[Molecular biological studies on expression of placental CRF gene and its product]

Corticotropin releasing factor, a neuropeptide secreted by the hypothalamus, was recently found to be also secreted by the placenta. However, the biological role of placental CRF is obscure. In this study, we performed Northern blots and in situ hybridizations to determine the time course and site of placental CRF production. Then we measured maternal and fetal CRF, ACTH, cortisol and DHAS levels during the course of pregnancy. The results of these studies indicated that placental CRF mRNA is 1.5 kb in size and its expression increases dramatically near term. It was shown that placental CRF is transcribed in the cytotrophoblast layer. Both maternal and fetal CRF, ACTH and cortisol increased near term. The DHAS level was significantly higher on the fetal side than in the maternal plasma. It was assumed that on the maternal side, placental CRF activates the basal level of the pituitary-adrenal axis to produce more corticosteroids. The increased corticosteroids may compete with progesterone receptors and cause the removal of a progesterone block of uterine muscle contraction. On the fetal side, placental CRF activates the pituitary-adrenal axis to produce corticosteroids and DHAS. The increased corticosteroids may again compete with progesterone receptors. The increased DHAS directly affects the uterine cervix to cause ripening of it.