Structure of Cerebral Arterioles in Mice Deficient in Expression of the Gene for Endothelial Nitric Oxide Synthase

Abstract

Abstract-We examined effects of pharmacological inhibition of nitric oxide synthase (NOS) and genetic deficiency of the endothelial isoform of NOS (eNOS) on structure and mechanics of cerebral arterioles. We measured pressure, diameter, and cross-sectional area (CSA) of the vessel wall (histologically) in maximally dilated cerebral arterioles in mice that were untreated or treated for 3 months with the NOS inhibitor, N G -nitro-L-arginine methyl ester (L-NAME; 10 mg/kg per day in drinking water). Treatment with L-NAME increased systemic arterial mean pressure (SAP; 143Ϯ4 versus 121Ϯ4 mm Hg, PϽ0.05) and CSA (437Ϯ27 versus 310Ϯ34 m 2 , PϽ0.05). These findings suggest that hypertension induced in mice by NOS inhibition is accompanied by hypertrophy of cerebral arterioles. To determine the role of the eNOS isoform in regulation of cerebral vascular growth, we examined mice with targeted disruption of one (heterozygous) or both (homozygous) 2 ) eNOS-deficient mice. Carotid ligation normalized cerebral arteriolar pulse pressure did not prevent increases in CSA in homozygous eNOS-deficient mice. Thus, cerebral arterioles undergo hypertrophy in homozygous eNOS-deficient mice, even in the absence of increases in arteriolar pulse pressure. These findings suggest that eNOS plays a major role in regulation of cerebral vascular growth. Key Words: hypertension Ⅲ L-NAME Ⅲ endothelial nitric oxide synthase deficiency Ⅲ vascular hypertrophy S mall resistance arteries and arterioles undergo hypertrophy in several models of chronic hypertension. 1-3 Several determinants apparently contribute to vascular hypertrophy, including increases in arterial pressure, 4 particularly pulse pressure, 5-7 sympathetic nerves, 8,9 genetic factors, 3 the reninangiotensin system, 10,11 and the endothelium-derived contracting factor, endothelin. 12 Another determinant that may contribute to vascular hypertrophy during chronic hypertension is nitric oxide (NO). This suggestion is based on the following observations. First, it has been observed that vasodilator drugs that generate NO inhibit mitogenesis and proliferation of vascular muscle in culture. 13 Second, we have found that hypertension induced in rats with the nitric oxide synthase (NOS) inhibitor, N G -nitro-L-arginine methyl ester (L-NAME), produced hypertrophy of cerebral arterioles, even when increases in cerebral arteriolar pulse pressure were attenuated with unilateral carotid ligation. 14 These observations suggest that in addition to regulation of resting vascular resistance, NO may play an important role in regulation of vascular structure.A major limitation of using NOS inhibitors to study the role of NO in cerebral vascular hypertrophy is that most of these agents nonselectively inhibit all isoforms of NOS.

Endothelial dysfunction and arterial pressure regulation during early diabetes in mice: roles for nitric oxide and endothelium-derived hyperpolarizing factor

“…Consistent with our present findings, Chatziantoniou et al (7) found that in mice, chronic L-NAME treatment produced a gradual increase in arterial pressure (measured by tail cuff) over a period of 14 wk. Other studies have also demonstrated pressor responses to L-NAME, administered via the drinking water, of comparable magnitude to that which we observed in the present study (2,29,30,32). The fact that MAP was lower in mice treated chronically with L-NAME than in eNOS Ϫ/Ϫ mice may reflect incomplete blockade of NOS by this oral L-NAME treatment.…”

“…Concentration response curves to acetylcholine (ACh) were evaluated in small mesenteric arteries taken from C57BL/6J mice following treatment with either vehicle (A; n ϭ 4 -5), L-NAME, (B; 100 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 for 5 wk; n ϭ 4), STZ (C; 200 mg/kg single dose 7 days prior to the experiment; n ϭ 4 -6) or L-NAME ϩ STZ (D; n ϭ 4). In groups (A-D) responses were obtained under control conditions and in the presence of indomethacin (Indo; 3 M); Indo (3 M) ϩ L-NAME (100 M), and 1H- [1,2,4]oxadiazolo [4,3-a]quinoxaline-1-one (ODQ; 10 M); Indo (3 M) ϩ charybdotoxin (Chtx; 50 nM) and apamin (100 nM); and indomethacin (3 M) in combination with L-NAME (100 M), ODQ (10 M), Chtx (50 nM), and apamin (100 nM). Note that in Fig.…”

Chronic renal failure alters endothelial function in cerebral circulation in mice

“…Body temperature was maintained at ϳ37°C with a heating pad. Arteriolar pressure and diameter on the cerebrum were measured as described previously (3).…”

Activation of Transient Receptor Potential Vanilloid 1 by Dietary Capsaicin Delays the Onset of Stroke in Stroke-Prone Spontaneously Hypertensive Rats

“…Baumbach et al reported that inhibition of eNOS using N G -nitro-L-arginine methyl ester resulted in hypertrophy of cerebral arterioles of mice. 5 Furthermore, eNOS-deficient mice developed hypertrophy of cerebral arterioles, which was independent of increasing arterial pulse pressure. 5 Although diet may influence stroke risk, the optimal dietary habits for stroke prevention are not well established.…”

“…2,3 eNOS-deficient mice exhibit larger cerebral infarctions after middle cerebral artery occlusion, 4 and cerebral arterioles undergo hypertrophy. 5 Further inhibition of eNOS activity reduces cerebral blood flow and increases the size of cerebral infarct in animals. 4 Genetic variation at the eNOS locus represents a genetic risk factor for increased susceptibility to human ischemic stroke.…”