Megakaryocyte-specific targeted deletion of TGF-β1 reduces platelet, platelet releasate, serum, and plasma levels of total TGF-β1 but does not affect platelet function in vitro or in vivo. (A-B) Agonist-induced platelet aggregation was similar in control and Tgfb1^flox mice. (A) Platelet-rich plasma from control and Tgfb1^flox mice was stimulated with 1μM ADP, and light transmission was measured over time (1 of 3 similar experiments is shown). (B) Washed platelets from control and Tgfb1^flox mice were stimulated with 0.125 U/mL thrombin, and the aggregation response was measured over time (1 of 3 similar experiments). (C) FeCl₃-induced carotid artery thrombosis in vivo was similar in control and Tgfb1^flox mice. Thrombosis was initiated by applying 20% FeCl₃ to the carotid arteries of control and Tgfb1^flox mice, and the time to complete cessation of blood flow was recorded as the occlusion time (n = 4). (D) Total TGF-β1 levels in platelet lysates (PLT-Lys) and platelet releasates (PLT-Rel) from control mice (n = 4) or from Tgfb1^flox (n = 4) were measured by ELISA. (D) Serum total TGF-β1 levels in control (n = 19) and Tgfb1^flox mice (n = 10) were measured by ELISA. (E) Platelet lysates from control and Tgfb1^flox mice were immunoblotted with antibodies to TGF-β1 (top panel), αIIb (middle panel), and actin (bottom panel). (F) Serum samples from 4 control and 4 Tgfb1^flox mice were immunoblotted with antibody to TGF-β1. (G) Plasma total TGF-β1 levels in control (n = 45) and Tgfb1^flox (n = 25) mice were measured by ELISA.