Differential Alteration in Vascular Structure of Resistance Arteries Isolated From the Cerebral and Mesenteric Vascular Beds of Transgenic [(m Ren-2 )27], Hypertensive Rats

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Abstract
In this study we examined the structural properties of cerebral and mesenteric resistance arteries isolated from normotensive, Sprague-Dawley (SD) rats (mean arterial pressure [MAP], 110±3 mm Hg) and hypertensive, transgenic (TG) rats (MAP, 167±4 mm Hg), which express the mouse Ren-2 renin gene. Vessels were set up in a pressure myograph, and ID and vascular wall thickness were determined at increasing intraluminal pressures. Arteries were subsequently pressurized to the MAP of the animal from which they were isolated and were fixed with glutaraldehyde before being embedded in araldite, sectioned, and examined histologically. The middle cerebral artery (MCA) isolated from SD rats and TG rats had similar media cross-sectional areas. There was no difference in MCA diameter at 10 mm Hg in vessels from TG rats compared with SD rats. However, at higher distending pressures, the diameter of the MCA from TG rats was significantly smaller than that of vessels from SD rats. This reduced ID at the higher pressures was a consequence of a decreased distensibility of the MCA from TG rats (as shown by a leftward shift of the stress-strain relationship in arteries from TG rats) and was not caused by an increase in wall thickness. First- and second-order mesenteric resistance arteries isolated from TG rats displayed an increased wall thickness and media content compared with vessels from SD rats. However, this alteration in mesenteric artery structure did not impinge on the ID of arteries from TG rats; there was no difference in the IDs of mesenteric resistance arteries between the two strains at any distending pressure. These observations show that there are distinct regional alterations in vascular structure in hypertensive TG rats expressing the mouse Ren-2 renin gene. Mesenteric resistance arteries isolated from TG rats display signs of vascular growth, although this structural alteration does not produce a reduction in the ID of these arteries per se. In contrast, cerebral arteries from TG rats do not show increased growth but have a reduced vascular distensibility, which results in a smaller ID compared with vessels from SD rats.