Although the primary emphasis of research on spontaneously hypertensive rats (SHR) tends to be on adult animals, the young SHR can have a mean arterial pressure that is elevated above normal almost proportionately as much as in adult SHR. This study attempted to determine whether the cerebral vasculature of 4- to 5-week-old SHR used existing normal mechanisms to tolerate hypertension or had microvascular characteristics uniquely suited for hypertensive life. At mean arterial pressures above about 60 mm Hg, the arterioles of SHR were constricted compared with similar branch order vessels of normal Wistar-Kyoto rats (WKY). At arterial pressures below 60 mm Hg, however, the inner diameters of arterioles in normal and hypertensive rats can be similar. At arterial pressures of 40 to 120 mm Hg, normal WKY maintained blood flow within ± 10 of that at the resting arterial pressure of 90 mm Hg; SHR with a mean arterial pressure of 120 mm Hg regulated blood flow over a pressure range of 60 to 160 mm Hg. Normal WKY had petechial hemorrhages from venules and sustained loss of arteriolar tone at arterial pressures above 120 mm Hg, which is the resting arterial pressure of 4- to 5-week-old SHR. Microvascular pressure measurements indicated that the resistance of cerebral arteries was increased, because they dissipated about 50% of the arterial pressure in SHR compared with about 40% in WKY. Pressures in the smallest venules of WKY and SHR (12.7 ± 1 vs 10.6 ± 1 mm Hg) were similar, and presumably, capillary pressures were protected from hypertension in SHR. The overall data indicated that at as early as 4 to 5 weeks of age normal cerebral vascular regulatory mechanisms are incapable of protecting the microvasculature from hypertension and mechanisms to enhance vasoconstriction are an essential requirement in the developmental stage of hypertension.
ASJC Scopus subject areas
- Internal Medicine