Intravital microscopy reveals endothelial dysfunction in resistance arterioles in Angiotensin II-induced hypertension

Abstract

It is known that hypertension is associated with endothelial dysfunction and that Angiotensin II (Ang II) is a key player in the pathogenesis of hypertension. We aimed to elucidate whether endothelial dysfunction is a specific feature of Ang II-mediated hypertension or a common finding of hypertension, independently of underlying etiology. We studied endothelial-dependent vasorelaxation in precapillary resistance arterioles and in various large-caliber conductance arteries in wild-type mice with Ang II-dependent hypertension (2-kidney 1-clip (2K1C) model) or Ang II-independent (volume overload) hypertension (1-kidney 1-clip model (1K1C)). Normotensive sham mice were used as controls. Aortic mechanical properties were also evaluated. Intravital microscopy of precapillary arterioles revealed a significantly impaired endothelium-dependent vasorelaxation in 2K1C mice compared with sham mice, as quantified by the ratio of acetylcholine (ACh)-induced over S-nitroso-N-acetyl-D,L-penicillamine (SNAP)-induced vasorelaxation (2K1C: 0.49±0.12 vs. sham: 0.87±0.11, P=0.018). In contrast, the ACh/SNAP ratio in volume-overload hypertension 1K1C mice was not significantly different from sham mice, indicating no specific endothelial dysfunction (1K1C: 0.77±0.27 vs. sham: 0.87±0.11, P=0.138). Mechanical aortic wall properties and endothelium-dependent vasorelaxation, assessed ex vivo in rings of large-caliber conductance (abdominal and thoracic aorta, carotid and femoral arteries), were not different between 2K1C, 1K1C and sham mice. Endothelial dysfunction is an early feature of Ang II- but not volume-overload-mediated hypertension. This occurs exclusively at the level of precapillary arterioles and not in conduit arteries. Our findings, if confirmed in clinical studies, will provide a better understanding of the pathophysiological mechanisms of hypertension.

Potassium restores vasorelaxation of resistance arterioles in non-hypertensive DOCA/salt fed mice

“…Parent and coworkers found that inhibiting NO synthesis selectively reduced acetylcholine-induced vasodilatation in cardiac resistance vessels of dogs, but failed to prevent similar responses in conductance coronary vessels (Parent et al, 1996). Recently, our group has shown, using the same mouse model as applied in the present study, that angiotensin-II-mediated hypertension (2 kidney/1 clip Goldblatt model) leads to endothelium-dependent vasodysfunction in precapillary resistance arterioles, while this effect could not be reproduced in rings of large caliber conductance vessels from the same animals ex vivo (Schaefer et al, 2012).…”

“…All data in the figures are rendered as mean ± SD. In analogy to previous publications (Schaefer et al, 2005(Schaefer et al, , 2012, endothelium-dependent (i.e. acetylcholine-induced) vasorelaxation was calculated as percent of total endothelium-independent (i.e.…”

“…This model permits the microscopic investigation of pre-and postcapillary microvessels and of nutritional capillary perfusion in a fine, striated skin muscle in non-anesthetized animals (Lehr et al, 1993;Schaefer et al, 2005Schaefer et al, , 2012. After completion of the DOCA/salt treatment, mice with a body weight of 28-32 g were anesthetized with xylazine-ketamine and titanium observation chambers were implanted into the dorsal skinfold as described previously in detail (Lehr et al, 1993).…”

“…For intravital microscopy, awake mice were placed in a Plexiglas tube fixed to a Plexiglas platform under a diagnostic microscope (Leica Dialux-20, Fig. 1) and the superfusion protocol performed as explained in detail in previous publications (Schaefer et al, 2005(Schaefer et al, , 2012. For the intravital microscopic Table 1 Mean arterial blood pressure (MAP), heart rate (HR), serum sodium and potassium levels, plasma renin activity (PRA), plasma renin concentration (PRC) and water intake in DOCA/ salt-treated one-renin gene mice.…”

“…Yet, in these studies, the capacity of potassium supplementation to preserve endothelium-dependent vasorelaxation was always accompanied by a reduction of blood pressure in treated animals, making it impossible to know whether the salutary effect of potassium on vascular function was direct or whether it was indirect, secondary to its antihypertensive action. Ex vivo studies on explanted rings of muscular arteries have not conclusively argued against this latter possibility because of the artificial ex vivo conditions and the study of large caliber conductance vessels that physiologically exert quite different functions than the precapillary resistance arterioles that are operative in blood pressure regulation (Schaefer et al, 2012).…”