesis and release of decidual PRL.