THE REGULATION OF THE PROLACTIN RECEPTOR GENE-EXPRESSION IN THE MAMMARY-GLAND OF EARLY PREGNANT MOUSE

The purpose of this research was to examine the hormonal regulation of the PRL receptor (PRL-R) gene expression in the mammary gland of earl y pregnant mouse. Following reverse-transcription, the quantity of PRL -R mRNA was determined by the competitive polymerase chain reaction. T he level of long form PRL-R (PRL-R(L)) mRNA changed cyclically with th e highest at estrus and the lowest at diestrus II. PRL-R(L) mRNA was m aintained at high levels for the first 3 days of pregnancy but decline d to lower levels on day 5. Mice ovariectomized on day 2 of pregnancy maintained the same level of PRL-R(L) mRNA during the 24 h-period. The level of PRL-R mRNA increased more than 2- and 2.7-fold with 17 beta- estradiol and PRL, respectively, and the progesterone concentration de creased its levels to 71% of the vehicle-injected control. The increas ing action with 17 beta-estradiol and PRL was suppressed by administra tion of progesterone. Mice ovariectomized on day 3 had a 1.8-fold high er level than that of the sham-operated control. The short form of PRL -R remained at low levels throughout the experiments. The results sugg ested that the expression of the PRL-R gene was suppressed when serum progesterone increased during early pregnancy.