Effect of freshly dissolved Aβ on rat penetrating arteriolar vessel tone, myogenic response and effect on ATP induced vasomotor responses. Cerebral arterioles ex vivo were treated with increasing concentrations of Aβ1-40, Aβ1-42 or reverse peptide Aβ40-1 and the effect on arteriolar tone measured. (A)Aβ1-42 constricts the arterioles similarly to Aβ1-40 at 0.1 μmol/L while at 1 μmol/L Aβ1-40 has a greater effect. * and ! denote p < 0.05 from control (ANOVA). The reverse peptide Aβ1-40 had no effect. (B) Arterioles pretreated with Aβ1-40 (0.1 μmol/L) lose myogenic response at 120 mmHg intraluminal pressure. Returning to 60 mmHg baseline pressure reestablished control tone diameter. * denotes p < 0.05 from control (n = 3 vessels). Cerebral arterioles were treated with Aβ and vasomotor responses to extraluminal ATP were observed. (C) Aβ1-40 and (D) Aβ1-42 reduce vasodilation to ATP at 1 and 100 μmol/L concentrations. In addition Aβ1-42 also enhances constriction at 100 μmol/L ATP. * denotes p < 0.05 between before and after amyloid peptide (ANOVA).