Chronic treatment with vitamin D lowers arterial blood pressure and reduces endothelium-dependent contractions in the aorta of the spontaneously hypertensive rat

Beneficial effects of calcitriol on hypertension, glucose intolerance, impairment of endothelium-dependent vascular relaxation, and visceral adiposity in fructose-fed hypertensive rats

Besides regulating calcium homeostasis, the effects of vitamin D on vascular tone and metabolic disturbances remain scarce in the literature despite an increase intake with high-fructose corn syrup worldwide. We investigated the effects of calcitriol, an active form of vitamin D, on vascular relaxation, glucose tolerance, and visceral fat pads in fructose-fed rats. Male Wistar-Kyoto rats were divided into 4 groups (n = 6 per group). Group Con: standard chow diet for 8 weeks; Group Fru: high-fructose diet (60% fructose) for 8 weeks; Group Fru-HVD: high-fructose diet as Group Fru, high-dose calcitriol treatment (20 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding; and Group Fru-LVD: high-fructose diet as Group Fru, low-dose calcitriol treatment (10 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding. Systolic blood pressure was measured twice a week by the tail-cuff method. Blood was examined for serum ionized calcium, phosphate, creatinine, glucose, triglycerides, and total cholesterol. Intra-peritoneal glucose intolerance test, aortic vascular reactivity, the weight of visceral fat pads, adipose size, and adipose angiotensin II levels were analyzed at the end of the study. The results showed that the fructose-fed rats significantly developed hypertension, impaired glucose tolerance, heavier weight and larger adipose size of visceral fat pads, and raised adipose angiotensin II expressions compared with the control rats. High- and low-dose calcitriol reduced modestly systolic blood pressure, increased endothelium-dependent aortic relaxation, ameliorated glucose intolerance, reduced the weight and adipose size of visceral fat pads, and lowered adipose angiotensin II expressions in the fructose-fed rats. However, high-dose calcitriol treatment mildly increased serum ionized calcium levels (1.44 ± 0.05 mmol/L). These results suggest a protective role of calcitriol treatment on endothelial function, glucose tolerance, and visceral adiposity in fructose-fed rats.

Potential of vitamin D in treating diabetic cardiomyopathy

Cardiovascular disease is the leading cause of morbidity and mortality in patients with diabetes mellitus (DM), and patients with DM frequently develop diabetic cardiomyopathy. Currently, effective treatments for diabetic cardiomyopathy are limited. Vitamin D exerts pleiotropic effects on the cardiovascular system and is associated with DM. The purpose of this review was to evaluate published research on vitamin D in diabetic cardiomyopathy by searching PubMed databases. Herein, we reviewed vitamin D metabolism; evaluated the molecular, cellular, and neuroendocrine effects in native and bioactive vitamin D; and evaluated the role of vitamin D in treating cardiovascular disease and DM. Some evidence suggests that vitamin D may improve cardiovascular outcomes in diabetes through anti-inflammatory, antioxidative, antihypertrophic, antifibrotic, and antiatherosclerotic activities and by regulating advanced glycation end-product signaling, the renin-angiotensin system, and cardiac metabolism. This clinical and laboratory evidence suggests that vitamin D may be a potential agent in treating diabetic cardiomyopathy. However, using vitamin D entails possible adverse risks of hypercalcemia, hyperphosphatemia, and vascular calcifications. Therefore, future studies should be conducted that clarify the potential benefits of vitamin D through large-scale randomized clinical trials in well-defined groups of diabetic patients.

Acute restraint stress induces endothelial dysfunction: role of vasoconstrictor prostanoids and oxidative stress

We hypothesized that acute stress would induce endothelial dysfunction. Male Wistar rats were restrained for 2 h within wire mesh. Functional and biochemical analyses were conducted 24 h after the 2-h period of restraint. Stressed rats showed decreased exploration on the open arms of an elevated-plus maze (EPM) and increased plasma corticosterone concentration. Acute restraint stress did not alter systolic blood pressure, whereas it increased the in vitro contractile response to phenylephrine and serotonin in endothelium-intact rat aortas. NG-nitro-l-arginine methyl ester (l-NAME; nitric oxide synthase, NOS, inhibitor) did not alter the contraction induced by phenylephrine in aortic rings from stressed rats. Tiron, indomethacin and SQ29548 reversed the increase in the contractile response to phenylephrine induced by restraint stress. Increased systemic and vascular oxidative stress was evident in stressed rats. Restraint stress decreased plasma and vascular nitrate/nitrite (NOx) concentration and increased aortic expression of inducible (i) NOS, but not endothelial (e) NOS. Reduced expression of cyclooxygenase (COX)-1, but not COX-2, was observed in aortas from stressed rats. Restraint stress increased thromboxane (TX)B(2) (stable TXA(2) metabolite) concentration but did not affect prostaglandin (PG)F2α concentration in the aorta. Restraint reduced superoxide dismutase (SOD) activity, whereas concentrations of hydrogen peroxide (H(2)O(2)) and reduced glutathione (GSH) were not affected. The major new finding of our study is that restraint stress increases vascular contraction by an endothelium-dependent mechanism that involves increased oxidative stress and the generation of COX-derived vasoconstrictor prostanoids. Such stress-induced endothelial dysfunction could predispose to the development of cardiovascular diseases.

The active form of vitamin D, calcitriol, induces a complex dual upregulation of endothelin and nitric oxide in cultured endothelial cells

Despite the presence of vitamin D receptor (VDR) in endothelial cells, the effect of vitamin D on endothelial function is unknown. An unbalanced production of vasoactive endothelial factors such as nitric oxide (NO) or endothelin-1 (ET-1) results in endothelial dysfunction, which can alter the normal cardiovascular function. Present experiments were devoted to assess the effect of active vitamin D (calcitriol) on the synthesis of endothelial vasoactive factors. The results were that, in cells, calcitriol increased ET-1 and NO productions, which were measured by ELISA and fluorimetric assay, respectively. Calcitriol also increased endothelin-converting enzyme-1 (ECE-1) and endothelial-nitric oxide synthase (eNOS) activities, their mRNA (qPCR), their protein expressions (Western-blot), and their promoter activities (transfection assays). Calcitriol did not change prepro-ET-1 mRNA. The effect was specific to VDR activation because when VDR was silenced by siRNA, the observed effects disappeared. Mechanisms involved in each upregulation differed. ECE-1 upregulation depended on AP-1 activation, whereas eNOS upregulation depended directly on VDR activation. To evaluate the in vivo consequences of acute calcitriol treatment, normal Wistar rats were treated with a single ip injection of 400 ng/kg calcitriol and euthanized 24 h later. Results confirmed those observed in cells, that production and expression of both factors were increased by calcitriol. Besides, calcitriol-treated rats showed a slight rise in mean blood pressure, which decreased when pretreated with FR-901533, an ECE-1 antagonist. We conclude that calcitriol increases the synthesis of both ET-1 and NO in endothelial cells. However, the ET-1 upregulation seems to be biologically more relevant, as animals acutely treated with calcitriol show slight increases in blood pressure.

Vitamin D promotes vascular regeneration

BACKGROUND

Vitamin D deficiency in humans is frequent and has been associated with inflammation. The role of the active hormone 1,25-dihydroxycholecalciferol (1,25-dihydroxy-vitamin D3; 1,25-VitD3) in the cardiovascular system is controversial. High doses induce vascular calcification; vitamin D3 deficiency, however, has been linked to cardiovascular disease because the hormone has anti-inflammatory properties. We therefore hypothesized that 1,25-VitD3 promotes regeneration after vascular injury.

METHODS AND RESULTS

In healthy volunteers, supplementation of vitamin D3 (4000 IU cholecalciferol per day) increased the number of circulating CD45-CD117+Sca1+Flk1+ angiogenic myeloid cells, which are thought to promote vascular regeneration. Similarly, in mice, 1,25-VitD3 (100 ng/kg per day) increased the number of angiogenic myeloid cells and promoted reendothelialization in the carotid artery injury model. In streptozotocin-induced diabetic mice, 1,25-VitD3 also promoted reendothelialization and restored the impaired angiogenesis in the femoral artery ligation model. Angiogenic myeloid cells home through the stromal cell-derived factor 1 (SDF1) receptor CXCR4. Inhibition of CXCR4 blocked 1,25-VitD3-stimulated healing, pointing to a role of SDF1. The combination of injury and 1,25-VitD3 increased SDF1 in vessels. Conditioned medium from injured, 1,25-VitD3-treated arteries elicited a chemotactic effect on angiogenic myeloid cells, which was blocked by SDF1-neutralizing antibodies. Conditional knockout of the vitamin D receptor in myeloid cells but not the endothelium or smooth muscle cells blocked the effects of 1,25-VitD3 on healing and prevented SDF1 formation. Mechanistically, 1,25-VitD3 increased hypoxia-inducible factor 1-α through binding to its promoter. Increased hypoxia-inducible factor signaling subsequently promoted SDF1 expression, as revealed by reporter assays and knockout and inhibitory strategies of hypoxia-inducible factor 1-α.

CONCLUSIONS

By inducing SDF1, vitamin D3 is a novel approach to promote vascular repair.

Vitamin D and inflammatory diseases

Beyond its critical function in calcium homeostasis, vitamin D has recently been found to play an important role in the modulation of the immune/inflammation system via regulating the production of inflammatory cytokines and inhibiting the proliferation of proinflammatory cells, both of which are crucial for the pathogenesis of inflammatory diseases. Several studies have associated lower vitamin D status with increased risk and unfavorable outcome of acute infections. Vitamin D supplementation bolsters clinical responses to acute infection. Moreover, chronic inflammatory diseases, such as atherosclerosis-related cardiovascular disease, asthma, inflammatory bowel disease, chronic kidney disease, nonalcoholic fatty liver disease, and others, tend to have lower vitamin D status, which may play a pleiotropic role in the pathogenesis of the diseases. In this article, we review recent epidemiological and interventional studies of vitamin D in various inflammatory diseases. The potential mechanisms of vitamin D in regulating immune/inflammatory responses in inflammatory diseases are also discussed.

Impact of vitamin D supplementation on arterial vasomotion, stiffness and endothelial biomarkers in chronic kidney disease patients

Background

Cardiovascular events are frequent and vascular endothelial function is abnormal in patients with chronic kidney disease (CKD). We demonstrated endothelial dysfunction with vitamin D deficiency in CKD patients; however the impact of cholecalciferol supplementation on vascular stiffness and vasomotor function, endothelial and bone biomarkers in CKD patients with low 25-hydroxy vitamin D [25(OH)D] is unknown, which this study investigated.

Methods

We assessed non-diabetic patients with CKD stage 3/4, age 17–80 years and serum 25(OH)D <75 nmol/L. Brachial artery Flow Mediated Dilation (FMD), Pulse Wave Velocity (PWV), Augmentation Index (AI) and circulating blood biomarkers were evaluated at baseline and at 16 weeks. Oral 300,000 units cholecalciferol was administered at baseline and 8-weeks.

Results

Clinical characteristics of 26 patients were: age 50±14 (mean±1SD) years, eGFR 41±11 ml/min/1.73 m², males 73%, dyslipidaemia 36%, smokers 23% and hypertensives 87%.

At 16-week serum 25(OH)D and calcium increased (43±16 to 84±29 nmol/L, p<0.001 and 2.37±0.09 to 2.42±0.09 mmol/L; p = 0.004, respectively) and parathyroid hormone decreased (10.8±8.6 to 7.4±4.4; p = 0.001). FMD improved from 3.1±3.3% to 6.1±3.7%, p = 0.001.

Endothelial biomarker concentrations decreased: E-Selectin from 5666±2123 to 5256±2058 pg/mL; p = 0.032, ICAM-1, 3.45±0.01 to 3.10±1.04 ng/mL; p = 0.038 and VCAM-1, 54±33 to 42±33 ng/mL; p = 0.006. eGFR, BP, PWV, AI, hsCRP, von Willebrand factor and Fibroblast Growth Factor-23, remained unchanged.

Conclusion

This study demonstrates for the first time improvement of endothelial vasomotor and secretory functions with vitamin D in CKD patients without significant adverse effects on arterial stiffness, serum calcium or FGF-23.

Trial Registration

ClinicalTrials.gov NCT02005718

Vitamin D receptor activation: cardiovascular and renal implications

The effects of vitamin D receptor activation on cardiovascular diseases, especially hypertension and cardiac dysfunction, are areas of active investigation. This article reviews the current state of knowledge about vitamin D receptor activation with respect to blood pressure, heart, and vascular health, as well as to chronic kidney disease and end-stage renal disease. Potential biological mechanisms, the role of vitamin D-binding protein, and data from observational and randomized controlled trials on this topic are summarized.

Does vitamin D modulate blood pressure?

PURPOSE OF REVIEW

Both vitamin D deficiency and hypertension are highly prevalent. It is unclear whether vitamin D modulates blood pressure and therefore whether vitamin D testing and therapy should become part of routine hypertension prevention and management. This article provides an overview of the data, with special emphasis on the work published in the last 2 years.

RECENT FINDINGS

Several animal studies corroborate the strong effect of vitamin D on the renin-angiotensin-aldosterone axis. Small and large observational studies have found associations between vitamin D, increased blood pressure, and the risk of developing hypertension. In contrast, recent data from randomized trials are mixed. Two randomized trials with approximately 1 year of follow-up detected no association between vitamin D treatment and blood pressure, whereas another study of active vitamin D reported a 9-mmHg decrease in systolic blood pressure. Meta-analyses have linked vitamin D levels with blood pressure, but the effect of vitamin D administration on blood pressure remains controversial.

SUMMARY

Vitamin D deficiency is asociated with high blood pressure in observational studies. This effect is thought to be partly mediated through regulation of the renin-angiotensin-aldosterone axis. However, randomized clinical trials and their meta-analyses have yielded inconclusive results. Large randomized trials focusing on patients with severe vitamin D deficiency and hypertension are needed before vitamin D can be recommended for the prevention or treatment of hypertension.

Suppression of endoplasmic reticulum stress improves endothelium-dependent contractile responses in aorta of the spontaneously hypertensive rat

A contributing factor to increased peripheral resistance seen during hypertension is an increased production of endothelium-derived contractile factors (EDCFs). The main EDCFs are vasoconstrictor prostanoids, metabolites of arachidonic acid (AA) produced by Ca(2+)-dependent cytosolic phospholipase A2 (cPLA2) following phosphorylation (at Ser(505)) mediated by extracellular signal-regulated kinase (ERK1/2) and cyclooxygenase (COX) activations. Although endoplasmic reticulum (ER) stress has been shown to contribute to pathophysiological alterations in cardiovascular diseases, the relationship between ER stress and EDCF-mediated responses remains unclear. We tested the hypothesis that ER stress plays a role in EDCF-mediated responses via activation of the cPLA2/COX pathway in the aorta of the spontaneously hypertensive rat (SHR). Male SHR and Wistar-Kyoto rats (WKY) were treated with ER stress inhibitor, tauroursodeoxycholic acid or 4-phenlybutyric acid (TUDCA or PBA, respectively, 100 mg·kg(-1)·day(-1) ip) or PBS (control, 300 μl/day ip) for 1 wk. There was a decrease in systolic blood pressure in SHR treated with TUDCA or PBA compared with control SHR (176 ± 3 or 181 ± 5, respectively vs. 200 ± 2 mmHg). In the SHR, treatment with TUDCA or PBA normalized aortic (vs. control SHR) 1) contractions to acetylcholine (ACh), AA, and tert-butyl hydroperoxide, 2) ACh-stimulated releases of prostanoids (thromboxane A2, PGF2α, and prostacyclin), 3) expression of COX-1, 4) phosphorylation of cPLA2 and ERK1/2, and 5) production of H2O2. Our findings demonstrate a novel interplay between ER stress and EDCF-mediated responses in the aorta of the SHR. Moreover, ER stress inhibition normalizes such responses by suppressing the cPLA2/COX pathway.

Vitamin D and hypertension: an update and review

PURPOSE OF REVIEW

Vitamin D deficiency and hypertension are highly prevalent. This review will discuss the association between vitamin D deficiency and blood pressure.

RECENT FINDINGS

During the past several years multiple prospective cohorts and randomized studies have been published. Recent studies have focused mostly on 25-hydroxy vitamin D, but a small number of trials used active vitamin D analog compounds.

SUMMARY

Data from cross-sectional studies report that low 25-hydroxy vitamin D is associated with higher systolic blood pressure and higher incidence of hypertension. Large observational studies show a weaker, yet similar association, but they have not largely accounted for the change in vitamin D levels over time. Randomized control trials conflict with observational data probably due to differences in populations studied, doses of vitamin D used, and unmeasured confounders. Further research is needed before clinical practice recommends vitamin D prescription as treatment for hypertension in the general population.

Pharmacological reactivity of resistance vessels in a rat PCOS model - vascular effects of parallel vitamin D₃ treatment

The aim of this study was to clarify the effects of dihydrotestosterone (DHT)-induced polycystic ovary syndrome (PCOS) on pharmacological reactivity of a resistance vessel in a rat model and the possible modulatory role of 1,25-(OH)₂-cholecalciferol (vitamin D₃). The PCOS model was induced in adolescent female Wistar rats by a 10-week DHT treatment. Norepinephrine induced contractility and acetylcholine relaxation were tested in arterioles by pressure arteriography in control as well as DHT- and DHT plus vitamin D₃-treated (DHT+D3) animals. Decreased vasoconstriction and dilatation were detected after DHT treatment. Concomitant vitamin D₃ treatment increased the contractile response and resulted in more relaxed vessels. Endothelial dilation tested with acetylcholine was lower after DHT treatment, this effect was not depend on vitamin D₃ supplementation. In conclusion, hyperandrogenic state resulted in reduced endothelium- and smooth muscle-dependent vasorelaxation and constriction with a complete loss of nitric oxide (NO)-dependent relaxation compared with controls. These alterations caused by chronic DHT treatment were partially reversed by concomitant vitamin D₃ administration.

The effects of vitamin D repletion on endothelial function and inflammation in patients with coronary artery disease

Adequate vitamin D levels may promote cardiovascular health by improving endothelial function and down-regulating inflammation. The objective of this pilot trial was to investigate the effects of vitamin D repletion on endothelial function and inflammation in patients with coronary artery disease (CAD). Using a double-blind placebo wait-list control design, 90 subjects with CAD and vitamin D deficiency (< 20 ng/ml) were randomized 1:1 to 50,000 IU of oral ergocalciferol or placebo weekly for 12 weeks. Endothelial function (reactive hyperemia peripheral arterial tonometry, RH-PAT), circulating adhesion molecules, and pro-inflammatory cytokines were measured at baseline and 12 weeks. The median increase in serum 25-vitamin D from baseline was 26 ± 17 ng/ml in the active group and 4 ± 8 ng/ml in the placebo group (between-group difference = 22 ng/ml, p < 0.001). The median within-subject change in RH-PAT score was 0.13 ± 0.73 with active treatment and −0.04 ± 0.63 with placebo (between-group difference = 0.17, p = 0.44). Within-group and between-group differences in intercellular adhesion molecule levels were greater with placebo (between-group difference = 6 ng/ml, p = 0.048). Vascular cell adhesion molecule levels decreased in both groups by a similar magnitude (median difference between groups = 8.5 ng/ml, p = 0.79). There was no difference between groups in magnitude of reduction in interleukin (IL)-12 (−8.6 ng/ml, p = 0.72) and interferon-gamma (0.52 ng/ml, p = 0.88). No significant differences in blood pressure, e-selectin, high-sensitivity c-reactive protein, IL-6 or the chemokine CXCL-10 were found with treatment. In conclusion, repleting vitamin D levels in subjects with CAD failed to demonstrate any benefits on surrogate markers of cardiovascular health. These results question the role of vitamin D supplementation in modifying cardiovascular disease.

Altered insulin-induced relaxation of aortic rings in a dihydrotestosterone-induced rodent model of polycystic ovary syndrome

OBJECTIVE

To clarify the effects of dihydrotestosterone (DHT)-induced polycystic ovary syndrome (PCOS) on the insulin-dependent vasodilatation of the thoracic aorta and the role of vitamin D in a rat model.

DESIGN

Controlled experimental animal study.

SETTING

Laboratory.

ANIMAL(S)

Thirty adolescent female Wistar rats.

INTERVENTION(S)

The PCOS model was induced by 10 weeks of DHT treatment (83 μg/d). One-half of the DHT-treated animals also received vitamin D (120 ng/kg/wk).

MAIN OUTCOME MEASURE(S)

The aortic rings of the control, DHT, and DHT plus vitamin D-treated animals were isolated. The insulin-dependent vasodilation of the isolated aortic rings was compared in Krebs-Ringer solution and under blockade of nitric oxide (NO) synthase or cyclooxygenase.

RESULT(S)

The insulin-dependent vasorelaxation decreased in both DHT-treated groups independently from the vitamin D treatment; NO-dependent and -independent relaxations were both impaired. In response to prostanoid, vasoconstriction was increased after DHT treatment. The NO-independent relaxation was partially improved by vitamin D treatment, which was neutralized by increased prostanoid-dependent vasoconstriction.

CONCLUSION(S)

Previously, we found that vitamin D treatment prevented systemic insulin resistance; however, in this study, we did not detect any influence on the vascular insulin resistance of the aorta that was induced by DHT treatment. Consequently, controlling insulin resistance with vitamin D alone did not resolve the aortic endothelial dysfunction caused by the hyperandrogenic state.

Effect of vitamin D on aortic remodeling in streptozotocin-induced diabetes

BACKGROUND

Diabetes mellitus is associated with micro- and macrovascular complications and increased cardiovascular risk. Elevated levels of serum asymmetric dimethylarginine (ADMA) may be responsible for endothelial dysfunction associated with diabetes-induced vascular impairment. Vitamin D may have potential protective effects against arterial stiffening. This study aimed to examine both the effects of diabetes on the functional/structural properties of the aorta and the endothelial function and the effects of vitamin D supplementation.

METHODS

Male Wistar rats (n = 30) were randomly assigned to control untreated, diabetic untreated, and diabetic + cholecalciferol groups. Diabetes was induced by intraperitoneal injection of streptozotocin, followed by oral administration of cholecalciferol (500 IU/kg) for 10 weeks in the treatment group. Aortic pulse wave velocity (PWV) was recorded over a mean arterial pressure (MAP) range of 50 to 200 mmHg using a dual pressure sensor catheter. Intravenous infusion of phenylephrine and nitroglycerine was used to increase and decrease MAP, respectively. Serum 25-hydroxyvitamin D [25(OH)D] levels were measured using a radioimmune assay. ADMA levels in serum were measured by enzyme-linked immunoassay. Aortic samples were collected for histomorphometrical analysis.

RESULTS

PWV up to MAP 170 mmHg did not reveal any significant differences between all groups, but in diabetic rats, PWV was significantly elevated across MAP range between 170 and 200 mmHg. Isobaric PWV was similar between the treated and untreated diabetic groups, despite significant differences in the levels of serum 25(OH)D (493 ± 125 nmol/L vs 108 ± 38 nmol/L, respectively). Serum levels of ADMA were similarly increased in the treated and untreated diabetic groups, compared to the control group. The concentration and integrity of the elastic lamellae in the medial layer of the aorta was impaired in untreated diabetic rats and improved by vitamin D supplementation.

CONCLUSION

PWV profile determined under isobaric conditions demonstrated differential effects of uncontrolled diabetes on aortic stiffness. Diabetes was also associated with elevated serum levels of ADMA. Vitamin D supplementation did not improve the functional indices of aortic stiffness or endothelial function, but prevented the fragmentation of elastic fibers in the aortic media.

Endothelium-mediated control of vascular tone: COX-1 and COX-2 products

Endothelium-dependent contractions contribute to endothelial dysfunction in various animal models of aging, diabetes and cardiovascular diseases. In the spontaneously hypertensive rat, the archetypal model for endothelium-dependent contractions, the production of the endothelium-derived contractile factors (EDCF) involves an increase in endothelial intracellular calcium concentration, the production of reactive oxygen species, the predominant activation of cyclooxygenase-1 (COX-1) and to a lesser extent that of COX-2, the diffusion of EDCF towards the smooth muscle cells and the subsequent stimulation of their thromboxane A2-endoperoxide TP receptors. Endothelium-dependent contractions are also observed in various models of hypertension, aging and diabetes. They generally also involve the generation of COX-1- and/or COX-2-derived products and the activation of smooth muscle TP receptors. Depending on the model, thromboxane A(2), PGH(2), PGF(2α), PGE(2) and paradoxically PGI(2) can all act as EDCFs. In human, the production of COX-derived EDCF is a characteristic of the aging and diseased blood vessels, with essential hypertension causing an earlier onset and an acceleration of this endothelial dysfunction. As it has been observed in animal models, COX-1, COX-2 or both isoforms can contribute to these endothelial dysfunctions. Since in most cases, the activation of TP receptors is the common downstream effector, selective antagonists of this receptor should curtail endothelial dysfunction and be of therapeutic interest in the treatment of cardiovascular disorders.

25-Hydroxy vitamin D levels and endothelial vasodilator function in normotensive women

INTRODUCTION

Vitamin D was shown to be related to endothelial function and blood pressure. Reactive hyperaemia index (RHI) measurement by pulse arterial tonometry is a new method to evaluate vasodilator function of endothelium. We aimed to evaluate the relationship between vitamin D levels and RHI in women.

MATERIAL AND METHODS

We enrolled 56 normotensive, nonsmoker, normolipidemic and normoglycemic women, (23 with 25-OH-vitamin D levels>20 µg/l, and 33 with values lower than 20 µg/l). The cardiologist who was blind for vitamin D results executed measurements by pulse arterial tonometry. The measurement was performed on the lying patient with pre- and post-occlusion measurements of RHI by digital sensors placed on each index finger, by 5 min intervals. Pulse amplitudes were recorded, pre-occlusion and post-occlusion ratio was compared by the software of device. Stepwise linear regression and multiple regression analyses were performed to evaluate predictors of endothelial function.

RESULTS

The low vitamin D group had a lower RHI value than the normal vitamin D group (p = 0.042). In regression analysis, positive predictors of RHI were serum 25-OHD (β = 0.401; 95% CI 0.010-0.042, p = 0.002), serum albumin (β = 0.315; 95% CI 0.286-2.350, p = 0.013), and, inversely, serum calcium (β = -0.247; 95% CI (-1.347)-(-0.010), p = 0.047).

CONCLUSIONS

Serum 25-hydroxy vitamin D was significantly related to endothelial functions measured as RHI, even in healthy non-smoker women.

Arteriolar insulin resistance in a rat model of polycystic ovary syndrome

OBJECTIVE

To investigate the vascular dysfunction caused by insulin resistance in polycystic ovary syndrome (PCOS) and the effectiveness of vitamin D in an animal model.

DESIGN

Controlled experimental animal study.

SETTING

Animal laboratory at a university research institute.

ANIMAL(S)

Thirty female Wistar rats.

INTERVENTION(S)

Rats were divided into groups at age 21-28 weeks. Twenty of them were subjected to dihydrotestosterone (DHT) treatment (83 μg/d); ten of them also received parallel vitamin D treatment (120 ng/100 g/wk). Oral glucose tolerance tests with insulin level measurements were performed. Gracilis arterioles were tested for their contractility as well as their nitric oxide (NO)-dependent and insulin-induced dilation using pressure arteriography.

MAIN OUTCOME MEASURE(S)

Several physiologic parameters, glucose metabolism, and pressure arteriography.

RESULT(S)

DHT treatment increased the passive diameter of resistance arterioles, lowered norepinephrine-induced contraction (30.1 ± 4.7% vs. 8.7 ± 3.6%) and reduced acetylcholine-induced (122.0 ± 2.9% vs. 48.0 ± 1.4%) and insulin-induced (at 30 mU/mL: 21.7 ± 5.3 vs. 9.8 ± 5.6%) dilation. Vitamin D treatment restored insulin relaxation and norepinephrine-induced contractility; in contrast, it failed to alter NO-dependent relaxation.

CONCLUSION(S)

In DHT-treated rats, in addition to metabolically proven insulin resistance, decreased insulin-induced vasorelaxation was observed and was improved by vitamin D treatment without affecting NO-dependent relaxation. The reduction in insulin-induced dilation of arterioles is an important as yet undescribed pathway of vascular damage in PCOS and might explain the clinical effectiveness of vitamin D treatment.