CORTICOSTERONE IS REQUIRED FOR THE PROLACTIN RECEPTOR GENE-EXPRESSIONIN THE LATE PREGNANT MOUSE MAMMARY-GLAND

In order to clarify the prolactin receptor (PRL-R) gene expression al lactogenesis, the levels of the long and short forms of PRL-R mRNA wer e determined by the competitive RT-PCR in the pregnant, lactating and ovariectomized midpregnant mouse mammary gland. Plasma concentrations of corticosterone and progesterone were determined by RIA. The long fo rm of PRL-R mRNA level was low until 10:00 on day 18, increased 3.3-fo ld at 22:00 on day 18 of pregnancy and further increased to 4.6-fold a t 10:00 on day 0 of lactation. The short form of PRL-R mRNA level rema ined unchanged during this time period. The corticosterone:progesteron e ratio increased 15.5-fold during the last 1.5 days of pregnancy. Cor ticosterone increased the long form of PRL-R mRNA level when the tissu es on day 17 were cultured. On day 12 of pregnancy and following ovari ectomy, corticosterone was exceedingly high from 2 h to 8 h and the co rticosterone:progesterone ratio changed prior to the increase in the l ong form of PRL-R mRNA level. We conclude that corticosterone increase s the PRL-R gene expression in the mammary gland before the onset of p arturition. (C) 1997 Elsevier Science Ireland Ltd.