Placenta is a unique organ where all substances that are essential for the developing fetus are transported from maternal to fetal circulation. Since fetus needs a large amount of oxygen for its growth, enough amount of heme, which is essentially involved in the transport of oxygen and electrons, should be required in placenta. However, heme metabolism in placenta remained unclear. Here we report rat placental mRNA expressions of 6aminolevulinate synthase (ALAS) and heme oxygenase (HO), rate-limiting enzymes of heme synthesis and degradation, respectively. ALAS mRNA level increased during pregnancy and reached maximal level, about 1.5 times of that in adult liver, on day 20 of gestation. Immunohistc, chemical study demonstrated that expression of ALAS was restricted to syncytiotrophoblast. On the other hand, HO mRNA level in placenta was the highest among feto-placental tissues. The maximal level of HO mRNA was on day 15 of gestation, showed as high as 20 times of that in adult liver (equivalent to adult splenial level), then decreased toward the day of birth. HO protein was also distributed in syncytiotrophoblast, demonstrating one of the major sites of heme metabolism in fetus. Maternal uterine vessel ligation on day 19 of gestation resulted in transient increase of ALAS mRNA and decrease of HO mRNA. These findings indicate that placental syncytiotrophoblast is one of the main tissues of heme metabolism, which is regulated by the status of oxygen supply from mother and requirement of fetus.
|Publication status||Published - 1997|
ASJC Scopus subject areas
- Molecular Biology