Effect of prolonged dietary administration of vanadate on blood pressure in the rat

Concentrations of vanadium in urine with hypertension prevalence and blood pressure levels

The associations of vanadium exposure with hypertension risk in animal studies are inconsistent. Furthermore, epidemiologic studies on this topic are scarce. We aimed to assess the associations of vanadium exposure with hypertension prevalence and blood pressure levels in a general Chinese population. We measured urinary vanadium concentrations in 1867 participants to evaluate their internal exposure levels. The associations of urinary vanadium concentrations, categorized into quartiles or treated as continuous variables by logarithm transformation (log2), with hypertension prevalence and blood pressure levels were assessed by the multivariable logistic and linear regression models, respectively. We used the restricted cubic spline model to evaluate the dose-response relationship. Compared with the bottom quartile of vanadium, participants in the third and fourth quartile had an adjusted odds ratio of 2.04 (95% CI:1.40, 2.96) and 2.08 (95% CI:1.42, 3.06) for hypertension, with a linear dose-response relationship. The corresponding number for a doubling of vanadium concentrations was 1.25 (95% CI:1.12, 1.39). Besides, a doubling of vanadium concentrations was associated with a 0.66 (95% CI: 0.01, 1.31) and 0.90 (95% CI: 0.50, 1.31) mm Hg increased systolic and diastolic blood pressure level, respectively. Vanadium exposure was associated with increased hypertension prevalence and blood pressure levels. Prospective studies are needed to confirm our findings in other populations.

Differential effects of sodium tungstate and vanadyl sulfate on vascular responsiveness to vasoactive agents and insulin sensitivity in fructose-fed rats

High fructose feeding induces insulin resistance, impaired glucose tolerance, and hypertension in rats and mimics most of the features of the metabolic syndrome X. The effects of a 6-week treatment with the transition metals administered in drinking water, vanadium (VOSO4·5H2O, 0.75 mg/mL) or tungsten (Na2O4W, 2 g/mL), were investigated on the reactivity to norepinephrine (NEPI) or acetylcholine (ACh) of thoracic aorta rings isolated from fructose (60%) or standard chow fed rats. Maximal effect (Emax) and pD2(–log EC50) values were determined in each case in the presence or absence of endothelium, while the degree of insulin resistance was determined using the euglycemic hyper insulinemic glucose clamp technique. Aortic segments isolated from 6-week fructose-fed animals were characterized by NEPI hyperresponsiveness (increase in Emax) and endothelium-dependent NEPI supersensitivity (increase in pD2) without any change in the reactivity to ACh. Vanadium or tungsten administered in fructose-fed animals prevented both hypertension and NEPI hyperresponsiveness, while vanadium, but not tungsten, reduced NEPI supersensitivity. Vanadium, but not tungsten, increased the relaxing activity of ACh, both in control and fructose-fed animals. Insulin resistance associated with high fructose feeding was reversed by vanadium but not by tungsten treatment. The differential effects of the two transition metals on vascular responsiveness to NEPI or ACh may be explained by their differential effects on insulin sensitivity.Key words: vanadium, tungsten, aorta, hypertension, fructose, glucose clamp.

Vanadium and the cardiovascular functions

Inorganic and organic compounds of vanadium have been shown to exhibit a large range of insulinomimetic effects in the cardiovascular system, including stimulation of glucose transporter 4 (GLUT-4) translocation and glucose transport in adult cardiomyocytes. Furthermore, administration of vanadium compounds improves cardiac performance and smooth muscle contractility, and modulates blood pressure in various models of hypertension and insulin resistance. Vanadium compounds are potent inhibitors of protein tyrosine phosphatases. As a result, they promote an increase in protein tyrosine phosphorylation of several key components of the insulin signaling pathway, leading to the upregulation of phosphatidylinositol 3-kinase and protein kinase B, two enzymes involved in mediating GLUT-4 trans location and glucose transport. In addition, vanadium has also been shown to activate p38 mitogen-activated protein kinase and increase Ca2+levels in several cell types. The ability of vanadium compounds to activate these signaling events may be responsible for their ability to modulate cardiovascular functions.Key words: vanadium compounds, glucose transport, smooth muscle contractility, insulin signaling pathway.

Effect of sodium orthovanadate treatment on cardiovascular function in the hyperinsulinemic, insulin-resistant obese Zucker rat

We recently demonstrated that oral vanadate treatment ameliorates exaggerated vasoconstriction in aortic tissue from the hyperinsulinemic/insulin resistant obese Zucker rat. It has been suggested that changes in large artery contractility might contribute to the development of hypertension in this strain. Thus we examined the effect of vanadate treatment (0.5 mg/ml, p.o.) on conductance and resistance vessel function as well as blood pressure (BP) in Zucker rats. Vasoconstrictor responses to endothelin-1 (ET-1) and methoxamine and vasodilator responses to acetylcholine in the aorta and perfused mesenteric vascular bed served as indices of conductance and resistance function, respectively. Separate groups were treated with insulin (12 mU/kg/min, s.c.) to determine its role in the actions of vanadate. Vanadate treatment reduced (2.5-fold; p < 0.05) elevated plasma insulin levels and abolished exaggerated aortic vasoconstriction in obese rats. Vasoconstrictor responses in the mesenteric bed, however, were similar between obese and lean rats, and were unaffected by vanadate. Vanadate did not affect elevated BP in obese rats and actually increased BP in the lean group. Insulin treatment per se failed to affect vasomotor function or BP in either strain, and acetylcholine-evoked relaxation was similar in all groups. We conclude that whereas vanadate overcomes exaggerated central artery contractility in obese Zucker rats, it fails to affect resistance vessel function or BP in this strain, and might conversely elevate BP in normotensive lean control rats. The vascular actions of vanadate in obese rats appear to occur independent of changes in plasma insulin or endothelial function.

Vanadate as factor of cardiovascular regulation by interactions with the catecholamine and nitric oxide systems

The effects of 1 microgram/mL of vanadium, given for 12 mo as sodium metavanadate in drinking water, on cardiovascular and biochemical indices of male rabbits were investigated. At the end of the exposure period, vanadium was more accumulated in bones and kidneys than in spleen and liver; the cardiac ventricles and the aorta contained similar amounts of this element. Blood pressure and heart rate were unchanged in the vanadate-exposed animals since the observed decrease of both cardiac inotropism and stroke volume was counteracted by an increase of peripheral vascular resistance, with reduction of arterial blood flow. The arterial levels of sodium, potassium and aldosterone were unmodified by vanadate which, however, strongly raised those of noradrenaline, adrenaline, L-DOPA, and dopamine. Vanadate caused a marked increase of the activity of monoamine oxidase in renal tubules and liver (probably in relation to the increased plasma catecholamine levels) and a reduction of that of glucose-6-phosphate dehydrogenase in the kidney. There was also evidence that vanadium reduces synthesis and/or release of nitric oxide, the endothelium-derived vasodilating factor, likely through a reduced formation from bradykinin. It was concluded that vanadium may represent an environmental factor of altered cardiovascular homeostasis.

The influence of the blood levels of lead, aluminum and vanadium upon the arterial hypertension

The present study describes the relationship between the whole blood Pb, plasma Al and plasma V levels and the arterial hypertension, for four groups of individuals: 20 normotensive azotemic patients in periodic hemodialysis (CRF), 20 hypertensive azotemic patients in periodic hemodialysis (CRF-AHT), 20 individuals with severe essential hypertension and normal renal function (AHT) and 20 individuals with normal renal function and normal blood pressure (controls) evaluated during a period of 1 year. The renal population's blood Pb was comparable with that found in the non-renal groups. Blood Pb in the essential AHT was higher than in controls (P < 0.05). CRF and CRF-AHT showed higher Al levels than those individuals with normal renal function (P < 0.01). In CRF, plasma Al did not correlate with the arterial hypertension. Plasma Al was increased in the AHT individuals (P < 0.05) with respect to the control group, suggesting the possible influence of this metal in the appearance of the arterial hypertension. In this study, the CRF-AHT patients had plasma V statistically higher (P < 0.005) than controls. However, no differences were found between plasma V of CRF and CRF-AHT groups or between AHT and controls. These results suggest that V in AHT is of doubtful significance, except maybe when the renal failure and the arterial hypertension appear together. In summary, high levels of blood Pb and plasma Al are associated with arterial hypertension in individuals without renal disease. Higher plasma V levels were not found in hypertensives with normal renal function with respect to controls.

Vanadate increases cytosolic free calcium in rat aortic smooth muscle cells

Although several studies have shown that vanadate evokes vasoconstriction whether it elevates cytosolic free calcium, [Ca2+]i, in vascular smooth muscle (VSM) cells has not been investigated. The present study shows that acute additions of low concentrations of vanadate (10-200 microM) to cultured aortic smooth muscle cells (ASMC) produced a rapid and a concentration-dependent increase in [Ca2+]i with an EC50 (mean +/- SEM) value of 42 +/- 11 microM. Inclusion of vanadate (200 microM) led to a significant increase (p < 0.05) in the peak [Ca2+]i level to 190 +/- 23 nM from a basal level of 102 +/- 2 nM. At concentrations > 200 microM, vanadate caused quenching of fura-2 fluorescence. For example, addition of 1 mM vanadate led to an apparent decrease in fluorescence by about 50% (due to a quenching effect), followed by a transient rise. H2O2, which is used in the preparation of peroxide forms of vanadate, pervanadate (PV), also produced a rise in [Ca2+]i. These data suggest that vanadate promotes vascular tone by elevating [Ca2+]i in ASMC. However, [Ca2+]i measurements made with higher concentrations of vanadate and PV, using the fura-2 method, must be interpreted with caution.

Effect of vanadium on regional brain glucose utilization in rats

Recent study has indicated that administration of vanadate, an insulomimetic agent, stimulates glucose uptake in the brain, concurrently with a suppression of food intake. The present work was carried out to characterize which specific brain areas are implicated in this increased glucose utilization. After 3 days of vanadate or vanadyl treatment, anaesthetized fasted rats were injected with tritiated 2-deoxyglucose and different brain areas were punched. Vanadate had no effect on glucose utilization but vanadyl significantly increased glucose uptake in the olfactory bulbs, the hypothalamus, and the hindbrain compared to the pair fed controls.

Vanadate stimulates in vivo glucose uptake in brain and arrests food intake and body weight gain in rats

Vanadate, administered via drinking fluid (0.2-0.8 mg/ml in 80 mM NaCl), attenuated food intake and strongly suppressed body weight gain in normally-fed or 20-hour food-deprived rats. At 0.8 mg/ml for 4 days, oral vanadate significantly stimulated the rate of hexose uptake by brain tissue. When microinjected into the lateral cerebral ventricle at a dose of 82 nmol, vanadate strongly and specifically suppressed food intake and body weight gain in 20-hour food deprived rats previously maintained on tap water. This inhibitory effect was reversed by coadministration of 3-O-methyl glucose. Collectively, the results suggest that vanadate is capable of blocking food intake by a specific effect in the central nervous system that involves stimulation of local glucose uptake.

Some selected peripheral blood and haemopoietic system indices in Wistar rats with chronic vanadium intoxication

1. Wistar rats of both sexes received vanadium in drinking water in the amount of 23-29 mg/kg body weight in the form of ammonium metavanadate (AMV) for a period of 2, 4 and 8 weeks. 2. Animals treated in this way ate less food and drank less AMV solution as compared with the amount of water consumed by the controls; they suffered from diarrhoea, and owing to this the increment in body weight was reduced. 3. Vanadium decreased erythropoiesis and maturation of red blood cells, which was expressed by a reduced erythrocyte count and haemoglobin level and increased reticulocyte and polychromatophilic erythrocyte count in the peripheral blood. 4. The composition percentage of the bone marrow cells and the peripheral blood leukocyte count did not undergo noticeable changes under the influence of vanadium.

Minireview: physiological and pharmacological properties of vanadium

Vanadium is distributed extensively in nature. It is a trace element and is present in almost all living organisms including man. Even though vanadium was originally recognized for its ability to inhibit membrane Na+-K+-ATPase, various laboratory studies now document that this element has the capacity to affect the activity of various intracellular enzyme systems and may modify their physiological functions. Vanadium may be an essential element for normal development and may play an important role in various homeostatic mechanisms, and thus vanadium deficiency may prove to be an important concern. Abnormalities in biological disposition of vanadium may be involved in the pathogenesis of certain neurological disorders or cardiovascular diseases. While the essentiality of this element for living organisms is yet to be established with certainty, vanadium has become an increasingly important element and is used extensively in various heavy industries such as steel, oil, etc.; thus, the incidence of exposure to toxic levels of vanadium to industrial workers has been an increasing concern for toxicologists. To date, little information is available on the physiological or pharmacological actions of vanadium; hence, it is difficult to reach any definitive conclusion concerning its biological significance, essentiality and its role in pathological states. An attempt has been made in this review to broadly document what is known of various biological actions of vanadium.

Vanadate effect on the Na,K-ATPase and the Na-K pump in in vitro-grown rat vascular smooth muscle cells

The impact of vanadate on the Na,K-ATPase system in the vascular smooth muscle cell is poorly understood. The present study describes the kinetics of the effect of vanadate on Na,K-ATPase and the Na-K pump in in vitro grown rat VSMC's. Vanadate interaction with the Na,K-ATPase system in vascular smooth muscle cells was examined by observing its influence on ouabain-sensitive adenosine triphosphate hydrolysis in disrupted cells rendered permeable by osmotic shock, and the uptake of rubidium by intact cells. The I50 for vanadate inhibition of ouabain-sensitive hydrolysis of adenosine triphosphate occurred at vanadate concentrations of 10(-6) to 10(-7) M. This inhibition was potassium dependent. The maximal inhibitory effect of vanadate occurred at potassium concentrations of 10-20 mEq/liter. Sodium exerted a moderate antagonistic influence on vanadate inhibition of ouabain-sensitive adenosine triphosphate hydrolysis. Rubidium uptake by vascular smooth muscle cells was not altered within 120 minutes when 10(-5) M vanadate was added to the medium containing intact vascular smooth muscle cells. Yet, vanadium concentrations in the vascular smooth muscle cells within this incubation period reached levels 1.48-fold higher than the extracellular vanadate concentrations of 10(-5) M. These observations indicate that vanadate is a potent inhibitor of the VSMC Na,K-ATPase in disrupted vascular smooth muscle cells. However, in intact vascular smooth muscle cells vanadium gaining access into the vascular smooth muscle cell's interior does not inhibit the Na-K pump, probably because of its binding to intracellular proteins and/or conversion from the vanadate to the vanadyl ion.

Humoral factors and the sodium-potassium pump in low renin hypertension

Recent studies suggest that sodium dependent low renin hypertension results in part from the release of a ouabain-like factor, perhaps natriuretic hormone, from the brain. This humoral factor inhibits Na+, K+-ATPase and hence the active pumping of sodium and potassium in the muscle cells of blood vessels and heart. The pump suppression causes increased contractile activity and hence increased arterial blood pressure. In the muscle cells of the blood vessels, the increased contractile activity appears to be related to membrane depolarization.