Abstract
Prostaglandin D2 was shown to constrict the blood vessels of the isolated perfused cotyledon of the human placenta. Its potency was less than that of prostaglandin F2 alpha but similar to prostaglandin E2. As it is known to dilate uterine blood vessels it may, by its differential action on the foetal and maternal vascular beds, play a role in the local regulation of utero-placental blood flow.