Impaired myogenic properties of cerebral arteries from the Brown Norway rat.

Objectives: The Brown Norway rat is highly susceptible to cerebral haemorrhage when hypertension is induced experimentally, compared with the Long Evans. The aims of the study were to compare the myogenic properties and also the collagen-staining profile of the middle cerebral artery (MCA) and a small systemic artery (cremaster) from Brown Norway and Long Evans rats.

Methods: In-vitro pressure myography was used to compare the myogenic properties and the distensibility of MCA and cremaster arteries from Brown Norway rat, with those of the Long Evans rat. Histologically prepared arterial sections were stained with picrosirius red to compare the collagen-staining profile of MCA and cremaster from these strains of rat.

Results: In the presence of myogenic tone, the active pressure-diameter relationship (20-200  mmHg) was significantly different in MCA from the Brown Norway, but not cremaster arteries, compared with the Long Evans, characterized by in the lack of a myogenic range in the Brown Norway. Midwall collagen staining was significantly increased in MCA from the Brown Norway rat, compared with the Long Evans rat; this difference between rat strains was not observed in the cremaster arteries. However, the stress-strain relationship of MCA and cremaster arteries from the Brown Norway rat was shifted to the right, indicating an increased distensibilty of arteries from both vascular beds, compared with the Long Evans.

Conclusion: These data demonstrate impaired myogenic properties and differences in the collagen-staining profile of MCA but not cremaster arteries from the Brown Norway rat, compared with the Long Evans. The impaired myogenic properties of MCA from the Brown Norway rat compared with the Long Evans may explain their increased susceptibility to cerebral haemorrhage when hypertension is induced experimentally.