Rat decidual prolactin. Identification, molecular cloning, and characterization.

Establishment and maintenance of pregnancy require the activity of a highly specialized maternal tissue, the decidua. It is well established that the human decidua synthesizes and releases prolactin. However, in the rat, no study has been able to demonstrate the production of prolactin by the decidua. In this report, we established for the first time using Northern blot analysis and reverse transcription-polymerase chain reaction, Western blot analysis, immunocytochemistry, and enzyme-linked immunosorbent assay, that a defined cell population located in the rat antimesometrial decidua expresses prolactin mRNA, as well as synthesizes and secretes this hormone. By reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends, we cloned a full-length cDNA for rat decidua prolactin, whose sequence was identical to that of pituitary prolactin. Our results also showed that pituitary prolactin appeared to down-regulate decidual prolactin levels. Under these circumstances, inhibition of pituitary prolactin secretion led to a rise in both decidual prolactin mRNA and protein expression. Moreover, addition of exogenous prolactin to primary decidual cells in culture also caused a marked decrease in decidual prolactin mRNA expression. Finally, treatment of primary decidual cells with steroid hormones or 8-bromo-cAMP revealed a differential regulation of decidual prolactin expression from that of pituitary suggesting a tissue-specific regulation of prolactin gene expression, possibly through the use of an alternative promoter in rat decidua.