Prostaglandins and the maternal placental circulation: review and perspectives.

The objective of this article is to present an evaluation of the problems encountered in assessing the effects of prostaglandins (PGs) on the uteroplacental vasculature and circulation as well as to review pertinent experimental data. Problems in the measurement of uteroplacental blood flow are mainly due to biologic differences between placentation in different species. The physiologic role of PGs in the modulation and regulation of uterine and placental blood flows is difficult to investigate because PGs are local hormones. In addition, the direct effects of PGs on the uteroplacental circulation cannot be easily distinguished from the indirect effects due to myometrial contractions and interactions with other vasoactive substances. There is some experimental evidence that the dilation of the uteroplacental vasculature during pregnancy could be a result of the physiologic balance of local vasodilator PGs produced in the uterine vessels and vasoconstrictor effects of circulating vasoactive substances. The role of prostacyclin as well as that of platelet-thromboxane A2 in the physiologic regulation of uteroplacental blood flow remains to be elucidated, in particular in primates.