The influence of antihypertensive treatment on the renal arterial structure in spontaneously hypertensive rats. A morphometric study.

Spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP) were treated with a combination of a beta 1-blocker (metoprolol) and a Ca++-antagonist (felodipine) from 1 to 4 months or 4 to 6 months of age. The renal arterial trunks as well as more distal parts of the renal arterial bed were fixed by immersion and embedded in plastic. The media cross-sectional area and the length of the internal elastic membrane were measured on cross-sectioned arteries. The media thickness, luminal radius and the ratio between media thickness and luminal radius (m/r ratio) were then calculated for a standardized condition, assuming a smooth and circular internal elastic membrane, in which the arteries were compared. The m/r ratio was markedly reduced in the most proximal as well as in more distal arterial segments of the treated animals when compared with untreated rats of corresponding age and category. The quotient was somewhat reduced also when compared with normotensive controls (WKY) although the systolic blood pressure in younger treated rats was not fully normalized. The results may suggest that the present treatment influences the arterial walls not only by reducing the pressure load but also through pressure-independent mechanisms.