Aggregatory characteristics and expression of the collagen adhesion receptor in fetal porcine platelets.

Fetal wound healing differs significantly from that of the adult by its rapidity, the paucity of an inflammatory response, and the lack of scarring. In the adult, activation and aggregation of platelets at the site of injury result in the release of cytokines and inflammatory mediators that stimulate wound healing by initiating an acute inflammatory response. The aim of this study was to characterize the activity of midtrimester (day 60) and third-trimester (day 95) fetal porcine platelets (full term, 114 days) compared with that of adults in an attempt to understand the lack of inflammation in fetal wounds. The aggregatory capabilities of adult and fetal platelets were analyzed after exposure to adenosine diphosphate (ADP) concentrations of 10 mumol/L and 40 mumol/L concentrations, collagen of 0.19 mg/mL, and arachidonic acid of 0.5 mg/mL. Expression of the alpha 2 subunit of the collagen receptor (alpha 2 beta 1) was evaluated by Western blot analysis. The aggregation of day-60 fetal platelets when exposed to ADP (10 mumol/L and 40mumol/L) and collagen was significantly lower than that of the adult. The aggregation of third-trimester platelets to 10 mumol/L of ADP was similar to that of the adult and significantly greater than that of midtrimester fetuses at higher concentrations (40 mumol/L). Both fetal groups responded suboptimally to collagen, and the response was significantly less than that of adults. In contrast, arachidonic acid caused rapid and complete aggregation of both fetal platelet groups, suggesting that both mid- and late-trimester fetal platelets possessed the ability to fully aggregate with the appropriate stimulus. The different aggregatory responses to collagen could not be explained by differences in collagen receptor expression, because these were found to be similar in adults and midtrimester fetuses. It is concluded that although fetal platelets have the potential to aggregate effectively, they aggregate poorly to collagen and exhibit improved aggregation to ADP with increasing maturity. There is a transition to "adultlike" platelet aggregatory activity in the third trimester, which correlates with the period of transition to adultlike wound healing in utero. Similar expression of the alpha 2 beta 1 collagen receptor in the fetus and adult cannot explain the differences observed in their responses to collagen.