Opposite Effects of Arterial Vasodilators on Cardiac vs. Arterial Hypertrophy and Sympathetic Activity in Spontaneously Hypertensive Rats

To investigate whether cardiac and arterial structure and sympathetic activity changes in a similar fashion during chronic arterial vasodilation, we evaluated the morphology and sympathetic activity of the mesenteric arterial bed and the left (LV) and right (RV) ventricles of 16-week-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs) after 35 and 70 days of treatment with the arterial vasodilator minoxidil. The minoxidil-induced antihypertensive response was associated with an increase in ventricular sympathetic activity, potentiation of RV hypertrophy (RVH), and the development of eccentric LV hypertrophy (LVH). In the mesenteric arterial bed, minoxidil decreased the sympathetic activity, increased the lumen of the superior mesenteric artery, and decreased the medial area of the large and small mesenteric arteries. We conclude that the contrasting effects of minoxidil on cardiac vs. arterial structure may--in part--relate to selective effects on regional sympathetic activity.