Morphology and function of mesenteric resistance arteries in transgenic rats with low-renin hypertension

The renin-angiotensin system plays an important role in blood pressure control. Recently the mouse Ren-2 renin gene was introduced into the genome of rats, producing low-renin hypertensive animals. The aim of the present study was to characterize the pharmacological and morphological properties of mesenteric resistance arteries from transgenic rats.

Segments of small arteries were taken from the mesenteric bed of 13-week-old transgenic rats and from age-matched Sprague-Dawley controls.

Vessels were mounted on an isometric myograph permitting direct measurements of vessel isometric wall tension. Vessel morphology was measured with a microscope using a water-immersion objective.

The transgenic versus Sprague-Dawley rat comparison is similar to that seen previously for spontaneous hypertensive rats (SHR) versus Wistar-Kyoto (WKY) rats as regards active effective pressure (increased), lumen diameter (decreased) and media thickness (increased). However, in contrast to SHR vessels, where media cross-sectional area has previously been shown to be increased compared with WKY vessels, vessels from transgenic rats had the same media cross-sectional area as those from Sprague-Dawley rats. There was neither cellular hypertrophy nor hyperplasia. However, an increased number of smooth muscle layers was found, indicating a rearrangement of existing material.

Although the structural changes found in transgenic rats may account for the increased pressure response, hypertension in this animal is apparently not caused by general vascular growth.