Cerebral capillary bed structure of normotensive and chronically hypertensive rats

In this study cerebral capillary bed structure and the effects of chronic hypertension on these systems have been assessed in 6- to 7-month-old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Capillary diameter (D), profile frequency (Na), volume fraction (Vv), and surface area (Sv) were quantitated by light microscopic morphometry of eight brain areas including the sensorimotor cortex and subfornical organ. Previously presented data from normotensive Sprague-Dawley rats (SpD) of similar age were also compared. Within each of the three rat strains, D, Na, Vv, and Sv varied among brain areas. For the sensorimotor cortex and subfornical organ, capillary profile frequency differed significantly among the three rat strains. In SHR and WKY, there was an inverse correlation between profile frequency and diameter, i.e., as Na increased among brain areas, D decreased. In six brain areas capillary volume fraction and surface area were identical in SHR and WKY, but were lower in SpD. Consistent differences between SHR and WKY were found only for the subfornical organ, which suggests some involvement of this structure in hypertension. Since there were few statistically significant differences between SHR and WKY and many statistically significant differences between the two normotensive strains, cerebral capillary bed structure seems to be independent of arterial blood pressure in most brain areas of these rats.