Mammary Epithelial Cells of Lactating Rats Express Prolactin Messenger Ribonucleic Acid1

Abstract

The presence of prolactin (PRL) mRNA in the mammary gland, placenta, and pituitary gland of lactating and pregnant rats was investigated by polymerase chain reaction (PCR). Polyadenylated RNA was prepared from total RNA samples by oligo(dT)-cellulose chromatography, and complementary cDNAs were synthesized. A standardized amount of cDNA from each sample was used as the template in a Taq PCR under high-stringency conditions. PCR amplified a signal with the predicted size of approximately 375 bp in mammary and pituitary glands of lactating and pregnant rats, and in placentae of pregnant rats. This band specifically hybridized with a probe overlapping the entire sequence of the mature rat (r) PRL mRNA in Southern blot analysis. When the rPRL-specific primers were used, PCR revealed no signal in the liver or in lactating mammary gland explants cultured in vitro for 48 h, while the same cDNA preparations gave strong signals for beta-actin. The viability of the mammary gland explants was also suggested by their ability to secrete immunoreactive casein in vitro. PRL mRNA was localized in the epithelium of alveoli and ducts of the lactating mammary gland by in situ hybridization. These data provide evidence that the PRL gene is expressed in the mammary gland of pregnant and lactating rats, and suggest that the mammary gland might contribute to PRL in milk by de novo synthesis. Thus, while the placenta is an exogenous source of PRL-like activities for the fetus in utero, the mammary gland might take over this function after birth.

Detection of In Situ Localization of Long Form Prolactin Receptor Messenger RNA in Lactating Rats by Biotin-Labeled Riboprobe.

“…Since MGF activity is stimulated by PRL [19], the decrease in its activity might result from the decrease in PRLRL gene transcription. The mechanism of the local reduction in PRLRL gene transcription is not known, but paracrine and autocrine [20,21] secreted PRL in milk are candidates for local regulator of PRLRL gene transcription, since PRL itself controls the expression of its own receptor [22,23]. In addition, changes in cellular morphology due to intramammary pressure could influence the transcription as suggested in the study of MGF [19].…”

The role of prolactin and growth hormone in breast cancer

“…Recently it was shown that mammary tumors and normal mammary tissue express both PRL and GH, suggesting a possible paracrine function of the hormones in tumor development and growth (Kurtz et al, 1993;Clevenger et al, 1995;. Furthermore, PRL can be secreted by breast cancer cells cultured in vitro (Ginsburg and Vonderhaar, 1995).…”

Prolactin and Angiogenesis: Biological Implications of Microheterogeneity

“…In addition to uptake of prolactin from the blood, the mammary epithelial cells of lactating animals are capable of synthesizing prolactin. The presence of prolactin mRNA (Kurtz et al 1993) as well as synthesis of immunoreactive prolactin by mammary epithelial cells of lactating rats has been described (Lkhider et al 1996). A great deal of evidence suggests that lymphocytes can be a source of prolactin as well (Gala et al 1994, Montgomery et al 1990.…”