Dexamethasone suppresses eNOS and CAT-1 and induces oxidative stress in mouse resistance arterioles

Abstract

Long-term treatment with glucocorticoids is associated with mild to moderate hypertension. We reported previously that downregulation of endothelial NO synthase (eNOS) expression and activity is likely to contribute to this increase in blood pressure. In the present study, we tested the effects of dexamethasone on the vasodilation of microvascular arterioles using implanted dorsal skin-fold chambers in anesthetized C57BL/6J mice. Experiments were performed on control mice or on mice treated with dexamethasone (0.1-3 mg/kg of body wt). Endothelium-dependent vasodilation in response to ACh (0.1-10 microM) was reduced by dexamethasone in a dose-dependent fashion. Comparable inhibition was seen in tissues superfused with 30 microM N(G)-nitro-L-arginine methyl ester. In contrast, endothelium-independent vasodilation in response to S-nitroso-N-acetyl-D,L-penicillamine (10 microM) was not influenced by either dexamethasone or N(G)-nitro-L-arginine methyl ester. Levels of eNOS mRNA in murine hearts and NO(2)(-)/NO(3)(-) in serum were suppressed by dexamethasone (down to 63 and 50% of control values, respectively, at 3 mg/kg of body wt) along with a reduction in eNOS protein to 85.6%. Dexamethasone also concentration dependently reduced the expression of the cationic amino acid transporter-1 in murine hearts and cultured endothelial cells. The suppression by dexamethasone of the ACh-induced vasodilation could be partially reversed by dietary L-arginine (50 mg/kg of body wt) and by dietary vitamin C (10 g/kg of diet). We conclude that suppression by dexamethasone of the endothelium-mediated microvascular vasodilation involves several mechanisms including 1) downregulation of eNOS, 2) downregulation of cationic amino acid transporter-1, and 3) generation of reactive oxygen species. The demonstration that L-arginine and vitamin C can partially offset the effects of dexamethasone on microvascular arterioles suggests the potential clinical usefulness of these agents for the reduction of glucocorticoid-induced hypertension.

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

“…Since we strictly applied these criteria for what can be considered a chamber with physiological flow conditions, we eliminated 40% of the animals before the intravital microscopic studies. This number compares well to experiences made in other immunocompetent mouse species (C57BL/6, BALB/c, and ApoE KO, all showing an elimination rate of around 40%, see Li and Förstermann, 2000;Schaefer et al, 2005), but was slightly higher when compared to mice that are genetically hairless (nu/nu or nude, showing an elimination rate of around 25%; see Lehr et al, 1993). It should be acknowledged that the success rate of the chamber preparation depends largely on the quality of microsurgical technique and hence varies from experimentor to experimentor (unpublished observation), and that unexpected results are obtained in experiments in which the above described strict criteria are neglected (Schäfer et al, 2005).…”

“…We have hence asked the question whether DOCA/salt treated one-renin mice might be suitable to demonstrate a direct effect of potassium diet onendothelium-dependent vasorelaxation, in the absence of confounding anti-hypertensive effects. In order to examine the relaxation of pre-capillary resistance arterioles under conditions of an intact animal organism, we used intravital microscopy in mice chronically instrumented with a dorsal skinfold chamber (Lehr et al, 1993;Schaefer et al, 2005). We show herein that DOCA/ salt treatment attenuates endothelium-dependent vasorelaxation (in the absence of arterial hypertension) and that vasorelaxation is effectively restored in potassium-supplemented mice.…”

“…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.…”

“…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.…”