Prolactin Receptor Gene Expression in Rat Mammary Gland and Liver during Pregnancy and Lactation

Abstract

The expression of two forms of PRL receptor messenger RNA was measured at different stages of pregnancy and lactation in mammary gland and liver from Sprague-Dawley rats, using 32P-labeled complementary DNA probes encoding the extracellular part of the receptor (E probe), common to the two forms and a probe encoding the intracellular part of the long form of the receptor (I probe), that only recognizes sequences specific to the long form of the receptor. Hybridizations were performed in Northern blots obtained from electrophoreses of poly (A+) enriched RNA preparations from mammary glands and livers of rats on days 0, 6, 12, 19, and 21 of pregnancy and 5, 10, 15, and 20 of lactation. The Northern blots were also hybridized with a chicken beta-actin probe, to correct for the amount of mRNA added and the different metabolic states of the tissues. Both tissues expressed the same forms of PRL receptor mRNAs, namely bands at 2.5, 3, and 5.5 kilobases encoding the long form of the receptor and a major band at 1.8 kilobases encoding the short form. The liver expressed all the receptor mRNA forms in much higher quantity than the mammary gland, independent of the reproductive state. In liver there was an increase of all the transcripts on day 19 of pregnancy, followed by an abrupt decline at the onset of lactation, to levels lower than those of virgin rats. In contrast, mammary gland PRL receptor mRNAs were low in virgin and pregnant animals, increased significantly at day 21 of pregnancy, and continued to increase throughout lactation. Treatment of day 19 pregnant rats with the antiprogesterone RU 486 induced, 24 h later, PRL receptor mRNAs in mammary gland but not in liver. There were no significant differences in the relative proportions of long to short forms of PRL receptor mRNAs at the different reproductive states, but the proportion of the long form was slightly greater in mammary gland than in liver. Membrane PRL receptor concentrations were also measured in the same tissues used for the mRNA study by binding to a 125I-labeled monoclonal antibody (U5), which specifically recognizes the PRL receptor at a site different from the hormone binding site. The quantity of receptor measured by U5 binding was approximately 3 times higher than that measured with 125I-labeled ovine PRL.(ABSTRACT TRUNCATED AT 400 WORDS)

Milk Protein Synthesis in the Lactating Mammary Gland: Insights from Transcriptomics Analyses

“…For instance in rats, prolactin concentration in plasma increases significantly just before parturition and remains high for the entire lactation [110], accompanied also by a concomitant increase in prolactin receptor [111] which appears similar to the pattern of prolactin receptor in mouse mammary during lactation [112]. In contrast, prolactin concentration in dairy cows increases dramatically at the onset of lactation and decreases afterwards to levels observed prior parturition, and prolactin receptor expression does not increase [4].…”

The role of prolactin and growth hormone in breast cancer

“…Both GHR (Mertani et al, 1998) and PRLR (Jahn et al, 1991) are expressed in the mammary gland. The respective activity of GH on the GHR and the PRLR diers related to what species the GH is derived from.…”

Acute Expression of the PRL Receptor Gene after Ovariectomy in Midpregnant Mouse Mammary Gland.

“…It has been reported that PRL-RL mRNA is dominant in the mammary glands of lactating mice [27], rabbits [28] and rats [29], but the dominant PRL-R mRNA species is for PRL-Rs mRNA in the mouse [19] and rat liver [30]. Although three PRL-Rs mRNA species are reported in the mouse ovary [23], 5'-and 3'-primers used here are able to anneal with these PRL-Rs cDNAs and to be used for amplification in PCR.…”