Thrombin induces the release of angiopoietin-1 from platelets

Blood platelets contain angiopoietin-1, a growth factor essential for blood vessel development via stabilization of proliferating endothelial cells. I t has recently been reported that angiopoietin-1 can act as a vascular stab ility factor (Nature Medicine 6:460, 2000). In investigating the normal tis sue distribution of angiopoietin-1 from surgically-removed frozen specimens by RT-PCR, we found it consistently present in platelets and megakaryocyte s, usually absent in relatively non-vascular tissue: breast, colon, lung, s kin, kidney, thyroid, testicle, cervix and occasionally present in tissue e nriched with vasculature: prostate, endometrium, ovary, under conditions in which mRNA stability was verified by the positive detection of internal co ntrol, actin mRNA. The consistent distribution in platelets and relatively absent distribution in non-vascular normal tissue suggested that the well-k nown role of platelets in maintaining vascular stability, may in part be du e to platelet release of angiopoietin-1 following platelet activation. In t his communication we report the incidence of Ang-l in various normal tissue s and demonstrate that thrombin-treated human platelets release angiopoieti n-1 in vitro.