Nephrotoxicity of cadmium & lead

Cadmium and lead are divalent cations with a propensity to settle in the proximal tubule of the nephron, leading to nephrotoxicity. The pathophysiological results, however, tend to diverge. Cadmium in sufficient cumulative dosage leads to the production of the Fanconi syndrome, a generalized proximal tubular reabsorptive defect thought to be related to inhibition of both ATP production and Na-K-ATPase activity. On the other hand, lead accumulation in the proximal tubule leads to hyperuricaemia and gout, presumably by inhibiting uric acid secretion, and diminished glomerular filteration rate (GFR). Fanconi syndrome is seen unusually only in children and experimental animals. Cadmium nephrotoxicity is heralded by increased excretion of beta2-microglobulin, retinol binding protein and alpha1-microglobulin, indicative of decreased proximal tubule function. Beta2-microglobulinuria is not found in lead nephropathy. In lead nephropathy albuminuria is absent or minimal whereas in cadmium nephropathy albuminuria is variable. From the standpoint of pathology, both entities are characterized by tubulointerstitial disease and fibrosis, but only early lead nephropathy is characterized by the presence of proximal tubule nuclear inclusion bodies, due to the combination of lead with a lead binding-protein.

Cardiovascular effects of lead exposure

Several epidemiological and clinical studies have found a link between chronic lead exposure and elevated blood pressure. In addition, a few population studies have shown possible connection between lead exposure and other cardiovascular disorders including ischaemic coronary heart disease, cerebrovascular accidents, and peripheral vascular disease. The causal link between chronic lead exposure and hypertension (HTN) has been confirmed by several studies in experimental animals. In addition, the effects of lead on the heart and vascular function have been explored in a limited number of in vivo and in vitro studies. The in vivo, ex vivo and in vitro studies conducted in laboratory animal, cultured cells and isolated tissues have helped to elucidate many of the mechanisms by which lead exposure can cause HTN and cardiovascular disease. This review is intended to provide an overview of the epidemiology and the underlying mechanisms of lead-associated HTN and cardiovascular disease.

Is lead exposure the principal cause of essential hypertension?

Lead is a ubiquitous toxin, known to have adverse effects on the body even at low levels of exposure. In this review we explore whether low lead may be the principal or a major contributory cause of essential hypertension, and whether removal of lead from the environment may eventually reduce both the overall incidence of hypertension and the increased incidence with aging.

Influence of lead on rat thoracic aorta contraction and relaxation

Low levels of lead, but not high levels, produce hypertension. This mystery has not yet been resolved. In this study we compared the in vitro vasoresponsiveness in rat thoracic aorta to low dose (10(-8) mol/L) and high dose (10(-5) mol/L and 10(-4) mol/L) lead acetate. In addition to the direct response to lead, we examined reactivity to norepinephrine, acetylcholine, isoproterenol, phorbol ester, and calcium in the presence and absence of lead. Neither low-dose nor high-dose lead directly affected aortic contractile or relaxant responses. However, lead, only at the highest concentration (10(-4) mol/L), increased the contractions to calcium at all submaximal calcium concentrations. We conclude that low-dose lead must increase blood pressure indirectly through a humoral effect. The reasons for the failure of high-dose lead to influence blood pressure remain to be explored.

Lead-induced hypertension. III. Increased hydroxyl radical production

Lead-induced hypertension has previously been shown to be closely associated with an increase in reactive oxygen species in low lead (100 ppm)-treated rats. The present study has attempted to define the specific moiety involved by noting the blood pressure (BP), reactive oxygen species (MDA-TBA), hydroxyl radical, and nitrotyrosine responses to infusion of the reactive oxygen species scavenger dimethylthiourea. Dimethylthiourea, a reputed scavenger of hydroxyl radical, normalized BP and MDA-TBA in the lead-treated rats but had no effect in normal control animals. MDA-TBA, hydroxyl radical, and nitrotyrosine, the tissue end product of peroxynitrite, were reduced to or toward normal by dimethylthiourea. The results, therefore, are consistent with the suggestion that either hydroxyl radical or peroxynitrite may be the reactive species affected by lead.

Lead promotes hydroxyl radical generation and lipid peroxidation in cultured aortic endothelial cells

Early studies by our group have shown that lead-induced hypertension (HTN) is closely related to enhanced activity of reactive oxygen species (ROS). In addition, we have found indirect evidence that hydroxyl radical may be the most likely culprit in lead-exposed animals. In the present study, rat aortic endothelial cells were incubated in the presence of 0, 0.01, 0.1, 0.5, and 1.0 ppm lead acetate for 1, 24, and 48 h. At the conclusion of the incubation period cells were harvested and the media were collected. Lipid peroxidation products were measured as malondialdehyde-thiobarbituric acid (MDA-TBA) in the medium and hydroxyl radical was measured as 2,3-dihydroxybenzoic acid (2,3 DHBA) in the cells. After exposure to lead for 48 h, MDA-TBA generation and 2,3 DHBA formation were significantly increased. These data clearly demonstrate that lead exposure promotes hydroxyl radical generation and induces oxidative stress in isolated endothelial cells, mimicking the effects observed in lead-exposed animals. Enhanced inactivation of endothelium-derived nitric oxide by locally produced oxygen free radicals could contribute to endothelial dysfunction and HTN in lead-exposed animals.

Severe lead-induced peripheral neuropathy in a dialysis patient

Toxic neuropathy caused by lead (manifested as wrist drop) was a frequent phenomenon before 1925. In modern times, it is a distinct rarity. We report herein a Hispanic woman who developed end-stage renal failure, followed by wrist drop, in whom the maximal total blood lead was 69 microg/dL. Measurements of lead in her tibia and calcaneus by K-x-ray fluorescence, however, showed markedly elevated values. The wrist drop cleared after four treatments with intravenous calcium sodium edetate (Ca EDTA). In vitro studies of (210)Pb uptake by red blood cells (RBC) after incubation with normal or uremic plasma indicated that (210)Pb uptake was inhibited by uremic plasma. These studies suggest the presence of a transport inhibitor in uremia that modifies the distribution of lead between plasma and RBC, leading to lower overall blood values.

Adequate dietary calcium mitigates osteopenia induced by chronic lead exposure in adult rats

The purpose of the present study was to investigate bone changes in the adult rat exposed to low lead levels during intake of normal dietary calcium and to contrast these findings with data from our earlier studies performed with animals receiving low dietary calcium concurrent with lead exposure. The present study exposed adult rats to 100 ppm lead via drinking water for 12 weeks and assessed bone histology, 1,25-dihydroxyvitamin D, 25(OH)vitamin D and parathyroid hormone levels. No osteopenia was evident by quantitative bone histology, and circulating levels of 1,25-dihydroxyvitamin D, 25(OH) vitamin D and parathyroid hormone were normal. Bone ash findings documented incorporation of significant amounts of lead into bone mineral. These findings document absence of interference with vitamin D metabolism, absence of secondary hyperparathyroidism and absence of osteopenia following 12 weeks of low lead exposure in the adult rat maintained on normal calcium intake. Results stress the importance of adequate calcium intake in our elderly population who may be exposed to cumulative, low-level lead exposure.

Na-K-ATPase inhibitor dissociated from hypertension-associated plasma protein

It has been demonstrated that human plasma contains a low molecular weight sodium-potassium-stimulated adenosine triphosphatase (Na-K-ATPase) inhibitor, which can be dissociated from a circulating protein with a molecular weight of approximately 12,000 daltons. The dissociated factor was found to have a molecular weight <500 daltons, and shared many characteristics with ouabain. Similar to ouabain, this factor was found to be a potent inhibitor of both the Na-K-ATPase and potassium-stimulated para-nitrophenyl phosphatase (K-pNPPase) enzyme systems, and to bind to both high- and low-affinity binding sites on Na-K-ATPase, but unlike ouabain did not cross-react with digoxin antibody. The factor was further separated by HPLC and electrochemical detection into two active compounds (p-NKAI-1 and p-NKAI-2). P-NKAI-1 was demonstrated on mass spectroscopy to have a molecular weight of 408 daltons. In a vasoconstrictor assay employing rabbit femoral artery segments, this compound was a direct vasoconstrictor and potentiated the vasoconstriction produced by norepinephrine. It behaved similarly to ouabain in counteracting the relaxing effect on rabbit femoral artery of increasing potassium concentrations in the tissue bath.

Simultaneous measurement of marinobufagenin, ouabain, and hypertension-associated protein in various disease states

We have previously demonstrated that a 12 kD hypertension-associated protein (HAP) is elevated in essential hypertension and that this protein has the characteristics of natriuresis, inhibition of Na-K-ATPase, displaces 3H-ouabain from binding sites, and is vasoconstrictive in vitro. In the present study, plasma from 101 patients were examined [25 normals (N)age 50, 7 with acute congestive heart failure (CHF), 24 with chronic renal failure (CRF), on dialysis, 5 with idiopathic hyperaldosteronism (PA) and 27 with essential hypertension, untreated (EHT)]. Plasma was extracted with 32% acetonitrile, then analyzed by DELFIA for marinobufagenin and ouabain. In addition, from 32 patients (6 N <50, 6 N >50, 5 CHF, 5 CRF, 6 EHT, and 4 PA) SDS gradient gels were obtained. The 12 kD bands were extracted, analyzed for Na-K-ATPase inhibition, marinobufagenin and ouabain, and compared to 14 kD and 21 kD bands. Marinobufagenin was found to be elevated in CRF, EHT, PA and CHF. Ouabain was increased only in PA. When the relative optical densities of the 12 kD and 21 kD bands were contrasted, CRF, PA, and EHT were found to be increased and CHF to be decreased in the 12 kD band, with no discernible changes in the 21 kD bands. Following extraction of the bands, Na-K-ATPase inhibitory activity measured 38% in 18 pooled 12 kD bands, with essentially no activity found in the 14 kD or 21 kD bands. Thus only the 12 kD HAP band possessed all of the attributes of natriuretic hormone.

Summary of a symposium on natriuretic and digitalis-like factors

An international symposium on natriuretic and digitalis-like factors was convened for the first time since 1992. Topics discussed included structures and biosynthesis of endogenous digitalis-like factors (EDLF), biologic activities, physiology function and role of EDLF in hypertension, and novel natriuretic factors. Progress was reported in determining the exact structure of an isomer of ouabain isolated from bovine hypothalamus. Evidence was presented supporting the existence of a second mammalian EDLF that resembles steroids found in toads (bufodienolides). Support for endogenous synthesis of mammalian EDLF was also presented. Mammalian EDLF were reported to have effects which are different from those possessed by digitalis like steroids derived from plants. New evidence was presented implicating EDLF in various forms of hypertension in humans and animal models. Finally, several unique natriuretic factors that do not inhibit Na, K ATPase and that appear to play a role in mammalian volume regulation were discussed.

Lead-induced hypertension. II. Response to sequential infusions of L-arginine, superoxide dismutase, and nitroprusside

Administration of 100 ppm lead acetate daily for 3 months caused hypertension in Sprague-Dawley rats, with reversal by treatment with 2,3-dimercaptosuccinic acid (DMSA) (0.5% for 2 weeks). Animals from each group were infused sequentially in 30-min intervals with saline (S), L-arginine (Arg), Arg+ superoxide dismutase (SOD), S, and sodium nitroprusside (SNP). Baseline mean blood pressure (MBP) was elevated in lead-treated animals (Pb) compared to that in controls(C), returning toward normal after DMSA (105 +/- 2 mmHg, C, vs 149 +/- 2, Pb, and 124 +/- 1, DMSA, P < 0.001). Infusion of Arg caused a fall in MBP in all animals, normalizing the MBP in Pb-treated animals. SNP caused a greater fall in MBP in all groups of animals, normalizing the MBP in Pb. Measurement of urinary nitrite + nitrate (NOx) by chemiluminescence revealed at baseline a reduced level in Pb, restored to normal by DMSA (6.6 +/- 1.5 nmol/min/100 g BW, C, vs 3.3 +/- 1.7, Pb, P < 0.05, vs 5.8 +/- 2.6, DMSA, P = NS). Infusion of arginine increased urinary NOx in all groups, but to a lesser degree in Pb and DMSA. Assay of plasma malondialdehyde (MDA) by HPLC, as a measure of reactive oxygen species (ROS), was elevated at baseline in Pb, reduced by DMSA (3.6 +/- 0.4 mumol/L, Pb, vs 1.9 +/- 0.2, C, and 1.9 +/- 0.3, DMSA, P < 0.01). In the Pb group, SOD resulted in a significant fall in MDA (2.0 +/- 0.3 mumol/L, SOD, vs 3.1 +/- 0.1, Arg, P < 0.01), but no further fall in MBP or increase in urinary NOx. Thus, hypertension in lead-exposed animals is related to both diminished NO and increased ROS. The elevation in MBP can be ameliorated by additional NO through infusion of substrate arginine or by treatment with the ROS scavenger, DMSA. Lead-exposed animals show enhanced MBP sensitivity to the NO donors, Arg and SNP, but no further response to SOD, despite a reduction in MDA to normal. We speculate that lead-induced hypertension may be caused by one species of ROS which enhances vascular reactivity, and that provision of additional NO acts to scavenge the ROS and/or acts directly as a vasodilator.

Lead-induced hypertension: interplay of nitric oxide and reactive oxygen species

An elevation of mean blood pressure was found in rats treated with low lead (0.01% lead acetate) for 3 months, as contrasted to paired Sprague-Dawley control rats. In these rats, measurement of plasma and urine endothelins-1 and -3 revealed that plasma concentration and urinary excretion of endothelin-3 increased significantly after 3 months (plasma: lead group, 31.8+/-2.2, versus controls, 23.0+1.7 pg/mL, P<.001; urinary excretion: lead group, 46.6+11.7, versus controls, 35.6+6.7 pg/24 h, P<.05), whereas endothelin-1 was unaffected. Plasma and urinary nitric oxide (NO) and cyclic GMP concentrations were not significantly changed. However, assay of plasma and kidney cortex malondialdehyde by high-pressure liquid chromatography, as a measure of reactive oxygen species, was elevated in lead-treated rats compared with that in control rats (plasma: lead group, 4.74+1.27, versus controls, 2.14+.49 micromol/L, P<.001; kidney cortex: lead group, 28.75+3.46, versus controls, 16.38+2.37 nmol/g wet weight, P<.001). There was increased NO synthase activity in lead-treated rat brain cortex and cerebellum. In lead-treated rat kidney cortex, the endothelial constitutive NO synthase protein mass was unaffected, whereas the inducible NO synthase protein mass was increased. These data suggest a balance between increased NO synthesis and degradation (by reactive oxygen species) in lead-treated rats, which results in normal levels of NO. Thus, the hypertension may be related to an increase in the pressure substances, endothelin-3 and reactive oxygen species, rather than to an absolute decrease in nitric NO.

Silicon-related syndrome in dialysis patients

Two dialysis patients with markedly elevated plasma silicon (Si) levels (3,849 and 2,350 micrograms/l, respectively) and a presumed Si-related syndrome are described in this report. One patient presented with transient hypercalcemia in the face of low PTH, vitamin D and plasma A1 levels. Both patients had painful, nodular skin eruptions and aberrant hair growth, characterized as perforating folliculitis on skin biopsy, compatible with known effects of organosilicon compounds in man and animals. Plasma Si was found to be moderately elevated in 30 dialysis patients studied at random (710 +/- 53 micrograms/l, dialysis, vs. 152 +/- 9 micrograms/l, normal control), but there was no significant difference between the arterial values before and after dialysis, implying that the source of Si was ingested foods and fluids rather than dialysate. In these patients, plasma Si was weakly correlated with serum calcium as well as with serum calcium corrected for serum albumen, indicating that Si, like aluminum, may affect calcium metabolism.

Altered nitric oxide metabolism and increased oxygen free radical activity in lead-induced hypertension: effect of lazaroid therapy

Chronic exposure to low levels of lead results in sustained hypertension (HTN) in humans and experimental animals. The mechanism of lead-induced HTN remains unclear. We investigated the possible role of reactive oxygen species (ROS) and their impact on nitric oxide (NO) metabolism in lead-induced HTN. Male Sprague-Dawley rats were treated with lead (100 ppm in drinking water) for twelve weeks. They were then treated with either the potent antioxidant, lazaroid (des-methyl-tirilazad, 5 mg/kg i.p., twice daily) (Pb-Lz group) or placebo (Pb group) for two weeks and monitored for an additional two weeks. A group of normal animals served as controls (N = 6 in each group). Lead administration resulted in marked HTN together with a significant rise in plasma concentration of lipid peroxidation product, malondialdehyde (MDA, reflecting increased ROS generation) and a twofold reduction in urinary excretion of NO metabolites, that is, total nitrates and nitrites (NOx). Lazaroid therapy led to prompt normalization of blood pressure, plasma MDA and urinary NOx. In contrast, blood pressure and plasma MDA remained elevated, and recovery of urinary NOx excretion was slow with placebo therapy. No significant difference was found in creatinine clearance between the study groups during the observation period. Thus, chronic lead exposure resulted in marked HTN coupled with increased ROS production and decreased urinary NOx excretion. Administration of the potent antioxidant, lazaroid, abrogated HTN and reversed the abnormalities of plasma MDA and urinary NOx excretion, thus supporting the role of ROS in lead-induced HTN in this model.

Lead-induced hypertension is not associated with altered vascular reactivity in vitro

In confirmation of a previous study (Am J Hypertens 1993;6:723), mean arterial blood pressure (MBP), as determined by tail cuff plethysmography, was found to be significantly elevated in Sprague-Dawley rats after 3 months of feeding 0.48 mmol/L (100 ppm) lead acetate/day (144 +/- 3.3 [SEM], in lead-treated [L] v 107 +/- 3.3 mm Hg in controls [C], P < .001). Thoracic aorta was excised from L and C animals (n = 6). Segments were suspended in tissue baths with Krebs' bicarbonate solution, then tested sequentially for vasoreactivity to 68 mmol/L K+, followed by graded concentrations of phenylephrine (PE), 0.01 to 0.3 micromol/L, acetylcholine (Ach), 0.001 to 3 micromol/L, nitroprusside (SNP), 0.0001 to 0.1 micromol/L, norepinephrine (NE), 0.001 to 300 micromol/L. There were no differences between L and C animals with respect to either vasoconstrictors (PE and NE) or vasodilators (Ach and SNP). The tissue levels of cGMP measured with and without phosphodiesterase inhibition, and in the absence and presence of either Ach or SNP, were comparable in the two groups. We conclude that the intrinsic vascular responsiveness is unchanged in lead-treated animals. The elevation of MBP is due to the presence of circulating factor(s) and hemodynamic changes.

Osteopenia induced by long-term, low- and high-level exposure of the adult rat to lead

The skeleton, the major site for Pb accumulation, is responsible for the largest fraction of the total body burden, but long-term effects of low-level exposure in adults remain unclear. In this study rats were exposed to low (0.01%; 100 ppm, LoPb) or high (0.5%, 5,000 ppm, HiPb) Pb, low calcium, feeding regimes for 1-12 months. Both LoPb and HiPb animals showed significant 12-month blood Pb levels [LoPb 21 +/- 3 micrograms/dl; HiPb 59 +/- 18; controls 3 +/- 1 (mean +/- SEM), p = 0.001]. Dual energy X-ray densitometry of the femur detected a significant decrease in bone density in HiPb animals by 3 months which remained significantly lowered through 12 months [3 months: HiPb: 0.498 +/- 0.011 (6) vs. control: 0.546 +/- 0.012 (6), p < 0.003]. By 12 months' density was also significantly lowered in LoPb animals (p = 0.001). Mineral analyses of ashed femurs showed a significant lead content after 1, 3, 9 and 12 months' exposure [1 month: LoPb, 0.020 +/- 0.002 (4) (% ash weight) vs control 0.008 +/- 0.0004 (4); HiPb 0.016 +/- 0.001 (8); control 0.007 +/- 0.0004 (6) (p < or = 0.002)]. Ca levels (% ash weight) were significantly lowered at 9 months in HiPb and 12 months in both groups (p < or = 0.04). Quantitative histomorphometry documented significantly elevated osteoid and resorptive trabecular surface features in both Pb groups. The LoPb design produced no overt renal functional abnormalities and resulted in blood Pb values comparable to those in man with modest environmental Pb exposure. The HiPb design resulted in development of lead nephropathy (more severe from months 6-12) and produced blood lead levels comparable to those seen in past industrial exposure. Findings show that Pb is incorporated into bone mineral after only 1 month's exposure to LoPb with significant osteopenia after 12 months' exposure; HiPb caused osteopenia by 3 months. No normal compensatory mechanism was elicited to maintain bone mass. Results stress renewed concern about the effects of cumulative, low-level lead exposure in our elderly population.

Effect of 2,3-dimercaptosuccinic acid on nephrosclerosis in the Dahl rat. I. Role of reactive oxygen species

2,3-Dimercaptosuccinic acid (DMSA), a sulfhydryl-containing chelator, has previously been shown to reduce mean blood pressure in lead-treated rats. In the present study we have demonstrated that DMSA (0.5% for 5 days every 2 weeks) also reduces mean blood pressure in the Dahl salt-sensitive (SS) rat. Six-week-old Dahl SS and salt resistant (SR) rats were placed on a 0.3% NaCl diet for two weeks, followed by an 8% NaCl diet for four weeks. Eight SS and 8 SR rats remained untreated while 8 SS and 8 SR rats were treated with DMSA. DMSA treatment ameliorated the mean blood pressure rise in the Dahl SS rats (141 +/- 5 vs. 120 +/- 4 mm Hg at 6 weeks, P < 0.001). Nephrosclerosis was severe in untreated SS rats but absent in treated SS rats as well as in both treated and untreated SR rats. Reactive oxygen species formation, as assessed by kidney cortex content of malondialdehyde (MDA) and immunohistochemical demonstration of nitrotyrosine (a byproduct of peroxynitrite) in interlobular arteries, was increased in Dahl SS rats, but abolished by DMSA (MDA 9.65 +/- 0.33 nmol/g wet wt, untreated SS, vs. 6.46 +/- 0.51, treated SS, P < 0.001). The anti-nephrosclerotic action of DMSA was clearly disproportionate to the reduction in blood pressure. We conclude that the effect of DMSA was related instead to the reactive oxygen species scavenging properties of the thiol groups.

Relationship of Na-K-ATPase inhibitors to blood-pressure regulation in continuous ambulatory peritoneal dialysis and hemodialysis

Inhibitors of sodium-potassium-activated adenosine triphosphatase (Na-K-ATPase) have been implicated in the pathogenesis of hypertension. In the study presented here, an attempt was made to determine whether differences in the plasma levels and the removal rates of high-molecular weight (HMW) and low-molecular weight (LMW) forms of Na-K-ATPase inhibitors might relate to blood-pressure control in hemodialysis (N = six ultrafiltered and N = six non-ultrafiltered) and CAPD (N = six long-term and N = five short-term) patients. The latter group was studied before the initiation of continuous ambulatory peritoneal dialysis (CAPD) and 2 wk after starting the treatment. The mean blood pressure was significantly reduced after dialysis in the nonultrafiltered hemodialysis group and in both CAPD groups. Plasma levels of both HMW and LMW inhibitors were found to be elevated before dialysis in all patients and were modified only slightly after dialysis. Irrespective of whether ultrafiltration was utilized in hemodialysis patients and despite significant losses of both HMW and LMW inhibitors into CAPD effluent. Because CAPD effluent was found to contain vasopressors that were not exclusively Na-K-ATPase inhibitors, losses of these other vasopressors may contribute to improved blood-pressure control in CAPD in contrast to hemodialysis.

Effect of chelation treatment with dimercaptosuccinic acid (DMSA) on lead-related blood pressure changes

An elevation in mean blood pressure was found in rats treated with low lead (0.01%) for 6 months and then only water for an additional 6 months (discontinuous low lead). No change in blood pressure was found in rats similarly treated with high lead (0.5%) (discontinuous high lead). Administration of DMSA (0.5% in drinking water), for 5 days every 2 months following cessation of lead administration, resulted in a significant lowering of blood pressure in both groups of animals. In the low-lead but not the high-lead group, this was associated with an increase in plasma cyclic GMP (acting as a second messenger for endothelium-derived relaxing factor, EDRF) and a decrease in the plasma concentration of a 12-kDa hypertension-associated protein. Plasma endothelin-3 (ET-3) levels were decreased in discontinuous high-lead rats, increased in discontinuous low-lead rats, but were unaltered by DMSA treatment. We infer that the elevated blood pressure in the discontinuous low-lead rats is related to an increase in the putative vasoconstrictors, ET-3 and the hypertension-associated protein, without a change in the vasodilator, EDRF. With DMSA treatment, plasma cyclic GMP in low-lead rats increased above normal, and the hypertension-associated protein decreased, resulting in lowered blood pressure. DMSA was shown to act as an antioxidant in vitro. Thus the DMSA effect on plasma cGMP (EDRF) may occur via a scavenging effect on EDRF-inactivating reactive oxygen species.

Experimental model of lead nephropathy. IV. Correlation between renal functional changes and hematological indices of lead toxicity

Adverse effects on hematopoiesis and renal function have been reported in both animals and humans exposed to high doses of lead for a protracted period of time, but little is known about the interrelationship between these two target organ systems. The present study examines rats exposed via drinking water to high dose (5000 mg/L) or low dose (100 mg/L) lead, either continuously or discontinuously, for periods ranging from 1 to 12 months. In addition to blood lead, indices of hematological abnormalities included hematocrit, zinc protoporphyrin (ZPP) and red blood cell (RBC) membrane sodium-potassium-activated adenosine triphosphatase (Na-K-ATPase). Renal function abnormalities were assessed by measurements of glomerular filtration rate (GFR) by the single injection 125-I-iothalamate technique and urinary excretion of the proximal renal tubular enzyme, ligandin. Blood lead and GFR correlated positively during the first 6 months of lead administration, reflecting a stimulatory effect of lead on renal hypertrophy and GFR during this time period. When this distorting effect was factored out, there were few residual correlations between renal and hematological abnormalities. The only significant relationship between GFR and hematological parameters of lead toxicity was a negative correlation between GFR and RBC membrane Na-K-ATPase in animals treated with high dose lead for 6 months and observed at the end of 12 months (discontinuous group).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a low molecular weight Na-K-ATPase inhibitor of urinary origin

It has been demonstrated that expansion of extracellular fluid volume induces the release of a low-molecular-weight natriuretic and sodium-potassium-activated adenosine triphosphatase inhibiting hormone (NKAI). In this study, we used a highly purified hormone extracted from pooled hypertensive urines (u-NKAI). Like ouabain, this compound was found to be a potent inhibitor of the sodium-potassium-activated adenosine-triphosphatase and potassium-stimulated paranitrophenyl phosphatase enzyme systems as well as a vasoconstrictor in vitro. In contrast to ouabain, which is a competitive inhibitor of both enzyme systems with respect to potassium, u-NKAI is noncompetitive. Furthermore, u-NKAI differs from ouabain by its lack of cross-reactivity with digoxin antibodies. In addition, whereas ouabain binds to both high-affinity and low-affinity binding sites on the sodium-potassium-activated adenosine-triphosphatase enzyme in the absence of potassium, u-NKAI binds only to the low-affinity binding sites. This study demonstrates that the highly purified u-NKAI, although ouabain-like in certain respects, is not an "endogenous ouabain."

Lead-induced hypertension: possible role of endothelial factors

The results of this study confirm that low lead (0.01%) but not high lead (0.5%) administration results in increased blood pressure in rats treated for up to 12 months. This effect appeared to be related to an imbalance of endothelially-derived vasoconstrictor and vasodilator compounds in low lead-treated animals but not in high lead-treated animals. In low lead-treated rats, measurement of plasma endothelins 1 and 3 (ET-1 and ET-3) revealed that ET-3 concentration increased significantly after both 3 months (Experimental, 92.1 +/- 9.7 v Control, 46.7 +/- 12.0 pmol/mL; P < .001) and 12 months (Experimental, 105.0 +/- 9.3 v Control, 94.1 +/- 5.0 pmol/mL; P < .01) while ET-1 was unaffected. Plasma and urinary cGMP concentrations (as a reflection of endothelium-derived relaxing factor (EDRF)) decreased significantly at 3 months (plasma, Experimental, 1.8 +/- 0.9 v Control, 4.2 +/- 1.6 pmol/mL; P < .001) and 12 months (plasma, Experimental, 2.2 +/- 0.7 v Control, 4.2 +/- 0.9 pmol/mL; P < .001). Thus, the path to development of hypertension in low lead rats may be through an increase in the concentration of the vasoconstrictor hormone, ET-3, and a decrease in the vasodilator hormone, EDRF. High levels of lead exposure did not result in hypertension, perhaps because plasma concentrations of ET-1, ET-3 and cGMP were unaltered at 3 months, while ET-1, ET-3 and cGMP concentrations were coordinately and significantly decreased at 12 months.

Predominance of high molecular weight plasma Na(+)-K(+)-ATPase inhibitor in essential hypertension

Circulating inhibitors of the transport enzyme, sodium-potassium-activated adenosine triphosphatase (Na(+)-K(+)-ATPase), have been shown to be of possible pathogenetic importance in the mechanism of essential hypertension. Although previous studies have demonstrated the presence of both high molecular weight (HMW) and low molecular weight (LMW) natriuretic plasma Na(+)-K(+)-ATPase inhibitors, no previous attempts have been made to ascertain whether HMW or LMW forms predominate in hypertension. In this study, plasma samples obtained from 26 patients with essential hypertension, 12 normotensive controls, and six normotensives with a family history of hypertension, were separated into HMW and LMW moieties by passage through a 1 kDa Amicon membrane. The LMW moiety was separated on C18 Sep-Pak cartridges, applying a 10% step-wise acetonitrile trifluoroacetic acid gradient. The HMW moiety was further separated on Sephadex G-75. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that the fraction with inhibitory activity contained a distinct 12 kDa protein band, with staining intensity depending on the presence or absence of hypertension. Na(+)-K(+)-ATPase inhibitory activity was found in several LMW fractions, but differences between hypertensives and normotensives were observed in only one fraction (0.29 +/- 0.12 SD v 0.11 +/- .12 mumol/L ouabain equivalents, P < .01). Na(+)-K(+)-ATPase inhibitory activity in the HMW fraction was 38 x the inhibitory activity in the LMW fraction and was significantly increased in hypertensives as compared to normotensive controls (10.9 +/- 8.9 v 1.3 +/- 0.8 mumol/L ouabain equivalents, P < .01). Inhibitory activity in both HMW and LMW fractions correlated positively with mean blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental model of lead nephropathy. III. Continuous low-level lead administration

We sought to determine whether continuous low-level lead exposure (100 ppm lead acetate in drinking water) for periods of 1, 3, 6, 9, or 12 mo would produce adverse effects on kidney function or morphology in rats. Maximum blood lead levels in experimental animals were reached at 3 mo and averaged 29.4 +/- 4.1 micrograms/dl. Glomerular filtration rate, determined by single-injection 125I-iothalamate clearance, was found to be significantly increased above pair-fed controls at 1 and 3 mo, but it was normal at other time periods. Levels of urinary N-acetyl-beta-D-glucosaminidase exceeded levels found in controls at all time periods, except at 12 mo, when the normal increase with aging obscured differences between experimental animals and controls. In contrast, urinary ligandin (glutathione S transferase), a more specific marker of metal-associated proximal tubular injury, was normal at all time periods. Proximal tubular nuclear inclusion bodies were sparse and were observed only at 1 and 3 mo. There were no other pathological alterations in the kidneys, except at 12 mo, at which time mild tubular atrophy and interstitial fibrosis were seen. Therefore, low-level lead exposure in rats produced no significant changes in renal function and produced only mild alterations in renal morphology after 12 mo. The absence of changes in urinary ligandin accorded with the relative absence of morphological changes, whereas the observed increases in urinary N-acetyl-beta-D-glucosaminidase suggest that this enzyme may be an overly sensitive indicator of tubular injury.

Effect of continuous ambulatory peritoneal dialysis on blood pressure control

To assess the efficacy of blood pressure control in continuous ambulatory peritoneal dialysis (CAPD), blood pressure was examined sequentially in 63 CAPD patients transferred from hemodialysis (HD), and in 97 patients started de novo on CAPD (NEW), over periods ranging from 3 to 63 months. Blood pressure changes were related to changes in body weight, hematocrit, and treatment with recombinant human erythropoietin (rHu-EPO), as well as to changes in antihypertensive drug requirements. Both groups of patients showed an immediate improvement in blood pressure control at 1 month, as manifested by an absolute decrease in blood pressure in HD patients (-4.3% +/- 2.1% [SEM], P < 0.05) and by a decrease in antihypertensive drug requirements in NEW patients (from 78% to 43.3%). This early improvement in blood pressure appeared to be volume-related, as reflected by changes in body weight. Both groups showed an additional decrement in blood pressure at approximately 6 months (-7.8% +/- 2.6% [SEM], P < 0.05, HD group; -3.4% +/- 2.4% [SEM], P < 0.05, NEW group). Treatment of anemia with rHu-EPO in 22 of the CAPD patients had no effect on blood pressure. CAPD thus appears to be more effective than HD in controlling blood pressure.

Comparison of low-molecular-weight plasma and urine Na-K-ATPase inhibitors/hypertensive factors

Two highly purified low-molecular-weight (< 500 Da) Na-K-ATPase inhibitors, one originating from human plasma and the second from human urine, which both eluted in the identical locus from a C18 reversed-phase high-pressure liquid chromatography (HPLC) column, were compared with respect to (a) K effect on Na-K-ATPase inhibition; (b) displacement of [3H]ouabain from binding sites on purified hog brain Na-K-ATPase; (c) cross-reactivity with digoxin antibodies; and (d) vasoconstrictor effects in isolated rabbit femoral arteries. Inhibition of Na-K-ATPase by the plasma factor correlated inversely with K concentration, whereas inhibition by the urine factor correlated directly with K concentration. In the absence of K, the plasma factor displaced [3H]ouabain from both high- and low-affinity binding sites, whereas the urine factor displaced [3H]ouabain only from the low-affinity binding site. Neither factor possessed digoxin-like immunoreactivity. Both factors acted as direct vasoconstrictors, and potentiated the vasoconstrictor action of norepinephrine. The degree of vasoconstriction caused by the plasma factor diminished progressively with added K, indicating that the vasoconstrictor effect of this factor was mediated by the Na-K-ATPase pump. Thus, although both the plasma and urine Na-K-ATPase inhibitors are vasoconstrictors, their mechanisms of action are different.

Experimental model of lead nephropathy. I. Continuous high-dose lead administration

This study followed the progression of lead nephropathy in male Sprague-Dawley rats (E) administered lead acetate (0.5%) continuously in drinking water for periods ranging from 1 to 12 months. Control animals (C) were pair-fed. Observations included renal pathology by light and electron microscopy, wet and dry kidney weights, and glomerular filtration rate (GFR) to assess renal function. Urinary excretion of lead, the enzymes N-acetyl-beta-D-glucosaminidase (NAG) and glutathione-S-transferase (GST), and brush border antigens (BB50, CG9, and HF5) were utilized to explore possible markers of kidney injury. GFR was increased significantly after three months of lead exposure, but was decreased significantly after 12 months. Kidney wet weights were significantly greater in E than C from three months on. Kidney dry weight/wet weight ratio was constant up to three months, but decreased in E at 12 months. Glomerular diameters were normal at all time periods; the nephromegaly was related primarily to hypertrophy of proximal tubules. Lead inclusion bodies were found in nuclei of proximal convoluted tubules and pars recta at all times. Tubular atrophy and interstitial fibrosis first appeared at six months, and increased in severity thereafter. Brush borders of proximal tubules were disrupted at one and three months, but recovered thereafter. Focal and segmental glomerulosclerosis was observed in 2 of 10 rats at 12 months. Arteries and arterioles remained normal at all time periods. Urinary NAG was elevated in E above C after three months of lead exposure. However, urinary NAG in C also increased with age, obscuring changes in the 12 month E rats. GST was elevated after three months of lead administration in E, not without an attendant age-related increase in C rats. In three-month E rats, urinary brush border antigens were increased above C, but were decreased at six and 12 months, correlating with the morphologic changes in brush border. We conclude that a high dose of lead in rats may initially stimulate both renal cortical hypertrophy and an increase in GFR. Later, the adverse effects of lead on the tubulointerstitium predominate, and GFR falls. The urinary marker, NAG, was abnormal in the early stages of the disease, but age-related changes obscured its utility at later stages; urinary GST appeared to be a more consistent marker of injury.

Effects of lead and a low-molecular-weight endogenous plasma inhibitor on the kinetics of sodium-potassium-activated adenosine triphosphatase and potassium-activated p-nitrophenylphosphatase

1. Lead, ouabain and an endogenous plasma inhibitor were all found to be potent inhibitors of purified hog cerebral cortex sodium-potassium-activated adenosine triphosphatase and potassium-stimulated p-nitrophenyl-phosphatase. 2. The kinetic characteristics of inhibition of both enzymes by lead and the endogenous plasma inhibitor differed in several respects. For sodium-potassium-activated adenosine triphosphatase, lead and the endogenous plasma inhibitor were non-competitive inhibitors with respect to potassium; lead was competitive with respect to sodium, whereas the endogenous plasma inhibitor had no effect; lead was competitive with respect to magnesium adenosine triphosphate, whereas the endogenous plasma inhibitor was uncompetitive. For potassium-activated p-nitrophenylphosphatase, both lead and the endogenous plasma inhibitor were competitive with respect to potassium; lead showed a mixed type of inhibition with respect to p-nitrophenylphosphate, whereas the endogenous plasma inhibitor was non-competitive. 3. Lead and the endogenous plasma inhibitor exhibited synergistic inhibitory activity on sodium-potassium-activated adenosine triphosphatase. 4. These results suggest that lead could play a contributory role in the pathogenesis of essential hypertension via an additive inhibition of vascular smooth muscle sodium-potassium-activated adenosine triphosphatase.

Effects of a human-derived sodium transport inhibitor on in vitro vascular reactivity

Concentrations of sodium-transport inhibitors (STI) which block the sodium-potassium-ATPase pump are increased in the plasma and urine of volume-expanded and low-renin hypertensive humans and animals. To evaluate the physiologic relevance of STI to blood-pressure-raising mechanisms, we have examined the in vitro properties of STI extracted from the urine of human subjects. STI produced a significant (by ANOVA: P less than .01) dose-contraction response in the isolated rabbit femoral artery. Moreover, small noncontractile doses of STI in this in vitro preparation produced a fivefold leftward shift in the contraction dose-response curve of norepinephrine (P less than .01) and a threefold shift for angiotensin II (P less than .01); at lower, physiologic, concentrations of these vasoconstrictor hormones the amplifications in contraction caused by STI ranged from 100% to 500%. In studies in calcium-free tissue bath solutions, the direct contractile action of STI was abolished; however, its amplification of responses to norepinephrine remained, suggesting that this latter effect of STI is not entirely dependent upon calcium influx into vascular smooth muscle cells. The glycoside ouabain produced effects identical to those of STI in arteries, but its actions on a rabbit atrium preparation were different: ouabain stimulated powerful inotropic effects, whereas human STI failed to cause myocardial contractions even though the amounts of STI administered had the same sodium-transport inhibitory capacity as the ouabain. Thus, the actions of human STI are primarily in the peripheral circulation, where they directly produce arterial contractions and also enhance contractile responses to other pressor hormones, suggesting that they may have a role in regulating systemic blood pressure.

Renal lesions and clinical findings in thalassemia major and other chronic anemias with hemosiderosis

Renal lesions found in 21 autopsied patients with hemosiderosis, 18 with beta-thalassemia, two with Blackfan-Diamond anemia, and one with aplastic anemia included: cellular glomeruli with increased mesangial matrix; hemosiderin deposit in visceral and parietal glomerular epithelial cells; greater hemosiderin deposit in terminal straight portions of proximal convoluted tubules and distal convoluted tubules than in connecting segments, or collecting tubules, connective tissue ferrugination; lipofuscin in tubular epithelium and vascular smooth muscle; infrequently, intimal or medial arterial thickening, and, in one patient with thalassemia, an infarct resulting from arterial thrombus. The progression of these lesions over the course of disease, and possible effects on the various lesions of high transfusion regimen, oral pancreatin, vitamin E supplementation, or treatment with intramuscular, subcutaneous, or intravenous desferrioxamine were evaluated. The results of urine and renal function studies of 4 of the autopsied patients (3 thalassemia, 1 Blackfan-Diamond anemia), and 14 patients with thalassemia and 4 with Blackfan-Diamond anemia who were not autopsied, are presented. Rarely significant until preterminal stages, the renal functional changes reflect distal more than proximal tubule dysfunction.

Aluminum-binding protein in dialysis dementia. II. Characterization in plasma by ultrafiltration

Ultrafiltration experiments, using Amicon membranes with molecular weight exclusions of 1,000, 10,000 and 30,000 daltons, have revealed that Desferal, both in vitro and in vivo, markedly increases aluminum ultrafilterability in plasma from patients with dialysis dementia. Ultrafilterability was greater with the 10,000-dalton membrane (60%) as compared with the 1,000-dalton membrane (40%); the difference could be related to the presence of an 8,000-dalton aluminum-binding protein in the 10,000-dalton filtrate. These observations are pertinent to in vivo dialysis studies which have demonstrated enhanced aluminum clearance with high-permeability polyacrylonitrile dialysis membranes.

Aluminum-binding protein in dialysis dementia. I. Characterization in plasma by gel chromatography and electrophoresis

A low molecular weight (approx. 8,000 daltons) protein has been found to be the major aluminum-binding protein in plasma of patients with dialysis dementia. Following treatment with desferrioxamine, the concentration of the low molecular weight protein and its aluminum content rise in parallel. The results suggest that aluminum exposure in dialysis dementia may result in the de novo synthesis of an aluminum-binding protein and that desferrioxamine may release aluminum in conjunction with its binding protein from tissue stores.

Pattern of Na-K-ATPase inhibitors in plasma and urine of hypertensive patients: a preliminary report

The pattern of endogenous Na-K-ATPase inhibitors in plasma and urine from patients with essential hypertension and normal controls was established by sequential Amicon ultrafiltration through membranes with molecular weight cut-offs of 50 K daltons, 30 K daltons and 1 K daltons, followed by C18 Sep-Pak cartridge separation of the 1 K filtrate. Significantly increased Na-K-ATPase inhibitory activity in the hypertensive population was found in a high molecular weight (30-50 K daltons) urine fraction, one low molecular weight (less than 1 K daltons) urine fraction and two low molecular weight plasma fractions. Preliminary evidence is presented to suggest that large molecular weight plasma fractions may contain a "masked" Na-K-ATPase inhibitor, in either carrier or precursor form.

In vitro inhibition of Na-K-ATPase by trace metals: relation to renal and cardiovascular damage

The potential role of trace metals in the pathogenesis of various disease states, especially of renal and cardiovascular disease, has been recognized increasingly. Moreover, altered membrane transport was recently incriminated to play a role in renal tubular syndromes, such as the Fanconi syndrome, as well as in the pathogenesis of volume dependent hypertension. We therefore investigated the possible in vitro effects of various trace metals on Na-K-ATPase, the biochemical correlate of active cellular transmembrane sodium and sodium-dependent transport. To more closely mimic the in vivo situation, we deliberately chose as enzyme source renal tissue homogenate, which may contain protective agents. Under these experimental conditions, the metals studied inhibited the enzyme quantitatively in the following order: Hg greater than Pb greater than Cd greater than Ur greater than Cu greater than Zn greater than Mn greater than Ba greater than Ni greater than Sr. Enzyme kinetic studies showed that Hg, Pb, and Cd competitively, and Cu noncompetitively, inhibited the enzyme. In general, Mg-ATPase was significantly less sensitive to the trace metals. Accumulation of these metals may present serious health hazards by producing a general defect in cell membrane transport. From the other metals studied, i.e., Mn, Ba, Ni and Sr, some may have toxic effects via other mechanisms, whereas some may exert a protective role against toxicity of other agents including metal ions.

Observations on the "cascade" of Na-K-ATPase inhibitory and digoxin-like immunoreactive material in human urine: possible relevance to essential hypertension

Previous investigations have demonstrated an increased amount of a sodium pump inhibitor (N.H.) in plasma from humans with essential hypertension and from animals with various forms of experimental hypertension. The present study has employed Sephadex column and C18 reverse phase separation of urines from patients with essential hypertension and normal controls to distinguish "high", "intermediate" and "low" molecular weight forms of N.H., measured through properties of Na-K-ATPase inhibition and digoxin-like immunoreactivity. The major difference between hypertensive and normotensive urines was a highly significant increase in the "intermediate" molecular weight form of N.H., as measured by Na-K-ATPase inhibition. In contrast, digoxin-like immunoreactivity was significantly decreased in urine from hypertensive patients. The results are compatible with an hypothesis that the defect in some forms of essential hypertension may be partial inhibition of enzymatic conversion of intermediate to final form of N.H., with the increased sodium pump inhibition primarily related to the precursor.

Clinical trial of chromium and yeast supplements on carbohydrate and lipid metabolism in diabetic men

Chromium (Cr) deficiency in experimental animals and in humans sustained by prolonged total parenteral nutrition has been shown to cause diabetes mellitus. Prior trials in humans indicated that Cr supplements, in either inorganic or organic form, may improve carbohydrate utilization. We report here a clinical double-blind, random cross-over trial of inorganic chromium trichloride, a brewer's yeast that contained Cr as glucose-tolerance-factor (GTF), a brewer's yeast extract without GTF, and a placebo. Forty-three outpatient diabetic men received three of these supplements for 4 months each. Subgroups included 21 ketosis-prone, 7 ketosis-resistant non-obese, and 15 ketosis-resistant obese men. Cr levels were followed pre- and post-treatment in hair, red blood cells, plasma, and urine. Response of carbohydrate metabolism to treatment was assessed in terms of change in insulin requirements, fasting plasma glucose, plasma cholesterol, and triglycerides, as well as the change in plasma glucose, glucagon, and insulin or C-peptide levels in response to a standard meal. In some men, these parameters were also measured after iv tolbutamide. Both the inorganic and organic oral Cr supplements increased measurable body pools of Cr in hair and red blood cells by about 25%. However, fasting plasma glucose and lipids and the glucose response to either the standard meal or to tolbutamide were not significantly altered by any of the treatments.

Effects of chromium and yeast supplements on carbohydrate and lipid metabolism in diabetic men

Diabetes mellitus has been shown to develop as a consequence of chromium (Cr) deficiency in experimental animals and in humans sustained by prolonged total parenteral nutrition. Prior limited trials in humans had indicated that Cr supplements, in either inorganic or organic form, may improve carbohydrate utilization. We report here a clinical double-blind, random crossover trial of inorganic Cr trichloride, a brewer's yeast that contained Cr as glucose tolerance factor (GTF), a brewer's yeast extract without GTF, and a placebo. Forty-three outpatient diabetic men received three of these supplements for 4 mo each. Subgroups included 21 ketosis-prone men; 7 ketosis-resistant, nonobese men; and 15 ketosis-resistant obese men. Chromium levels were followed pre- and posttreatment in hair, red blood cells, plasma, and urine. Response of carbohydrate metabolism to treatment was assessed in terms of change in insulin requirements, fasting plasma glucose, plasma cholesterol, and triglycerides, as well as change in plasma glucose, glucagon, and insulin or C-peptide levels in response to a standard meal. In some men, these parameters were also measured after i.v. tolbutamide. Both the inorganic and organic oral Cr supplements increased measurable body pools of Cr in hair and red blood cells by about 25%. However, fasting plasma glucose and lipids and the glucose response to either the standard meal or to tolbutamide were not significantly altered by any of the treatments. Despite this lack of effect on carbohydrate levels, the ketosis-resistant subgroups demonstrated a significant increase in postprandial insulin after treatment with the brewer's yeast that contained GTF.

Pathophysiology of human proximal tubular transport defects

The generalized proximal tubular transport abnormalities comprising the Fanconi syndrome (glycosuria, generalized aminoaciduria, the proximal form of renal tubular acidosis, and increased renal clearance of phosphate, urate, calcium, magnesium, and potassium) may be ascribed to interference with "sodiumlinked" active transport. Evidence is presented that the majority of conditions known to cause Fanconi syndrome in man or experimental animals are associated with inhibitors of the renal Na-K-ATPase-ATP transport system.

Subclinical effects of chronic increased lead absorption--a prospective study. Part IV. Evaluation of heme synthesis effects

The effects of lead exposure on heme synthesis in workers with subclinical responses and in controls were evaluated. delta-Aminolevulinic acid dehydratase (ALA-d) correlated significantly with blood lead levels in the control group but not with those in the exposed group. Free erythrocyte protoporphyrin correlated significantly with blood lead levels in the exposed group but not with those in the controls and was found to be a good indicator of blood lead history among exposed persons. Hemoglobin values determined at initial employment were not statistically different from those determined during the baseline test for a group of 12 workers with a maximum blood lead level of 86 micrograms/100 ml during their exposure history. The effect such heme inhibition may have on other body functions is uncertain.

Erythrocyte lead-binding protein after occupational exposure. II. Influence on lead inhibition of membrane Na+,K+-adenosinetriphosphatase

Membrane Na+,K+-adenosinetriphosphatase in erythrocytes from three groups of industrially exposed Pb workers (without toxicity, with toxicity associated with high blood Pb levels, and with toxicity associated with low blood Pb levels) was inversely correlated with Pb in the membrane fraction but not significantly correlated with total erythrocyte Pb. This difference was attributable to the proportion of erythrocyte Pb bound to hemoglobin and a Pb-binding protein of molecular weight 10,000.

Subclinical effects of chronic increased lead absorption--a prospective study. II. Results of baseline neurologic testing

This report summarizes the results of baseline neurologic testing in a group of apparently healthy workers from a secondary lead smelter and a group of controls from nearby aluminum processing plants. The test battery included a standard neurologic examination nerve conduction measurements, quantitative oculomotor function tests and detailed audiologic studies. Lead workers and controls were intermixed so that the examiners were unaware of the status of any individual being tested. Although the lead workers reported significantly more neurologic symptoms than the controls, relatively few differences were found on quantitative neurologic testing. Decreased deep tendon reflexes occured more frequently in the lead workers than in the controls (22% vs. 11%) but the difference was of borderline significance (p=0.06) and other signs of peripheral neuropathy occurred with equal frequency in both groups. The mean motor conduction velocity and sensory latency measurements were not significantly different in the lead workers and in the controls and, of the six oculomotor function measurements, only the mean accuracy of saccadic eye movements was significantly (p less than 0.01) different in the two groups. High frequency hearing loss occurred with equal frequency and severity in both groups, consistent with the level of noise exposure in the lead and control plants.

Circulating inhibitor of sodium-potassium-activated adenosine triphosphatase after expansion of extracellular fluid volume in rats

1. Serum was collected from normal rats and from rats volume-expanded with isotonic sodium chloride solution. 2. The serum was fractionated by gel filtration on Sephadex G-25 and each fraction was tested for inhibitory activity against sodium-potassium-activated adenosine triphosphatase prepared from rat kidney homogenate. 3. A single low-molecular-weight fraction, eluting after the salts and after exogenously added lysine-vasopressin, had significantly greater enzyme inhibitory activity when obtained from serum of volume-expanded animals than from control serum. 4. As this fraction has been shown in previous independent studies to contain a natriuretic factor, it may be concluded that one property of this factor is the ability to inhibit sodium-potassium-activated adenosine triphosphatase.

Pathogenesis of renal calculi in distal renal tubular acidosis. Possible role of parathyroid hormone

Elevated circulating levels of immunoreactive parathyroid hormone (PTH), hypercalciuria and renal calculi were found in 3 patients with distal renal tubular acidosis (RTA). Treatment with alkali resulted in a fall of PTH toward normal and a reduction in urinary calcium, but the frequency of urolithiasis was unchanged. In one patient in whom prolonged follow-up was possible, a subtotal parathyroidectomy was performed. This was followed by virtual cessation of stone formation despite persistence of the acidification defect. This study suggests that RTA may be associated with secondary hyperparathyroidism and that the consequent elevation in PTH may play a contributory role in the pathogenesis of renal calculi.