Background: Hyperinsulinemia and insulin resistance are associated with left ventricular hypertrophy (LVH) and cardiovascular complications in hypertensive subjects. The aim of this study was to explore the mechanisms for LVH including activation of the renin-angiotensin system system (RAS) and the sympathetic nervous system and their activation by insulin using a rat model of hyperinsulinemia and insulin resistance.
Methods: Male Sprague-Dawley rats were fed a high-fructose or control diet. The fructose-fed rats (FFR) were divided into four subgroups that were administrated either vehicle or the following antihypertensive drugs (n = 6-8) for 4 weeks: 1) olmesartan, an angiotensin II type 1 (AT1) receptor antagonist; 2) bunazosin, an alpha1-receptor blocker; and 3) hydralazine, a direct vasodilator.
Results: Fructose feeding induced significant increases in mean systolic blood pressure (BP) levels at 4 weeks (control, 117 v fructose, 131 mm Hg), left ventricular weight, and the sum of the insulin level in response to a glucose tolerance test (2 g/kg). Fructose feeding also increased urinary excretion of epinephrine and norepinephrine, the density of cardiac alpha1-adrenergic receptors, and the content of angiotensin II in the left ventricle. All antihypertensive drugs decreased systolic BP, but only the AT1 receptor antagonist attenuated the development of LVH in FFR. The AT1 receptor antagonist did not affect glucose-mediated insulin responses, but did suppress urinary catecholamine excretion and cardiac alpha1-adrenergic receptor density.
Conclusions: Left ventricular hypertrophy in FFR may be less dependent on systemic elevations of BP and more dependent on the RAS and the sympathetic nervous system. Use of an AT1 receptor antagonist might be the most beneficial way to prevent progression of LVH through direct effects on tissue RAS and the sympathetic nervous system in FFR. As these changes occur in a rat model with hyperinsulinemia, insulin may have a role in promoting LVH by activating the local RAS and sympathetic nervous system activity.