Arterial vasodilation and cardiovascular structural changes in normotensive rats.

Area of Science:

• Cardiovascular Physiology
• Pharmacology
• Vascular Biology

Background:

• Minoxidil, an arterial vasodilator, induces right ventricular hypertrophy (RVH) and eccentric left ventricular hypertrophy (LVH) in normotensive rats.
• The study investigates if minoxidil's effects extend to vasculature and explores underlying mechanisms.

Purpose of the Study:

• To evaluate structural alterations in cardiac and arterial tissues following minoxidil treatment.
• To examine the role of cardiac volume load and sympathetic activity in minoxidil-induced changes.
• To compare effects of minoxidil alone versus in combination with hydrochlorothiazide (HCTZ).

Main Methods:

• Long-term (35 and 70 days) administration of minoxidil or minoxidil plus HCTZ to normotensive rats.
• Assessment of cardiac weights, ventricular dimensions, and arterial medial area.
• Measurement of cardiac filling pressures, plasma and blood volumes, and norepinephrine turnover rates.

Main Results:

• Minoxidil alone increased cardiac weights, LV internal diameter, and superior mesenteric artery medial area.
• Minoxidil with HCTZ induced concentric LVH and abolished superior mesenteric artery medial hypertrophy.
• Minoxidil increased cardiac/arterial norepinephrine turnover, filling pressures, and blood volumes, effects attenuated by HCTZ during chronic treatment.

Conclusions:

• Chronic cardiac volume load influences the type of cardiac hypertrophy induced by minoxidil, possibly via cardiac sympathetic activity.
• Intravascular volume expansion or increased arterial flow drives superior mesenteric artery medial hypertrophy.
• The lack of trophic response in other arteries suggests localized mechanisms contributing to vascular adaptation.