Developmental expression and anatomical localization of endothelin-1 messenger ribonucleic acid and immunoreactivity in the rat placenta: a northern analysis and immunohistochemistry study.

Endothelin-1 (ET-1) immunoreactivity and messenger ribonucleic acid (mRNA) have previously been identified in the mammalian placenta. In the present study we examined the developmental expression of ET-1 mRNA and the localization of ET-1 mRNA and immunoreactivity within the rat placenta. Placental tissues were removed from primiparous Sprague-Dawley rats on gestational days 14, 18, and 21 and processed for blot hybridization of ET-1 mRNA and immunohistochemistry of ET-1 immunoreactive peptide. Placental tissue contained a 2.3 kb size ET-1 mRNA transcript. Placental ET-1 mRNA abundance increased approximately five-fold from day 14 to 21 of gestation (p = 0.02). To localize ET-1 mRNA within the rat placenta, day 18 placentas were dissected into the basal and labyrinth layers and processed separately for blot hybridization of ET-1 mRNA. ET-1 mRNA localized to the labyrinth zone. This was confirmed by immunohistochemical staining of day 18, 20, and 21 placental tissues with an antiserum specific to ET-1. The presence of ET-1 immunoreactivity and the stage-specific increase in ET-1 mRNA in the rat placenta suggest that ET-1 may exert paracrine effects on the placenta or uterus of the pregnant rat.