Abstract
To examine the sequential localizations of procollagen Types I (Pro I) and III (Pro III) during chorioallantoic placental formation in pregnant rats, we prepared polyclonal anti-rat Pro I- and III-specific antibodies. Biochemical analysis of a fraction containing [14C]-glycine-incorporated collagen from pregnant rat uteri showed that collagen Types I and III were actively synthesized during placental development. We examined 8-, 9.5-, 13-, and 20-day gestation rat uteri immunohistochemically. At Days 8 and 9.5, in the basal decidua facing the fetal cytotrophoblastic giant cell layer and implantation site, the immunoreactivity for Pro I was higher than that for Pro III. On Day 13, the enlarged myometrium and cytotrophoblastic cell layer showed increased immunoreactivity for Pro III. Unexpectedly, polygonal trophoblastic cells invading and modifying the maternal central artery showed intense immunoreactivity for Pro III. On Day 20, the fetal mesenchyme, large fetal blood vessels, and subendothelial stroma, including fetal blood capillaries, were more immunoreactive to Pro III antibody than to Pro I antibody in the labyrinth. Pro I and III synthesis and processing appear to be developmentally regulated and may be related to control of the microenvironment for supporting the fetus, control of the maternal blood supply stabilizing the fetoplacental physiological functions, and parturition.