Parenchymal microvascular systems and cerebral atrophy in spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) are hypertensive, hyperactive, and hydrocephalic; furthermore SHR have smaller brain volume and weight than age-matched, normotensive Wistar-Kyoto rats (WKY). At 6-7 months of age, local cerebral glucose is sizably lower in SHR than WKY. The hypothesis that these several abnormalities of SHR lead to variations in cerebral microvascular bed morphology was tested in 6-7-month-old SHR and WKY by quantitating various parameters of small, intermediate, and large parenchymal microvessels (grouped by luminal diameter) in 21 brain areas. Within each rat strain, the microvascular bed properties such as vessel profile frequency (density) varied considerably among the 21 brain areas. In opposition to the hypothesis, mean luminal diameter as well as profile frequency, surface area, and luminal volume of the microvascular beds per unit tissue mass were virtually identical in each brain area of SHR and WKY for the three groups of microvessels. These findings coupled with the reports of less tissue per structure but similar density of neurons throughout the brain of SHR and WKY indicate that there are fewer neurons and less vascular tissue per brain structure in 6-7-month-old SHR than WKY; in addition, they suggest a linkage between the size of parenchymal microvascular beds and the surrounding nervous tissue.