Between days 2 and 10, Ang II treatment increased systolic blood pressure in Rgs1−/−ApoE−/− mice more than in ApoE−/− mice (Fig. 5d), demonstrating that protection from aneurysm formation in Rgs1−/−ApoE−/− mice occurs despite a greater rise in blood pressure and through mechanisms that are independent of Ang II-induced hypertension. This evidence concerns the gene APOE and aneurysm.