Background: 

Although much is known about platelet function and hemostasis in adult mammalian organisms, it remains largely unclear whether hemostasis occurs in a similar fashion in the developing fetus. To investigate platelet function during fetal ontogeny, we developed a novel in vivo model in the mouse fetus allowing us to examine thrombus formation and platelet function in yolk sac vessels in murine fetuses by intravital microscopy.

Methods: 

Pregnant mice were anaesthetized, the uterus horn exteriorised and the uterus wall carefully opened, exposing the intact yolk sac and a fully functional circulation with the fetus still being attached to the placenta. Microinjection of FITC-dextran into yolk sac vessels enabled us to monitor blood flow and induce thrombus formation by phototoxic effects of the dye. We evaluated C57/bl6 fetuses of different gestational ages (E13.5, E14.5–16.5 and E17.5) for the occurrence and time course of thrombus formation (onset, firm occlusion and reflow).

Results: 

The percentage of vessels with onset as well as firm occlusion was significantly reduced in the youngest fetuses compared to older fetuses (p<0,05), while reflow occurred more often in the youngest fetuses. Furthermore, time until onset and firm occlusion was longer in E13.5 fetuses than in more mature fetuses.

Conclusion: 

We demonstrate that platelet function and the capacity to build a firm thrombus is reduced early during gestation and only improves with advancing gestational age. This observation provides the first in vivo evidence in the mouse that platelet function is developmentally regulated during fetal life.

(Supported by FöFoLe 65/10 and by SFB914)