Effects of vanadate on myocardial function

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.

Effect of vanadate on reproductive efficiency in normal and streptozocin-treated diabetic rats

The effects of oral vanadate treatment on the reproductive efficiency of normal and diabetic female rats were studied. Vanadate treatment in a dose-dependent manner reduced both the conception rate and the ability to carry pregnancy to term compared with a control group. These effects were more severe in diabetic groups as compared with nondiabetic groups. At the 0.25 mg/mL vanadate dose, the conception rate was reduced by 13% and 33% for the nondiabetic group and the diabetic group, respectively. At the 0.50 mg/mL dose, this rate decreased by 20% and 47% for the nondiabetic and diabetic groups, respectively. With an identical oral vanadate regimen of 0.25 mg/mL, the ability to sustain pregnancy to term was reduced by 30% and 90% for the nondiabetic and diabetic groups, respectively, and by 84% and 100% for these groups at a dose of 0.50 mg/mL. Although the blood vanadate concentrations were an order of magnitude higher in diabetic animals treated with vanadate than in nondiabetic animals under an identical vanadate treatment, oral vanadate treatments had no measurable effects in ameliorating hyperglycemia in these diabetic pregnant animals. In conclusion, vanadate is ineffective in normalizing blood glucose in pregnant diabetic rats, and it impairs reproductive capacity and the ability to sustain pregnancy to term in both nondiabetic and diabetic animals.

Effects of maternal vanadate treatment of fetal development

Oral vanadate treatment is effective in normalizing blood glucose in both Type I and Type II diabetics. Using Sprague Dawley rats we examined the effectiveness of such treatment in amelioration of hyperglycemia in diabetic pregnancy and its effect on fetal growth in both normal and diabetic pregnant dams. Initiation of vanadate treatment to diabetic and normal pregnant dams increased blood vanadium levels in both groups, but this concentration in the diabetic pregnant group reached approximately twice the value present in the normal group. Despite this high blood vanadium level in the diabetic pregnant dams, oral vanadate treatment was not effective in normalizing blood sugar in this group. Additionally, vanadate treatment was found to be toxic during diabetic pregnancy, causing death to 45% of the test animals. Maternal blood vanadium had a negative effect on fetal development, markedly reducing the number of live fetuses per pregnancy. In summary, oral vanadate treatment is toxic and ineffective during diabetic pregnancies and interferes with fetal growth and development in both normal and diabetic pregnancy.

Stimulation of mutases and isomerases by vanadium

The effects of vanadate and vanadate complexes on the rates of exchange of phosphoryl groups in the reactions catalyzed by the enzymes phosphoglucomutase and the coupled system formed by phosphoglycerate mutase and enolase, and the effects of vanadyl complexes on the interconversion of aldehyde and keto groups catalyzed by the enzymes phosphomannose isomerase, phosphoribose isomerase, and phosphoglucose isomerase, were measured using one-dimensional 31P nuclear magnetic resonance spectroscopy. Chemical exchange was investigated by observing the transfer of magnetization achieved by selective irradiation of resonances using the DANTE pulse sequence. The presence of vanadium stimulated the catalytic activity of the enzymes in vitro, with the exception of enolase whose activity was not affected. Addition of vanadate also increased the rate constants of the interconversion of glucose 6-phosphate and fructose 6-phosphate in hemolysates. 51V nuclear magnetic resonance spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the interactions between ammonium vanadate and sugar phosphates and the formation of vanadium--sugar phosphate complexes that may be involved in the stimulation of the catalytic activity of the isomerases.

Diabetes-induced abnormalities in the myocardium

One of the leading causes of mortality in diabetics is myocardial disease. In the past few years this subject has generated a significant amount of interest with the result that myocardial problems associated with diabetes are far better understood. Though originally thought to occur as a result of atherosclerosis, various studies have shown that heart disease can occur in the absence of atherosclerosis, suggesting a diabetic cardiomyopathy. Using diabetic animals, it has been possible to characterize diabetes-induced myocardial abnormalities. Diabetic rat hearts do not respond to conditions of high stress as well as controls. The functional depression is accompanied by altered cardiac enzyme systems. A decrease in myosin ATPase activity which appears to be a result of diabetes-induced hypothyroidism is seen. Also, a depression of sarcoplasmic reticular calcium ATPase, along with a depression of calcium uptake by the SR, is seen in diabetic rat hearts. Na+, K+ ATPase activity has also been shown to be depressed and the depression appears to correlate with depressed atrial contractility. High levels of circulating fats in diabetics may alter the integrity of membranes leading to altered enzyme activities. Insulin treatment has been relatively successful at reversing or preventing myocardial changes in the diabetic rat. Other treatments that have been studied include thyroid hormone treatment, since the depression of myosin ATPase can be corrected by such treatment; and carnitine treatment, as the elevation of long chain acyl carnitines (LCAC) and the resulting depression of calcium uptake in the SR can be so normalized. These treatments have not been successful at normalizing cardiac function. A combination of the two treatments normalized function only partially, suggesting that factors besides myosin ATPase and SR calcium uptake are involved. Other treatments that have been tried include vanadate, methyl palmoxirate, and choline and methionine. Vanadate treatment has proved to be encouraging in that it normalizes both function and hyperglycemia. Methyl palmoxirate, a fatty acid analog, normalized only the elevation of LCAC but did not affect function. Methionine and choline were only partially successful in preventing the functional alterations of diabetic rat hearts. The purpose of the present article is to review our understanding of diabetes-induced myocardial problems and their possible causes. Findings from our laboratory and others are described in which attempts have been made to normalize cardiac function.

Hemodynamic effects of vanadate administration in rats with different levels of sodium intake

The acute hemodynamic effect of an intravenous (IV) bolus of vanadate (10 mumol/kg bwt) followed by an IV infusion at 0.5 mumol/kg min was studied in Wistar rats at three different levels of Na intake: low Na+ (0.5 mEq/24 h), normal Na+ (1.5 mEq/24 h), and high Na+ (15 mEq/24 h). Hemodynamic changes were measured using the radioactive microsphere method. Vanadate decreased cardiac output by 52.0 +/- 6.4% in low Na+ rats, by 41.2 +/- 3.3% in normal Na+, and by 29.2 +/- 3.1% in high Na+ group. Total peripheral resistances increased by 47.1 +/- 26% in high Na+ rats, by 80.1 +/- 6.6% in normal Na+, and by 96.3 +/- 4.5% in low Na+ group. Renal blood flow decreased by 70 +/- 4% in low Na+, 58 +/- 3% in normal Na+, and 39 +/- 3% in high Na+. Cerebral, testicular, and splanchnic blood flow showed smaller changes. These results demonstrate that intravenous vanadate induces marked hemodynamic changes that depend on Na+ intake being more striking when the intake of sodium is reduced.

Inhibition of rat cardiac and renal Na+,K+-ATPase by high sodium concentrations and vanadate

In the present study, rat renal Na+,K+-ATPase was found to be more sensitive to inhibition by high Na+ concentrations (100-400 mM) than was rat cardiac Na+,K+-ATPase. K+ was more effective in reversing the inhibition by Na+, of cardiac relative to renal Na+,K+-ATPase. Rat renal Na+,K+-ATPase was also more sensitive than cardiac Na+,K+-ATPase to inhibition by vanadate over this range of Na+ concentrations. These results support the hypothesis that vanadate may selectively regulate Na+,K+-ATPase in the kidney, and they may also help explain the natriuretic and diuretic effects of vanadate in rats. Inhibition of renal Na+,K+ATPase by Na+, may also help explain, in part, the natriuretic and diuretic effects of acute saline loading.

Effect of vanadate on elevated blood glucose and depressed cardiac performance of diabetic rats

The trace element vanadium has an unclear biological function. Vanadate, an oxidized form of vanadium, appears to have an insulin-like action. The effect of vanadate on blood glucose and cardiac performance was assessed in female Wistar rats 6 weeks after they were made diabetic with streptozotocin. When vanadate was administered for a 4-week period to the diabetic rats, their blood glucose was not significantly different from that of nondiabetic controls despite a low serum insulin. In contrast, blood glucose was increased about threefold in the diabetic rats that were not treated with vanadate; these rats also had low insulin levels. Cardiac performance was depressed in the untreated diabetic animals, but the cardiac performance of the vanadate-treated diabetic animals was not significantly different from that of nondiabetic controls. Thus vanadate controlled the high blood glucose and prevented the decline in cardiac performance due to diabetes.

Greater sensitivity to vanadate of rat renal relative to cardiac (Na+ + K+)-ATPase

Vanadate (VO4(-3] produces a positive inotropic effect in rats and also promotes diuresis as well as natriuresis. Although the mechanism(s) of these effects is uncertain, in the kidney, VO4(-3) may act through inhibition of (Na+ + K+)-ATPase activity, whereas in the heart, other or additional mechanisms are likely. Under the assay conditions used in the present study, microsomal (Na+ + K+)-ATPase activities from rat kidney cortex and medulla were inhibited to a greater extent than was left ventricular (Na+ + K+)-ATPase activity over a range of VO4(-3) concentrations. The apparent dissociation constant for left ventricular (Na+ + K+)-ATPase (10.95 +/- 1.26 X 10(-7)M VO4(-3] was significantly greater than that of (Na+ + K+)-ATPase from the cortex (3.46 +/- 0.96 X 10(-7)M VO4(-3] or the medulla (3.32 +/- 0.7 X 10(-7)M VO4(-3), N = 6, P less than .05) whereas there were no significant differences between the effects of VO4(-3) on (Na+ + K+)-ATPase from the cortex and medulla. The greater inhibition by VO4, of (Na+ + K+)-ATPase from the cortex relative to that of the left ventricle, occurred over a range of Na+ and K+ concentrations, and K+ enhanced the inhibition by VO4(-3) to a greater extent for (Na+ + K+)-ATPase from the cortex than the left ventricle. These results suggest that renal (Na+ + K+)-ATPase is more sensitive than left ventricular (Na+ + K+)-ATPase to inhibition by VO4(-3) and would, therefore, be more likely to be modulated in vivo.

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.

Stimulatory (insulin-mimetic) and inhibitory (ouabain-like) action of vanadate on potassium uptake and cellular sodium and potassium in heart cells in culture

(1) The influence of vanadate (Na3VO4) on sodium and potassium uptake as well as on cellular ion contents of sodium and potassium has been studied in heart muscle and non-muscle cells obtained from various species. An ouabain-like inhibition of potassium uptake (up to 50%), combined with a decrease of cellular potassium (up to 20%) has been observed by vanadate (10(-4)-10(-3) M) in heart non-muscle cells obtained from neonatal guinea pigs and chick embryos. In heart muscle and non-muscle cells prepared from neonatal rats, as well as in Girardi human heart cells, a vanadate-induced stimulation of potassium uptake (up to 100%), combined with a rise in cellular potassium (up to 20%) and without significant alteration of cellular sodium, has been found. A slight increase of 22Na+ influx can be measured in rat heart muscle cells and in Girardi human heart cells in the presence of vanadate (10(-4)--10(-3) M). (2) In beating rat heart muscle cells in culture, detrimental effects of serum deprivation--concerning beating properties, potassium uptake and cellular potassium--can at least in part be overcome by addition of vanadate. Furthermore, this compound prevents ouabain-induced signs of toxicity (contractures) in these cells. (3) The stimulatory effects of vanadate on potassium can be mimicked by insulin (1-10 mU/ml). Furthermore, vanadate produces an insulin-like stimulation of 2-deoxy-D-glucose uptake in rat heart muscle and non-muscle cells as well as in Girardi human heart cells. (4) The experimental data demonstrate an ouabain-like inhibition as well as an insulin-mimetic stimulation of potassium-uptake in various heart cells. The reason for this antagonistic mode of action may be due to the different capabilities of the heart cell types to reduce vanadium in the V-valence state of vanadium in the IV-valence state, thereby favouring either ouabain-like inhibition (vanadium V) or insulin-mimetic stimulation (vanadium IV) of potassium transport.

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

Vanadate, a potent naturally occurring Na+,K+-ATPase inhibitor thought to have a role in regulating Na+-K+ pump activity, was fed to uninephrectomized rats drinking tap water or a 1% solution of sodium chloride for as long as 56 weeks. Feeding was achieved by adding sodium orthovanadate to normal rat chow equivalent to 100 or 200 ppm vanadium by weight. In the rats drinking tap water, systolic pressure gradually increased over a period of several weeks and then was sustained in a dose-related manner for the duration of the treatment. The increased pressure was not associated with changes in water intake, urine output, or urinary sodium excretion but correlated positively with plasma vanadium levels ranging from 0.04 to 0.27 microgram/ml. Increased pressure was associated with increased heart-to-body-weight ratio but did not appear to occur in a small group of animals drinking the 1% solution of sodium chloride. These findings, considered in the light of others, indicate that vanadate deserves continued study in relation to hypertension.