ISOLATION OF MEGAKARYOCYTES FROM HUMAN PLACENTAE

Shedding of cytoplasm from circulating megakaryocytes (MKs) within the pulmonary vasculature suggests the lungs are an important site for no rmal platelet production. Fetal lungs receive only a minor fraction of the circulating blood volume. The placenta may act as a site for intr auterine platelet formation. Isolation of MKs from fetal vessels withi n the placenta has not been previously reported. Immediately after del ivery, 3 human placentae were subjected to forward and retrograde perf usion across the placental capillary bed on the fetal side. MKs in per fusates were harvested by 'whole blood filtration' and identified by m orphological and immunochemical methods. All perfusates yielded MKs. Q ualitatively MKs with copious cytoplasm were more commonly found in pe rfusates collected from fetal arteries compared with those from fetal veins. This is consistent with filtration of MKs and fragmentation of their cytoplasm within the placental microcirculation to produce plate lets. Perfusion of human placentae followed by filtration of perfusate s is a useful technique for harvesting fetal MKs and permitting furthe r elucidation of their physiological role.