Structural and functional properties of isolated, pressurized, mesenteric resistance arteries from a vasopressin-deficient rat model of genetic hypertension.

In this study we examined the structural and functional properties of mesenteric resistance arteries isolated from normotensive and hypertensive vasopressin-deficient rats. Hypertensive rats had a significantly higher mean arterial pressure (176 +/- 3 mm Hg) than normotensive controls (121 +/- 2 mm Hg). First- and second-order mesenteric resistance arteries were set up in a pressure myograph and pressurized to the mean arterial pressure of the rat from which they had been isolated. Vessels were fixed with glutaraldehyde, embedded in Araldite, sectioned, and examined histologically. First- and second-order mesenteric resistance arteries from hypertensive rats displayed a reduced internal diameter and increased media-to-lumen ratio compared with their normotensive controls. However, there was no evidence for an increased media content, indicating that the reduced internal diameter of hypertensive arteries was consequent to either remodeling of similar amounts of wall material or a reduced artery distensibility but not vascular growth. Pressurized arteries were also examined with respect to their responsiveness to the vasoconstrictors norepinephrine and arginine vasopressin and to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator papaverine. Both first- and second-order mesenteric arteries from hypertensive rats displayed enhanced sensitivity to norepinephrine compared with their normotensive controls. This effect was specific for norepinephrine, because responses to arginine vasopressin were similar in vessels isolated from normotensive and hypertensive rats. No evidence was found for an impaired endothelium-dependent vasodilatation in arteries from hypertensive rats. Indeed, in hypertensive vasopressin-deficient rats responses to acetylcholine were increased in first-order arteries compared with those from normotensive rats. Responses to papaverine were similar in arteries isolated from either normotensive or hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)