Angiotensin II promotes intramural hematoma of aorta in juvenile mice at early stage

Intramural hematoma (IMH) is a serious aortic condition characterized by the presence of a contained hematoma within the aortic media. However, the animal model with a high incidence of IMH was lacking, and the specific pathological characteristics of IMH have not been thoroughly characterized. We conducted an experimental study using 4-week-old male, 4-week-old female, and 8-week-old male C57BL/6J mice. These mice were subjected to angiotensin II infusion at a rate of 1000 ng/kg/min for a period of 4 days. In situ imaging was performed, and aorta was harvested and serially sectioned. Histological staining and immunostaining techniques were employed, and the subcellular structure was examined using transmission electron microscopy. Our findings revealed that 4-week-old male mice exhibited a higher susceptibility to angiotensin II-induced IMH, characterized by more circumferential appearances and larger affected areas. Furthermore, IMH was more likely to occur in the upper segment of the descending aorta rather than the lower segment. Within the IMH, older fibrinous thrombus was predominantly observed near the adventitia, while younger red thrombus was more prevalent near the lumen. Additionally, platelet activation and degranulation were observed, along with fibrin cross-linking and thrombus organization, indicating a potential relationship between platelet activation and the progression of IMH. Our study demonstrated that angiotensin II infusion promoted the development of IMH during the early stages, especially in juvenile mice. Furthermore, the presence of platelet activation and thrombus organization suggested their potential involvement in the progression of IMH.