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

Abstract

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 (0.5 microgram/ml) 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, 194.5 +/- 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 microM) 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.