The change of beta-adrenergic system in lead-induced hypertension

Lead acetate versus cadmium sulfate in the modulation of main physiological pathways controlling detrusor muscle contractility in rat

Heavy metals have a deleterious effect on lower urinary tract functions. Scant data has been reported about metals’ effect on altering detrusor muscle contractility. Rats were given lead acetate (3, 30 mg/kg), cadmium sulfate (0.1, 1 mg/kg) or ferrous sulfate-iron overload-(3, 30 mg/kg), in a subacute toxicity study (21 days, ip). In-vitro tension experiments were conducted using isolated rat detrusor muscle. Measurement of heavy metal concentrations in blood and tissue homogenates was performed, as well as histopathological examinations. Subacute toxicity induced by treatment with lead and cadmium was manifested as a decrease in EFS, ACh, and ATP-mediated contraction of isolated detrusor muscle. Iron overload only decreased E_MAX of EFS and ACh-mediated contraction. Lead (30 mg/kg) caused an upward shift in the dose response curve of isoprenaline-induced relaxation, with a significant decrease in E_MAX. Lead (30 mg/kg) or cadmium (1 mg/kg) inhibited adenosine (10⁻⁵ M)-induced relaxation. Comparisons to control tissues showed a selective accumulation of metals in the detrusor muscle. Histopathological examinations revealed edema and inflammation in the urinary bladder. Directly added lead (10 mM) inhibited detrusor muscle contraction in-vitro, and its effect was decreased in presence of atropine, and potentiated in presence of TEA, L-NAME, or MB. Cadmium's (0.1 mM) inhibitory effect was reduced in presence of nifedipine or trifluoperazine. In conclusion, lead, cadmium, or iron induce detrusor hypoactivity: The inhibitory effect of lead may be mediated by modulating muscarinic receptors but not the K⁺/NO/cGMP pathway, whereas cadmium inhibitory effect may be mediated by inhibiting the Ca²⁺/calmodulin pathway.

Lead (Pb) exposure and heart failure risk

Lead (Pb) is a heavy metal with widespread industrial use, but it is also a widespread environmental contaminant with serious toxicological consequences to many species. Pb exposure adversely impacts the cardiovascular system in humans, leading to cardiac dysfunction, but its effects on heart failure risk remain poorly elucidated. To better understand the pathophysiological effects of Pb, we review potential mechanisms by which Pb exposure leads to cardiac dysfunction. Adverse effects of Pb exposure on cardiac function include heart failure risk, pressure overload, arrhythmia, myocardial ischemia, and cardiotoxicity. The data reviewed clearly establish that Pb exposure can play an important role in the occurrence and development of heart failure. Future epidemiological and mechanistic studies should be developed to better understand the involvement of Pb exposure in heart failure.

Histopathological changes associated with exposure to metal welding fumes in some organs of Rattus norvegicus in Kano, Nigeria

Welding fumes has been known to cause release of reactive oxygen species which stands to be cytotoxic. The study aims to assess the histopathological changes of some organs associated with exposure to welding fumes in experimental animals. The metal fumes were obtained from sites of welding. A total of 130 male albino rats were engaged and divided into a 13 groups. Out of which 12 were given respective doses calculated to be equivalent to worker's real life exposure times and 1 as control. The doses were intratracheally administered weekly following anesthetization for a period of 12 weeks. The laboratory rats were then sacrificed and target organs were examined. Histopathological examination reveals normal feature for brain tissues in all treated animals. However, there was lymphocyte hyperplasia and necrosis in heart, kidney, liver and lungs tissues which at lower doses were slight and became moderate at higher doses. In addition, there were'nt pathological changes in tissues of the control animals. Thus, exposure to metal welding fumes has caused damages that have translated into lesions and several pathologies in kidney, lungs, liver and heart tissues of the test animals. Regulation and control should be imposed on exposure to welding fumes by metal workers.

Blood Pressure and Lipid Profile in Automechanics in Relation to Lead Exposure

Context

Elevated blood pressure and alterations in lipid and lipoproteins play a major role in the development and progression of cardiovascular diseases.

Aim

This study is aimed at determining the blood pressure and lipid profile in automechanics.

Settings and Design

A total of 120 male subjects between 18 and 55 years of age comprised 60 automechanics and 60 age-matched occupationally unexposed control subjects in Emene, Enugu State, Nigeria.

Subjects and Methods

Four milliliters of fasting blood samples was collected from all subjects, 2 mL of blood was dispensed into K₂-EDTA vacutainer tube for blood lead analysis, while the other 2 mL was dispensed into plain vacutainer tube, allowed to retract, centrifuged, and the serum used for serum lipid profile analysis. Blood pressure was measured using aneroid sphygmomanometer.

Statistical Analysis

Statistical Package for Social Sciences (SPSS) version 21.0 was used for data analysis.

Results

Automechanics had significantly higher values of systolic and diastolic blood pressures compared with the controls. Serum levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), very low-density lipoprotein cholesterol (VLDL-C), and triglyceride (TG) were also significantly higher in the automechanics compared with the controls (P < 0.05); serum high-density lipoprotein cholesterol (HDL-C) level, however, did not differ significantly between the two groups (P > 0.05). Blood lead level showed a significant positive correlation (P < 0.05) with systolic and diastolic blood pressures, serum TC, LDL-C, VLDL-C, and TG, with no significant correlation with serum HDL-C (P > 0.05) in the automechanics and no correlation in the controls.

Conclusion

The result of this study indicates that blood pressure is elevated and lipid profile altered in automechanics which suggests that these groups of workers are prone to increased risk of developing hypertension and cardiovascular disorders due to occupational exposure to lead.

Relation Between Lead Exposure and Trends in Blood Pressure in Children

Obesity raises blood pressure (BP) in children and adults. Nevertheless, as obesity increased around the globe, population systolic and diastolic blood pressures were flat or fell. Examining children is insightful because pediatric trends are largely unconfounded by antihypertensive therapy. Decomposing BP into arterial types, large artery measures (pulse pressure) increased in concert with obesity while small artery measures (mean arterial pressure, [MAP]) decreased, suggesting small arteries are the locus of the countervailing temporal trends. Pediatric lead exposure decreased as pediatric obesity rose. Over the period of rising obesity, we examined the association between lead exposure and temporal trends in BP. We analyzed anthropometric, BP, and laboratory data on 8-17 year old children from the serial cross-sectional National Health and Nutrition Examination Surveys 1976 through 2008. Multivariable adjusted survey regression was used to examine temporal trends in blood pressure in relation to blood lead concentrations (N = 13,501). As obesity prevalence rose from 5.3% to 24.5%, age-sex adjusted systolic BP was flat (-0.01 [95% confidence interval (CI) -0.06, 0.04] mm Hg/yr, p = 0.8), diastolic BP and MAP decreased (respectively -0.28 [-0.32, -0.24] and -0.19 [CI -0.23, -0.15], both p<0.0001) while pulse pressure increased (0.28 [0.23, 0.32], p<0.001). Accounting for blood lead concentration attenuated the decreasing MAP trend by 67%. In conclusion, the contrary trends in pediatric BP during the rise of pediatric obesity may be substantially attributable to decreasing lead exposure acting on small resistance arteries. These results have implications for globally observed BP trends in youth and adults. Environmental policy altering lead levels may have long-lasting cardiovascular benefits.

Chronic lead exposure enhances the sympathoexcitatory response associated with P2X4 receptor in rat stellate ganglia

Chronic lead exposure causes peripheral sympathetic nerve stimulation, including increased blood pressure and heart rate. Purinergic receptors are involved in the sympathoexcitatory response induced by myocardial ischemia injury. However, whether P2X4 receptor participates in sympathoexcitatory response induced by chronic lead exposure and the possible mechanisms are still unknown. The aim of this study was to explore the change of the sympathoexcitatory response induced by chronic lead exposure via the P2X4 receptor in the stellate ganglion (SG). Rats were given lead acetate through drinking water freely at doses of 0 g/L (control group), 0.5 g/L (low lead group), and 2 g/L (high lead group) for 1 year. Our results demonstrated that lead exposure caused autonomic nervous dysfunction, including blood pressure and heart rate increased and heart rate variability (HRV) decreased. Western blotting results indicated that after lead exposure, the protein expression levels in the SG of P2X4 receptor, IL-1β and Cx43 were up-regulated, the phosphorylation of p38 mitogen-activated protein kinase (MAPK) was activated. Real-time PCR results showed that the mRNA expression of P2X4 receptor in the SG was higher in lead exposure group than that in the control group. Double-labeled immunofluorescence results showed that P2X4 receptor was co-expressed with glutamine synthetase (GS), the marker of satellite glial cells (SGCs). These changes were positively correlated with the dose of lead exposure. The up-regulated expression of P2X4 receptor in SGCs of the SG maybe enhance the sympathoexcitatory response induced by chronic lead exposure.

Role of the Immune System in Hypertension

High blood pressure is present in more than one billion adults worldwide and is the most important modifiable risk factor of death resulting from cardiovascular disease. While many factors contribute to the pathogenesis of hypertension, a role of the immune system has been firmly established by a large number of investigations from many laboratories around the world. Immunosuppressive drugs and inhibition of individual cytokines prevent or ameliorate experimental hypertension, and studies in genetically-modified mouse strains have demonstrated that lymphocytes are necessary participants in the development of hypertension and in hypertensive organ injury. Furthermore, immune reactivity may be the driving force of hypertension in autoimmune diseases. Infiltration of immune cells, oxidative stress, and stimulation of the intrarenal angiotensin system are induced by activation of the innate and adaptive immunity. High blood pressure results from the combined effects of inflammation-induced impairment in the pressure natriuresis relationship, dysfunctional vascular relaxation, and overactivity of the sympathetic nervous system. Imbalances between proinflammatory effector responses and anti-inflammatory responses of regulatory T cells to a large extent determine the severity of inflammation. Experimental and human studies have uncovered autoantigens (isoketal-modified proteins and heat shock protein 70) of potential clinical relevance. Further investigations on the immune reactivity in hypertension may result in the identification of new strategies for the treatment of the disease.

Lead Modulates Calcium Entry and Beta-Adrenoceptors Signaling to Produce Myometrial Relaxation in Rats

Modulation of myometrial spontaneity by lead acetate trihydrate (Pb) and its regulatory pathways were studied in estrogenized rats. Isometric tension in myometrial strips under a resting tension of 1 g was measured using data acquisition system-based physiograph and Lab Chart Pro v7.3.7 software. Lead produced a dose-dependent inhibitory effect on rat myometrium with a major effect on phasic contractions compared to tonic contractions along with a reduction in both amplitude and frequency of contraction. Lead (3 μM) significantly (p < 0.05) reduced CaCl2, and 80 mM KDS induced contractile response while potentiated the relaxant effect of phenylephrine. Based on our findings, it may be inferred that lead blocks calcium entry through VDCC and/or stimulates β-adrenoceptors adenylyl cyclase-C-AMP pathway to produce inhibitory effect on rat myometrium.

The impact of subchronic cadmium poisoning on the vascular effect of nitric oxide in rats

The aim of this study was to evaluate the impact of poisoning with cadmium in hypertensive doses (50 or 200 ppm in drinking water for three months) on the basal and stimulated release NO effect in the isolated and perfused rat mesenteric bed. Mesenteric artery preparation preconstricted by norepinephrine (0.5 μg/mL) was used to determine changes in its vascular resistance induced by e-NOS synthase blocker, N-ω-nitro-L-arginine (L-NOARG) injected in increasing doses from 1.0 to 200.0 μg or acetylcholine (ACh) administered in doses from 0.05 × 10-10 to 5.0 × 10-10 mol before and during L-NOARG infusion (1.0 μg/mL). Vascular reactivity was measured as an increase or decrease in perfusion pressure in the constant flow system.

Rats poisoned with 50 or 200 ppm of cadmium demonstrated a significant decrease (P < 0.05) in vascular response to L-NOARG used in doses of 50 or 100 μg. The dose-response curve obtained for L-NOARG was shifted to the right and ED50 value was greater in the group of rats given cadmium in a dose of 200 ppm than in the controls (70.39 ± 10.7 versus 25.79 ± 4.8 μg, P < 0.01). These rats reacted with lower expressed vasodilatation to ACh in doses to 0.2 ± 10-10 mol. In all poisoned rats, L-NOARG enhanced the effect of ACh used in doses from 0.05 to 0.5 ± 10-10 mol, whereas in the control group this effect was only achieved at 0.1 ± 10-10 mol. The serum nitric oxide concentration was decreased (P B < 0.05) in both groups of cadmium-treated rats. These results suggest that cadmium in hypertensive doses modifies the vascular effect of NO in basal conditions and after stimulation by ACh.

Children with health impairments by heavy metals in an e-waste recycling area

E-waste recycling has become a global environmental health issue. Pernicious chemicals escape into the environment due to informal and nonstandard e-waste recycling activities involving manual dismantling, open burning to recover heavy metals and open dumping of residual fractions. Heavy metals derived from electronic waste (e-waste), such as, lead (Pb), cadmium (Cd), chromium (Cr), manganese (Mn), nickel (Ni), mercury (Hg), arsenic (As), copper (Cu), zinc (Zn), aluminum (Al) and cobalt (Co), differ in their chemical composition, reaction properties, distribution, metabolism, excretion and biological transmission. Our previous studies showed that heavy metal exposure have adverse effects on children's health including lower birth weight, lower anogenital distance, lower Apgar scores, lower current weight, lower lung function, lower hepatitis B surface antibody levels, higher prevalence of attention-deficit/hyperactivity disorder, and higher DNA and chromosome damage. Heavy metals influence a number of diverse systems and organs, resulting in both acute and chronic effects on children's health, ranging from minor upper respiratory irritation to chronic respiratory, cardiovascular, nervous, urinary and reproductive disease, as well as aggravation of pre-existing symptoms and disease. These effects of heavy metals on children's health are briefly discussed.

Exposure to a Low Lead Concentration Impairs Contractile Machinery in Rat Cardiac Muscle

Lead exposure has been considered to be a risk factor for hypertension and cardiovascular disease. Our purpose was to evaluate the effects of low plasma lead concentration on cardiac contractility in isolated papillary muscles. Wistar rats were divided in control group or group treated with 100 ppm of lead acetate in the drinking water for 15 days. Blood pressure (BP) was measured weekly. At the end of the treatment period, the animals were anesthetized and euthanized, and parameters related to isolated papillary muscle contractility were recorded. The lead concentrations in the blood reached 12.3 ± 2 μg/dL. The BP was increased in the group treated with 100 ppm of lead acetate. Lead treatment did not alter force and time derivatives of the force of left ventricular papillary muscles. In addition, the inotropic response induced by an increase in the extracellular Ca(2+) concentration was reduced in the Pb(2+) group. However, the uptake of Ca(2+) by the sarcoplasmic reticulum and the protein expression of SERCA and phospholamban remained unchanged. Postrest contraction was similar in the both groups, and tetanic peak and plateau tension were reduced in lead group. These results demonstrated that the reduction in the inotropic response to calcium does not appear to be caused by changes in the trans-sarcolemmal calcium flux but suggest that an impairment of the contractile machinery might be taking place. Our results demonstrate that even at a concentration below the limit considered to be safe, lead exerts deleterious effects on the cardiac contractile machinery.

Withania somnifera ameliorates lead-induced augmentation of adrenergic response in rat portal vein

OBJECTIVES

Present study was undertaken to elucidate the ameliorating potential of Withania somnifera root extract (WRE) against lead-induced augmentation of adrenergic response in rat portal vein.

MATERIALS AND METHODS

In-vitro studies were conducted on effect of lead alone and lead+WRE on rat-isolated portal vein while in-vivo studies were done in three groups of 12 rats each; Group-II and III received 0.5% lead acetate and 1.0% WRE + 0.5% lead acetate, respectively, in drinking water for 12 weeks whereas group-I served as control. Adrenaline and noradrenaline levels in brain and blood were determined by HPLC assay while vascular reactivity of portal vein to lead and WRE was determined by measuring the isometric tension.

RESULTS

Following in-vitro exposure, lead did not alter the contractile effect of phenylephrine. In-vivo studies revealed that contractile effect of lead on portal vein was significantly potentiated and it was antagonized by prazosin (10(-7) M) and WRE (1%). WRE treatment significantly reduced elevated blood noradrenaline (37.80%) and restored noradrenaline level in brain (39.39%) in lead-exposed animals. These values were almost comparable to the control group. But it failed to significantly affect the blood and brain adrenaline levels.

CONCLUSIONS

Results suggest that following pre-exposure of rats to WRE, lead-induced augmentation of alpha 1-adrenoceptors mediated response was reversed possibly by regulating catecholamine release from nerve endings. Thus, WRE may be useful in therapeutic management of lead-induced hypertension.

Combination therapy for the cardiovascular effects of perinatal lead exposure in young and adult rats

Background:

Combination therapy can play a significant role in the amelioration of several toxic effects of lead (Pb) and recovery from associated cardiovascular changes.

Objective:

To investigate the effects of combination therapy on the cardiovascular effects of perinatal lead exposure in young and adult rats

Methods:

Female Wistar rats received drinking water with or without 500 ppm of Pb during pregnancy and lactation. Twenty-two- and 70-day-old rat offspring who were or were not exposed to Pb in the perinatal period received meso-dimercaptosuccinic acid (DMSA), L-arginine, or enalapril and a combination of these compounds for 30 additional days. Noradrenaline response curves were plotted for intact and denuded aortas from 23-, 52-, 70-, and 100-day-old rats stratified by perinatal Pb exposure (exposed/unexposed) and treatment received (treated/untreated).

Results:

Systolic blood pressure was evaluated and shown to be higher in the 23-, 52-, 70-, and 100-day age groups with Pb exposure than in the corresponding control age groups: 117.8 ± 3.9*, 135.2 ± 1.3*, 139.6 ± 1.6*, and 131.7 ± 2.8*, respectively and 107.1 ± 1.8, 118.8 ± 2.1, 126.1 ± 1.1, and 120.5 ± 2.2, respectively (p < 0.05). Increased reactivity to noradrenaline was observed in intact, but not denuded, aortas from 52-, 70-, and 100-day-old exposed rats, and the maximum responses (g of tension) in the respective Pb-exposed and control age groups were as follows: 3.43 ± 0.16*, 4.32 ± 0.18*, and 4.21 ± 0.23*, respectively and 2.38 ± 0.33, 3.37 ± 0.13, and 3.22 ± 0.21, respectively (p < 0.05).

Conclusions:

All treatments reversed the changes in vascular reactivity to noradrenaline in rats perinatally exposed to Pb. The combination therapy resulted in an earlier restoration of blood pressure in Pb-exposed rats compared with the monotherapies, except for enalapril therapy in young rats. These findings represent a new approach to the development of therapeutic protocols for the treatment of Pb-induced hypertension.

Matrix metalloproteinases are involved in cardiovascular diseases

This MiniReview describes the essential biochemical and molecular aspects of matrix metalloproteinases (MMPs) and briefly discusses how they engage in different diseases, with particular emphasis on cardiovascular diseases. There is compelling scientific evidence that many MMPs, especially MMP-2, play important roles in the development of cardiovascular diseases; inhibition of these enzymes is beneficial to many cardiovascular conditions, sometimes precluding or postponing end-organ damage and fatal outcomes. Conducting comprehensive discussions and further studies on how MMPs participate in cardiovascular diseases is important, because inhibition of these enzymes may be an alternative or an adjuvant for current cardiovascular disease therapy.

Blood and urine levels of heavy metal pollutants in female and male patients with coronary artery disease

BACKGROUND

Heavy metal pollutants such as cadmium (Cd), lead (Pb), and mercury (Hg) are rarely the subjects of cardiovascular research although they have been suspected for decades to negatively impact the circulatory system.

METHODS

Apart from detailed anamnestic data, urinary levels of Cd and full blood levels of Pb and Hg were measured in 53 female (mean age: 68.04±7.03 years) and 111 male (mean age: 60.68±11.43 years) nonsmoking or never-smoking patients with angiographically verified and precisely quantified coronary artery disease (CAD).

RESULTS

Although Cd was quantifiable in 68.3% of subjects, only 34.1% of these patients exceeded the critical 1 μg/L Human Biomonitoring (HBM)-I level. Median Pb (20 μg/L) and Hg (0.55 μg/L) levels were lower than the HBM-I, as well as reference levels of Pb. Wine consumption was the main source for Pb, fish and wine consumption for Hg, and previous nicotine abuse for Cd. There was no correlation between Cd, Pb, or Hg and severity of CAD although severity correlated positively with atherosclerosis parameters (uric acid, creatinine, triglycerides, blood urea nitrogen, C-reactive protein) and negatively with high density lipoprotein cholesterol.

CONCLUSION

Cd levels detected in CAD patients were high compared to German and European reference levels but it could not be proven that urine levels of Cd and blood levels of Hg or Pb played a major role in the genesis of CAD, particularly when compared to well-known biomarkers such as blood pressure, glucose, and lipids.

Low-dose chronic lead exposure increases systolic arterial pressure and vascular reactivity of rat aortas

Chronic lead exposure induces hypertension affecting endothelial function. We investigated whether low-concentration lead exposure alters blood pressure and vascular reactivity, focusing on the roles of NO, oxidative stress, cyclooxygenase-derived vasoconstrictor prostanoids, and the local angiotensin-renin system. Aortic rings from 3-month-old Wistar rats were treated daily with lead acetate (first dose 4mg/100g, subsequent doses 0.05mg/100g, im) or vehicle for 30 days. Treatment increased lead blood levels (12μg/dl), blood pressure, and aortic ring contractile response to phenylephrine (1nM-100mM). Contractile response after L-NAME administration increased in both groups but was higher after lead treatment. Lead effects on Rmax decreased more after apocynin and superoxide dismutase administration compared to control. Indomethacin reduced phenylephrine response more after lead treatment than in controls. The selective COX-2 inhibitor NS398, thromboxane A2/prostaglandin H2 receptor antagonist SQ 29,548, TXA2 synthase inhibitor furegrelate, EP1 receptor antagonist SC 19220, and ACE inhibitor and AT1 receptor antagonist losartan reduced phenylephrine responses only in vessels from lead-treated rats. Basal and stimulated NO release was reduced and local O2(-) liberation increased in the lead-treated group compared to controls. eNOS, iNOS, and AT1 receptor protein expression increased with lead exposure, but COX-2 protein expression decreased. This is the first demonstration that blood Pb(2+) (12µg/dl) concentrations below the WHO-established values increased systolic blood pressure and vascular phenylephrine reactivity. This effect was associated with reduced NO bioavailability, increased reactive oxygen species production, increased participation of COX-derived contractile prostanoids, and increased renin-angiotensin system activity.

The Influence of Arsenic, Lead, and Mercury on the Development of Cardiovascular Diseases

As a group, cardiovascular disease (CVD) is the leading cause of death worldwide. It killed twice as many people as infectious and parasitic disease and three times as many people as all forms of cancer. There are other crucial risk factors next to the major risk factors identified by the Framingham Heart Study. In the last few years, detailed studies showed the correlation between environmental pollution and the development of CVD. The question, which environmental toxin is particularly harmful, is answered by CERCLA Priority List of Hazardous Substances with the following toxins: arsenic, lead, and mercury. The effect of these potential toxic metals on the development of cardiovascular diseases includes pathomechanisms as the accumulation of free radicals, damage of endothelial nitric oxide synthase, lipid peroxidation, and endocrine influences. This leads to the damage of vascular endothelium, atherosclerosis, high blood pressure, and an increased mortality from cardiovascular diseases. The cardiovascular effects of arsenic, lead, and mercury exposure and its impact on cardiovascular mortality need to be included in the diagnosis and the treatment of CVD.

Echocardiographic assessment of myocardial function in workers occupationally exposed to lead without clinically evident heart disease

PURPOSE

The aim of the study was to evaluate echocardiographic changes in workers occupationally exposed to low doses of lead.

METHODS

We enrolled 63 men occupationally exposed to lead into the study (group I). Unexposed group consisted of 49 healthy men (group II). Blood lead concentration (Pb-B) and blood zinc protoporphyrin concentration (ZnPP) were determined. Transthoracic echocardiographic examination was performed.

RESULTS

In the studied groups, selected on the criterion of occupational exposure to lead, comparative analysis of echocardiographic parameters indicated statistically significant differences. A negative linear correlations between ZnPP and E' was observed in group I. It was proved that a higher concentration of ZnPP is independent risk factor of lowering the E' mean value in group I.

CONCLUSIONS

Occupational exposure to low doses of lead is associated with the occurrence of discreet morphological and functional heart changes that in the future may predispose to disclosed pathology of heart.

Renin angiotensin system blockade ameliorates lead nephropathy

Lead intoxication is usually insidious and may cause a variety of complications such as kidney damage and hypertension. The role of intrarenal renin-angiotensin system (RAS) in lead-induced nephropathy has not been investigated. Adult male Sprague-Dawley rats were fed with water containing 250ppm of lead acetate (lead group) and deionized water (control group) for 4weeks. Another two groups started to receive intraperitoneal captopril (50mg/kg/d) or losartan (10mg/kg/d) after 2weeks of lead feeding and continued for another 2weeks. Immunoblotting was used to analyze the protein amount of intrarenal RAS components and transforming growth factor-beta (TGF-β). Compared with control group, lead exposure resulted in increased proteinuria after 2-week treatment (4.2±0.9mg/100g vs. 1.8±0.8mg/100g, p<0.05) and 4-week (5.2±1.7mg/100g, p<0.05). Serum creatinine level was increased (0.40±0.2 vs. 0.3 ±.04mg/dL, p<0.05) and calculated glomerular filtration rate (GFR) was decreased (2.68±1.03 vs. 3.37±0.11mL/min, p<0.05). Intrarenal angiotensin converting enzyme (ACE), angiotensin II (ANG II), angiotensin II type 1 receptor (AT1R) and transforming growth factor-beta (TGF-β) were upregulated in lead group. Captopril and losartan administration reduced proteinuria significantly (3.0±0.50mg/100g of captopril and 2.7±0.4mg/100g of losartan group) and lowered systolic blood pressure when compared with lead group. Furthermore, serum creatinine levels and GFR were improved by RAS blockade. Captopril treatment significantly reduced protein abundance of ACE, ANG II, AT1R and TGF-β. Losartan treatment also decreased ANG II and TGF-β. We concluded that lead exposure elicited intrarenal RAS activation with associated proteinuria and impaired renal function. RAS blockade was effective in alleviating lead-associated kidney injury and lowering blood pressure.

Heart function in magnetic resonance imaging and the mesenteric artery reactivity in rats receiving lead-contaminated drinking water

The aim of this study was to evaluate the effect of lead (Pb)-contaminated drinking water on magnetic resonance imaging (MRI)-estimated cardiac function, vascular reactivity, and serum lipids in rats. For 3 months, male Wistar rats, aged 4–6 weeks, were given drinking water with the addition of lead acetate at a concentration of 100 ppm Pb (10 rats) or water free from Pb (8 control rats). The cardiac MRI was performed at rest and under β-adrenergic stimulation on a 4.7 T scanner using electrocardiogram-triggered gradient echo (FLASH) cine sequence. After 1–2 weeks of the MRI test, experiments were performed ex vivo. After stabilization of perfusion pressure (PP), norepinephrine at doses from 0.01 to 5.0 μg was dissolved in Krebs solution, injected in a volume of 100 μl, and next infused at a concentration of 0.5 μg/ml into the isolated mesenteric artery. In this manner, preconstricted mesenteric bed was used to determine PP changes induced by acetylcholine, given at doses from 0.05 to 5.0 μg, before and during the infusion of nitric oxide synthase inhibitor (1.0 μg/ml). At the end, dobutamine (5 mg), followed by potassium chloride (10.5 mg), was injected. Lipid levels were determined enzymatically, blood Pb level was measured by the atomic absorption spectrophotometer. This study showed that Pb impairs the left ventricular systolic and diastolic function. Pb-induced changes in response to resistance of vessels to vasoactive agents may be secondary to the reduced left ventricular ejection fraction. The high-density lipoprotein subfraction 2 (HDL2) is involved in the cardiovascular effect of Pb.

Ischemic heart disease risk factors in lead exposed workers: research study

Background

Review of other epidemiological studies reveal inconsistent results of relationships between high blood lead level and risk of hypertension, hyperlipidemia and hyperglycemia. In this study we wanted to find if there is a relationship between blood lead level and these ischemic heart disease risk factors.

Methods

This cross-sectional study was conducted in a battery recycling plant, and 497 male workers with the mean age of 41.7 (±6.50) years were recruited from all over the plant (those from the products and maintenance sections were classed as “high lead exposed group” and those from amongst the office, laboratory, security services and food services sections as “low lead exposed group”). Personal information such as demographics and work history was obtained through a questionnaire.

Mean (±Standard deviation) for quantitative variables, Frequency (Percent) for qualitative variables, and Odd’s ratio (OR) with 95% confidence interval (95% CI) for estimating the effect of blood lead level on lipid profile[triglyceride (TG), cholesterol(CHOL), low density lipoprotein – Cholesterol(LDL-C),high density lipoprotein –Cholesterol(HDL-C)], hypertension(HTN) and fasting blood sugar (FBS) level. Logistic regression modeling was used for multivariate analysis and adjusting the effect of different variables (age, body mass index(BMI), eating habits, cigarette smoking).

Results

The mean Blood Lead Level (BLL) was >40 μg/dl in 281 (56.6%) subjects, ≤40 μg in 216 (43.4%) subjects and the mean BLL was 43.3 μg/dl (n = 497). The mean job experience involving lead exposure was 13 years. There was no significant correlation between BLL and FBS (p = 0.68), between BLL and TG (P = 0.32), between BLL and HDL-C (p = 0.49), between BLL and LDL-C (p = 0.17), between BLL and CHOL(p = 0.96), between BLL and systolic blood pressure (p = 0.12). The adjusted Odd’s ratio for the effect of BLL >40.0 μg/dl on diastolic blood pressure was1.03 (95% CI: 1.01–1.05) with p = 0.05.

Conclusion

This study showed an association of high BLL with diastolic blood pressure but not with TG, FBS, and HDL-C, LDL-C and CHOL . This result persisted even after adjustment was made for age, BMI and job experience, smoking and eating habits. Attention to health-protective policies, individual behavioral changes and regular periodic medical examination with focus on diastolic blood pressure in lead exposed workers is likely to decrease the public health burden of ischemic heart disease.

Acute exposure to lead increases myocardial contractility independent of hypertension development

We studied the effects of the acute administration of small doses of lead over time on hemodynamic parameters in anesthetized rats to determine if myocardial contractility changes are dependent or not on the development of hypertension. Male Wistar rats received 320 µg/kg lead acetate iv once, and their hemodynamic parameters were measured for 2 h. Cardiac contractility was evaluated in vitro using left ventricular papillary muscles as were Na+,K+-ATPase and myosin Ca2+-ATPase activities. Lead increased left- (control: 112 ± 3.7 vs lead: 129 ± 3.2 mmHg) and right-ventricular systolic pressures (control: 28 ± 1.2 vs lead: 34 ± 1.2 mmHg) significantly without modifying heart rate. Papillary muscles were exposed to 8 µM lead acetate and evaluated 60 min later. Isometric contractions increased (control: 0.546 ± 0.07 vs lead: 0.608 ± 0.06 g/mg) and time to peak tension decreased (control: 268 ± 13 vs lead: 227 ± 5.58 ms), but relaxation time was unchanged. Post-pause potentiation was similar between groups (n = 6 per group), suggesting no change in sarcoplasmic reticulum activity, evaluated indirectly by this protocol. After 1-h exposure to lead acetate, the papillary muscles became hyperactive in response to a β-adrenergic agonist (10 µM isoproterenol). In addition, post-rest contractions decreased, suggesting a reduction in sarcolemmal calcium influx. The heart samples treated with 8 µM lead acetate presented increased Na+,K+-ATPase (approximately 140%, P < 0.05 for control vs lead) and myosin ATPase (approximately 30%, P < 0.05 for control vs lead) activity. Our results indicated that acute exposure to low lead concentrations produces direct positive inotropic and lusitropic effects on myocardial contractility and increases the right and left ventricular systolic pressure, thus potentially contributing to the early development of hypertension.

Acute lead exposure increases arterial pressure: role of the renin-angiotensin system

Background

Chronic lead exposure causes hypertension and cardiovascular disease. Our purpose was to evaluate the effects of acute exposure to lead on arterial pressure and elucidate the early mechanisms involved in the development of lead-induced hypertension.

Methodology/Principal Findings

Wistar rats were treated with lead acetate (i.v. bolus dose of 320 µg/Kg), and systolic arterial pressure, diastolic arterial pressure and heart rate were measured during 120 min. An increase in arterial pressure was found, and potential roles of the renin-angiotensin system, Na⁺,K⁺-ATPase and the autonomic reflexes in this change in the increase of arterial pressure found were evaluated. In anesthetized rats, lead exposure: 1) produced blood lead levels of 37±1.7 µg/dL, which is below the reference blood concentration (60 µg/dL); 2) increased systolic arterial pressure (Ct: 109±3 mmHg vs Pb: 120±4 mmHg); 3) increased ACE activity (27% compared to Ct) and Na⁺,K⁺-ATPase activity (125% compared to Ct); and 4) did not change the protein expression of the α1-subunit of Na⁺,K⁺-ATPase, AT₁ and AT₂. Pre-treatment with an AT₁ receptor blocker (losartan, 10 mg/Kg) or an ACE inhibitor (enalapril, 5 mg/Kg) blocked the lead-induced increase of arterial pressure. However, a ganglionic blockade (hexamethonium, 20 mg/Kg) did not prevent lead's hypertensive effect.

Conclusion

Acute exposure to lead below the reference blood concentration increases systolic arterial pressure by increasing angiotensin II levels due to ACE activation. These findings offer further evidence that acute exposure to lead can trigger early mechanisms of hypertension development and might be an environmental risk factor for cardiovascular disease.

Mechanisms of lead-induced hypertension and cardiovascular disease

Lead is a ubiquitous environmental toxin that is capable of causing numerous acute and chronic illnesses. Population studies have demonstrated a link between lead exposure and subsequent development of hypertension (HTN) and cardiovascular disease. In vivo and in vitro studies have shown that chronic lead exposure causes HTN and cardiovascular disease by promoting oxidative stress, limiting nitric oxide availability, impairing nitric oxide signaling, augmenting adrenergic activity, increasing endothelin production, altering the renin-angiotensin system, raising vasoconstrictor prostaglandins, lowering vasodilator prostaglandins, promoting inflammation, disturbing vascular smooth muscle Ca(2+) signaling, diminishing endothelium-dependent vasorelaxation, and modifying the vascular response to vasoactive agonists. Moreover, lead has been shown to cause endothelial injury, impede endothelial repair, inhibit angiogenesis, reduce endothelial cell growth, suppress proteoglycan production, stimulate vascular smooth muscle cell proliferation and phenotypic transformation, reduce tissue plasminogen activator, and raise plasminogen activator inhibitor-1 production. Via these and other actions, lead exposure causes HTN and promotes arteriosclerosis, atherosclerosis, thrombosis, and cardiovascular disease. In conclusion, studies performed in experimental animals, isolated tissues, and cultured cells have provided compelling evidence that chronic exposure to low levels of lead can cause HTN, endothelial injury/dysfunction, arteriosclerosis, and cardiovascular disease. More importantly, these studies have elucidated the cellular and molecular mechanisms of lead's action on cardiovascular/renal systems, a task that is impossible to accomplish using clinical and epidemiological investigations alone.

The vascular system as a target of metal toxicity

Vascular system function involves complex interactions among the vascular endothelium, smooth muscle, the immune system, and the nervous system. The toxic metals cadmium (Cd), arsenic (As), and lead (Pb) can target the vascular system in a variety of ways, ranging from hemorrhagic injury to subtle pathogenic remodeling and metabolic changes. Acute Cd exposure results in hemorrhagic injury to the testis, although some strains of animals are resistant to this effect. A comparison of Cd-sensitive with Cd-resistant mouse strains showed that expression of the Slc39a8 gene, encoding the ZIP8 transporter, in the testis vasculature endothelium is responsible for this difference. Endogenously, ZIP8 is a Mn(2+)/HCO(3)(-)symporter that may also contribute to Cd damage in the kidney. Chronic Cd exposure is associated with various cardiovascular disorders such as hypertension and cardiomyopathy and it is reported to have both carcinogenic and anticarcinogenic activities. At noncytotoxic concentrations of 10-100nM, Cd can inhibit chemotaxis and tube formation of vascular endothelial cells. These angiostatic effects may be mediated through disruption of vascular endothelial cadherin, a Ca(2+)-dependent cell adhesion molecule. With regard to As, ingestion of water containing disease-promoting concentrations of As promotes capillarization of the liver sinusoidal endothelium. Because capillarization is a hallmark precursor for liver fibrosis and contributes to an imbalance of lipid metabolism, this As effect on hepatic endothelial cells may be a pathogenic mechanism underlying As-related vascular diseases. With regard to Pb, perinatal exposure may cause sustained elevations in adult blood pressure, and genetically susceptible animals may show enhanced sensitivity to this effect. Taken together, these data indicate that the vascular system is a critical target of metal toxicity and that actions of metals on the vascular system may play important roles in mediating the pathophysiologic effects of metals in specific target organs.

Perinatal lead exposure affects nitric oxide and cyclooxygenase pathways in aorta of weaned rats

Perinatal Pb exposure may modulate arterial tone through nitric oxide (NO) and cyclooxygenase products. To investigate this, Wistar dams received 1000 ppm of Pb or sodium acetate (control) in drinking water during pregnancy and lactation. Curves were constructed in phenylephrine-precontracted intact and/or denuded rings of thoracic aortas of weaned (23-day-old) male pups from their responses to N(omega)-nitro-L-arginine methyl ester (L-NAME, NO synthase inhibitor) and ACh in the absence or presence of indomethacin (10(-5)M, cyclooxygenase inhibitor) or L-NAME (3 x 10(-7)M and 3 x 10(-4)M). Blood lead concentration and systolic blood pressure (SBP) were higher in intoxicated than control pups (blood lead microg/dl: control < 3.0, Pb 58.7 +/- 6.5*; SBP mmHg: control 111.4 +/- 2.3, Pb 135.5 +/- 2.4*). In L-NAME-treated rings maximal responses increased in Pb-exposed rats, and were higher in intact than in denuded aortas (contraction [% of phenylephrine] intact: control 184.3 +/- 23.7, Pb 289.1 +/- 18.3*; denuded: control 125.1 +/- 4.5, Pb 154.8 +/- 13.3*). ACh-induced relaxation in intact aortas from Pb-exposed rats presented rightward shift in L-NAME presence (EC50 x 10(-7)M: control 1.32 [0.33-5.18], Pb 4.88 [3.56-6.69]*) but moved left under indomethacin (EC50 x 10(-7)M: control 8.95 [3.47-23.07], Pb 0.97 [0.38-2.43]*). *p < 0.05 significant relative to the respective control; N = 7-9. Endothelium removal abolished ACh-induced relaxation. Perinatal Pb exposure caused hypertension associated with alterations in the production and/or release of basal and stimulated endothelium-derived relaxing factors-NO and constricting cyclooxygenase products. These findings may help explain the contribution of NO and cyclooxygenase products to the etiology and/or maintenance of Pb-induced hypertension and could ultimately lead to therapeutic advantages in plumbism.

Mycophenolate mofetil administration reduces renal inflammation, oxidative stress, and arterial pressure in rats with lead-induced hypertension

Hypertension is a likely consequence of chronic lead exposure in humans, especially in association with reduced renal function and in high risk populations. Numerous studies have demonstrated that oxidative stress plays an important role in the pathogenesis of experimental lead-induced hypertension and we have shown recently that tubulointerstitial immune cell infiltration is a feature of chronic low-dose lead exposure. Since oxidative stress, renal inflammation, and angiotensin activity are closely linked characteristics in experimental models of hypertension, we decided to investigate whether lead-induced hypertension would be ameliorated by suppressing renal inflammation with the immunosuppressive drug mycophenolate mofetil (MMF). We studied rats exposed for 14 wk to lead acetate (100 ppm in the drinking water) that, in addition, received either MMF, 20 mg.kg(-1).day(-1) by gastric gavage (Pb.MMF group, n = 12) or vehicle (Pb group, n = 12). Control rats received MMF alone (n = 5) or neither lead nor MMF (n = 6). All rats were killed at the end of the experiment. Low-dose lead exposure resulted in mild to moderate tubular cell damage and a progressive increment in blood pressure, oxidative stress, interstitial accumulation of lymphocytes and macrophages, NF-kappaB activation, and increased renal angiotensin II level. The administration of MMF suppressed the tubulointerstitial accumulation of lymphocytes and macrophages and prevented the hypertension, oxidative stress, and NF-kappaB activation and reduced the heightened renal angiotensin content associated with chronic lead exposure. We conclude that interstitial inflammation plays an important role in lead-induced hypertension.

Dietary Calcium as a Potential Modifier of the Relationship of Lead Burden to Blood Pressure

BACKGROUND

Cumulative lead burden and low dietary calcium have been independently associated with increased risk of hypertension. There is evidence of an interaction between these factors. We tested the hypothesis that dietary calcium intake modifies the relationship between lead burden and hypertension.

METHODS

A total of 471 men from the Normative Aging Study were evaluated. Bone lead was assessed using a K-x-ray fluorescence instrument, and information on dietary calcium intake was obtained with a self-administered semiquantitative food frequency questionnaire.

RESULTS

We categorized 259 subjects (55%) as having low calcium intake (< or =800 mg/d) and 212 subjects (45%) as having higher calcium intake. In logistic regression models stratified by dietary calcium intake, tibia lead had a weak association with hypertension among subjects with low dietary calcium (odds ratio for 1-standard deviation increase in tibia lead = 1.30; 95% confidence interval = 0.97-1.74) but not in subjects with higher dietary calcium intake. Similarly, blood lead was associated with hypertension only in subjects with low calcium intake. We also found evidence of an interaction between dietary calcium intake and body mass index.

CONCLUSIONS

High bone and blood lead increased the likelihood of hypertension, particularly among subjects with low dietary calcium intake. Dietary calcium may be helpful in prevention of hypertension induced by elevated lead burden.

Effects of short-term and subchronic lead poisoning on nitric oxide methabolites and vascular responsiveness in rat

Chronic exposure to low levels of lead results in sustained hypertension in humans and experimental animals. The mechanism of lead-induced hypertension remains unclear. We investigated the short-term (4 and 8 weeks) and subchronic (12 weeks) effects of lead treatment on responsiveness of vascular adrenergic system and level of nitric oxide metabolites, that is, total nitrates and nitrites (NOx). Male Sprague-Dawley rats were treated with lead acetate (100 ppm in drinking water) for 12 weeks. Short-term lead administration resulted in marked elevation of blood pressure accompanied by significant reduction in serum NOx levels. In contrast, after subchronic lead administration the trend of decrease in NOx levels somehow reversed despite further increase in blood pressure. Both short-term and subchronic lead administration resulted in significant differences in vascular reactivity with respect to either vasoconstrictor (phenylephrine and clonidine) or vasodilator (isoproterenol) agents. We conclude that vascular adrenergic system and nitric oxide pathway change in short-term and subchronic phases of lead poisoning.

Lipids, lipid peroxidation and 7-ketocholesterol in workers exposed to lead

The study population included healthy men and hypertensive employees of zinc and lead steelworks in the south of Poland. Workers exposed to lead (n=137) were divided into two groups: the first included employees with low exposure to lead (LL) with mean blood lead (PbB) 25-40 microg/dL and the second one with PbB over 40 microg/dL (HL group). The administration workers (n=35) were the control group. Evaluation of lipids and oxidative changes of cholesterol and lipids were estimated in blood samples. No significant changes in concentration of 7-ketocholesterol and blood lipids (cholesterol, HDL, LDL, triglycerides) were found. Lipid peroxidation (LP) was significantly higher in both exposed groups in plasma and in the HL group in erythrocytes when compared with control. There can be two independent sources of LP increase: the first is connected with the direct effect of lead's ions on erythrocytes, the second is the prooxidative effect of delta-aminolevulinic acid. Hypertension in the HL group when compared with people with PbB below 40 microg/dL (OR 4.4, 95%CI 1.4-14.5) was found more often. LP significantly increased by about 71% and concentration of 7-ketocholesterol by about 122% in hypertensives when compared with normotensives in the HL group.

Evaluation of peripheral blood neutrophil leucocytes in lead-exposed workers

BACKGROUND

Inorganic lead can interfere with humoral and especially cell-mediated immunity even at frequently occurring (<50 microg/dl) blood lead (Pb-B) levels. Occupational exposure to lead causes a primary impairment of the chemotactic and phagocytic activities of neutrophil leucocytes.

OBJECTIVE

To verify whether, after taking into account the main confounding factors, occupational lead exposure is shown to induce changes in the number of blood neutrophil leucocytes, and to assess a possible dose-response relationship between Pb-B and the circulating neutrophil count in exposed workers.

SUBJECTS AND METHODS

The study included 68 male lead-exposed (E) workers and 59 male workers in a food plant, recruited as controls (NE). A standardized questionnaire probing work, social, familial and personal medical history was administered to all the subjects. Blood and urine samples were collected to determine the dose and effect biological indices of lead and the total white blood cell and neutrophil counts.

RESULTS

Pb-B levels were significantly higher in E (geometric mean (GM): 20.5 microg/dl; 3.2-120 microg/dl) than in NE workers (GM: 3.5 microg/dl; 1-11 microg/dl). The mean absolute neutrophil count (ANC) was significantly higher in E workers with respect to NE workers. ANC correlated significantly with the biological lead dose and effect indices. Moreover, there was a dose-dependent increase of ANC with increasing Pb-B levels. The linear relationship between ANC and Pb-B was confirmed even after correction for age, body mass index and smoking habit. We also found an interaction between Pb-B level and smoking habit in increasing the number of blood neutrophils in lead-exposed workers.

CONCLUSION

Our study is the first to describe a dose-dependent effect of lead on ANC in exposed workers. Our results underline the importance of promoting a further reduction of occupational lead exposure levels, adopting adequate individual protection means, as well as conducting medical campaigns against smoking, at the workplace.

Plasma lipid profiles and risk of cardiovascular disease in occupational lead exposure in Abeokuta, Nigeria

In order to investigate the effects of lead exposure on risk of cardiovascular disease during occupational exposure to this metal, plasma cholesterol and its fractions as high-density liporotein (HDL), low-density liporotein (LDL) and triglyceride were determined in various artisans in Abeokuta, Nigeria who have been shown to be occupationally exposed to lead and these were related to blood lead levels. Increased risk of cardiovascular disease was observed in the artisans. Total cholesterol in the artisans was between 1.5 and 2.0 times higher in the artisans than that present in controls while LDL cholesterol was between 1.6 and 2.4 times higher in the artisans when compared with control subjects [p < 0.001]. HDL cholesterol and triglyceride levels were not affected [p > 0.05]. A significant positive correlation was observed between blood lead and total cholesterol on one hand [r = 0.372; p = 3.0 × 10^-5] and blood lead and LDL cholesterol on the other hand [r = 0.283; p = 0.001]. LDL/HDL cholesterol ratio was also higher in the artisans when compared with control. Blood pressure (systolic and diastolic) and other anthropometric parameters were not significantly different between the artisans and the control subjects [p > 0.05]. Results suggest that lead exposure increases cholesterol synthesis and transport to peripheral tissues whereas reverse cholesterol transport to the liver is not affected.

Chronic exposure to low doses of lead results in renal infiltration of immune cells, NF-kappaB activation, and overexpression of tubulointerstitial angiotensin II

Chronic exposure to low doses of lead results in generation of reactive oxygen species, reduced nitric oxide availability, and arterial hypertension. The present studies were done to define if other conditions associated with oxidative stress, such as renal interstitial inflammation, nuclear factor-kappaB (NF-kappaB) activation, and cells expressing angiotensin II, are, in fact, features of low-dose lead exposure. Male Sprague-Dawley rats were randomly assigned to the lead group (n = 8) or the control group (n = 9). The lead group received 100 ppm lead acetate in the drinking water for 14 weeks. At the end of this period of time, rats were killed under general anesthesia, and the kidneys were harvested for studies. The lead-exposed group presented focal tubulointerstitial damage and highly significant increments in nitrotyrosine immune staining, lymphocyte and macrophage infiltration, angiotensin II-positive cells, and intranuclear positive staining for the p65 DNA-binding subunit of NF-kappaB in tubulointerstitial cells. Tubulointerstitial inflammation, cells expressing angiotensin II, and NF-kappaB activation are consequences of a 3-month low-dose exposure to lead and likely play a role in the development of hypertension and chronic lead nephropathy.

The change of beta-adrenergic system after cessation of lead exposure

For understanding a reversible or irreversible harm of beta-adrenergic system in lead induced cardiovascular disease (hypertension), We set up animal model to estimate the change of blood pressure and sympathetic nervous system after lead exposure withdrawn in the study. We address three topics in this study: (a) the relationship between withdrawal time of lead exposure and beta-adrenergic receptor, plasma catecholamine level, blood pressure, and lead level in heart, aorta, and kidney in lead-induced hypertensive rats after lead exposure stopped; (b) the relationship between blood pressure and beta-adrenergic receptor in heart, aorta, and kidney; (c) the estimation of relationship between lead withdrawn and the variation of beta-adrenergic system. Wistar rats were chronically fed with 2% lead acetate (experimental group) and water (control group) for 2 months. The rats were divided into 8 groups by withdrawal time of lead exposure stopped. Plasma catecholamine level was measured by high-performance liquid chromatography. Radioligand binding assay was measured by a method that fulfilled strict criteria of beta-adrenergic receptor using the ligand [125I]iodocyanopindolol. The levels of lead were determined by electrothermal atomic absorption spectrometry. The results showed that a close relation between reduced lead level and the plasma catecholamine level decreased, aorta beta-adrenergic receptor increased, kidney beta-adrenergic receptor diminished, heart beta-adrenergic receptor increased, and blood pressure dropped after lead exposure withdrawn. The study on the regulation of beta-adrenergic system in lead-induced hypertension after lead withdrawn might also provide insight about the nature of this disease state.

The impact of subchronic lead poisoning on the vascular effect of nitric oxide in rats

Lead-induced arterial hypertension is suggested to have resulted mainly from a reduction in nitric oxide (NO) bioactivity in vessel walls. The aim of this study was to evaluate the impact of poisoning by lead in so-called hypertensive doses on the basal and stimulated released NO effect in the rat mesenteric bed. Male Buffalo rats were given lead in a dose of 50 or 100ppm in drinking water for three months. The isolated mesenteric bed preconstricted by norepinephrine (0.5μg/ml) was used to determine the changes in vascular resistance induced by N-ω-nitro-l-arginine injected in increasing doses from 1.0 to 200.0μg or by acetylcholine administered in doses from 0.05 × 10(-10) to 5.0 × 10(-10)mol. These changes were measured as an increase or decrease in perfusion pressure in the constant flow system. In comparison with controls rats given 50ppm of lead, an increase in maximal response to N-ω-nitro-l-arginine (P < 0.01) and acetylcholine (P < 0.05) and a shift to the left of the dose-response curve for acetylcholine were demonstrated. Vascular responses in rats, who were given 100ppm of lead, were similar to those observed in the control group. It is concluded that lead induces NO-mediated changes of vascular tone and vascular reactivity only in the small range of doses known as hypertensive.

Lead-induced hypertension: role of oxidative stress

Chronic, low-level lead exposure causes hypertension in both animals and humans. The pathogenesis of lead-induced hypertension is multifactorial, including such diverse mechanisms as: inactivation of endogenous nitric oxide and downregulation of soluble guanylate cyclase by reactive oxygen species (ROS), leading to a functional deficiency in nitric oxide; heightened sympathetic activity and plasma norepinephrine together with depressed vascular and elevated renal beta-adrenergic receptor density; elevated plasma angiotensin-converting enzyme (ACE) activity, plasma renin activity (PRA), angiotensin II (Ang-II), and aldosterone levels; increased kininase I and kininase II activities; lead-induced inhibition of vascular smooth muscle Na(+)-K+ ATPase, leading to a rise in cellular Na+ and, hence, Ca2+; and a possible rise in endothelin and thromboxane generation. In this article, we present an overview of the epidemiology and proposed underlying mechanisms of lead-induced hypertension.

Investigation of circulatory and tissue ACE activity during development of lead-induced hypertension

Prolonged exposure to low levels of lead causes systemic hypertension. Several mechanisms have been proposed to explain lead-induced hypertension. Recently, the etiological role of the renin-angiotensin system (RAS) has been investigated in this context. This study assessed the alterations of circulatory and tissue angiotensin converting enzyme (ACE) activity during development of lead induced hypertension. Male rats were divided to two main groups: lead-treated animals which received lead acetate, 100 ppm, in drinking water for 2, 4, 6, and 8 weeks and a control group given distilled water. The ACE activity in serum and tissues was analyzed by HPLC. The blood pressure gradually increased in correlation with lead exposure with time. The study also revealed significant elevation of local and serum ACE activity in the early phase of lead treatment; however, chronic lead exposure suppressed ACE activity in serum and tissues. These results emphasize the etiological role of ACE activity in the early phase of lead-induced hypertension.

Beta-adrenergic receptor density and adenylate cyclase activity in lead-exposed rat brain after cessation of lead exposure

To understanding the reversible or irreversible harm to the beta-adrenergic system in the brain of lead-exposed rats, this study sets up an animal model to estimate the change in the sympathetic nervous system of brain after lead exposure was withdrawn. We address the following topics in this study: (a) the relationship between withdrawal time of lead exposure and brain beta-adrenergic receptor, blood lead level, and brain lead level in lead-exposed rats after lead exposure was stopped; and (b) the relationship between lead level and beta-adrenergic receptor and cyclic AMP (c-AMP) in brain. Wistar rats were chronically fed with 2% lead acetate and water for 2 months. Radioligand binding was assayed by a method that fulfilled strict criteria of beta-adrenergic receptor using the ligand [125I]iodocyanopindolol. The levels of lead were determined by electrothermal atomic absorption spectrometry. The c-AMP level was determined by radioimmunoassay. The results showed a close relationship between decreasing lead levels and increasing numbers of brain beta-adrenergic receptors and brain adenylate cyclase activity after lead exposure was withdrawn. The effect of lead exposure on the beta-adrenergic system of the brain is a partly reversible condition.