Effect of pressurization on mechanical properties of mesenteric small arteries from spontaneously hypertensive rats.

The mechanical properties of the wall of isolated perfused arterial segments of mesenteric small arteries from 17-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY) were investigated. Third-order branches of mesenteric arteries were mounted in a pressure myograph chamber and pressurized from 1 to 140 mm Hg. Under isobaric conditions, the outer diameter and the lumen of small arteries studied were smaller in SHR than in WKY, whereas media width, media cross-sectional area and media-lumen ratio were greater in SHR. Under passive conditions, the total change in internal and external diameter in response to increasing intravascular pressure was smaller in arteries from SHR. Incremental distensibility was significantly lower in arteries of SHR at intravascular pressures between 1 and 40 mm Hg, but was significantly greater between pressures of 40-100 mm Hg. Wall stress generated by intravascular pressure was significantly smaller in arteries from SHR. As a function of wall strain (under isometric conditions), stress and incremental elastic modulus were shifted to the left in SHR vessels. Under isobaric conditions or in relation to wall stress, the slope of elastic modulus was smaller in SHR. This decrease in elastic modulus may confer additional elasticity to the vascular wall of resistance arteries from SHR. The presence of a greater distensibility at physiological levels of intravascular pressure and decreased incremental elastic modulus indicates that the changes in the structure of small mesenteric arteries in SHR can be defined as the result of a combination of eutrophic and hypertrophic remodeling.