CHANGES IN MESSENGER-RNA LEVELS OF A PITUITARY-SPECIFIC TRANS-ACTING FACTOR, PIT-1, AND PROLACTIN DURING THE RAT ESTROUS-CYCLE

The present study examined the changes in mRNA levels of a pituitary-s pecific trans-acting factor, Pit-1, and prolactin during the rat estro us cycle. Total cytoplasmic RNA was analyzed by Northern blot and slot -blot hybridization to examine the prolactin mRNA level. Reverse trans cription-polymerase chain reaction (RT-PCR) was performed to examine t he Pit-1 mRNA level. Proestrous and estrous prolactin mRNA levels were significantly higher than the metestrous and diestrous levels, wherea s Pit-1 mRNA levels of the estrous and metestrous stages were about tw o- to threefold higher than those of the proestrous and diestrous stag es. Proestrous Pit-1 mRNA levels increased gradually from 10.00 h to 2 0.00 h, while prolactin mRNA levels slightly decreased until 14.00 h b ut increased later until 20.00 h. During the rat estrous cycle, especi ally in the afternoon of the proestrous day, changes of prolactin mRNA levels seem to follow a prior increase of Pit-1 mRNA. Therefore, Pit- 1 may be partly involved in the regulation of prolactin gene expressio n according to the rat estrous cycle. Estradiol administration to ovar iectomized rats significantly increased both the mRNA levels of prolac tin and Pit-1, which suggests that the gene expression of Pit-1 is reg ulated by estrogen through indirect extracellular pathways.