Expression of Prolactin Gene in Spontaneous Mammary Tumors in Aging Fischer 344 Rats

Expression of extra pituitary prolactin (PRL) has been recently reported in the mammary gland. However, spontaneous mammary tumors occurring in aging rats have not been investigated for PRL production. The present study was undertaken to examine the expression of PRL gene in rat mammary tumors spontaneously arisen in rats with pituitary prolactinomas among 130 female Fischer-344 (F-344) rats. The tumors examined were fibroadenoma (adenomatous type) in the 18-month old rat and adenocarcinoma (alveolar/tubular type) in the 21-month old rat. PRL mRNA was examined by solution and in situ reverse transcription-polymerase chain reaction (RT-PCR) method. The predicted amplified products for PRL mRNA were identified in both tumors, and its expression was confirmed to be in the cytoplasm of epithelial cells. The results of the present study showed that PRL gene is expressed in spontaneously arising mammary tumors.