The effect of chelating agents on lead excretion in rats in relation to age.

The purpose of the present work was to determine the influence of age on the effectiveness of chelating agents in enhancing lead elimination from the body.Using the method of ²⁰³Pb-labeling, three doses of lead in the form of acetate (1.0 μg/kg, 0.5 mg/kg, 5.0 mg/kg) were applied intraperitoneally or intravenously to female albino rats aged 15 days and 18 weeks. Solutions of EDTA and of BAL (0.2 mmole/kg) were administered by a single or repeated intraperitoneal injection immediately after lead had been given. The whole body retention of ²⁰³Pb was measured at various time intervals in a twin crystal assembly.Both chelating agents caused a lower excretion of lead in 15-day-old rats than in adult animals. The poorer efficiency of chelating compounds in immature organisms was found to be independent of the lead dose, route of lead administration, chelating agent:metal molar ratio, and frequency of chelating treatment. The authors introduce the concept of a lower “free lead” level, due to a higher stability and/or inertness of lead linkages with body ligands in the growing organism as an explanation of the results obtained.     

The effect of particle size on absorption of inhaled lead.

Baboons were exposed to dust clouds of Ph3O4 of different size distribution but of the same total gravimetric concentration. Blood samples were taken immediately after each exposure of 4 hours and the total blood lead was determined. The exposure to the lead-bearing dust was stopped after four weeks, but the blood sampling continued for another six weeks. Graphs are presented comparing the patterns of lead absorption obtained with different sized lead particles. The coarser lead particles resulted in a higher blood lead concentration than the finer.     

Long-term effect of increased lead absorption on intelligence of children.

The authors examined the reversibility of cognitive impairment caused by a mild increase in lead absorption among children. The results of our initial study revealed that air and soil outside a lead-recycling plant in Taiwan were seriously contaminated by lead, which was associated with lowered intelligence quotients of 32 children who attended a nearby kindergarten (i.e., kindergarten A). Thirty-five children-who were comparable with respect to age, sex, birth order, sibling number, and parental education level-from another kindergarten (i.e., kindergarten B) located 5 km from the plant were enrolled as the reference group. Following the initial study, kindergarten A school children moved 2 km from the lead-recycling plant. Twenty-eight children in each group were followed successfully 2.5 y later. Blood lead, intelligence quotient, and intelligence quotient-related factors were reassessed. The results showed that the average blood lead level of the exposed pupils dropped 6.9 microg/dl (standard deviation [SD] = 3.9 microg/dl) (p < .001), and the average intelligence quotient increased 11.7 points (SD = 13.2) (p < .01), compared with the results of the initial study. The average blood lead level of the reference group decreased by 1.7 microg/dl (SD = .1.3) (p < .001), whereas the average intelligence quotient increased by 4.2 points (SD = 13.8) (p = .115). There was a significant difference in intelligence quotients between the two groups during the initial study, but the difference subsequently disappeared during the follow up. The authors concluded that intelligence quotient impairment, caused by a mild subclinical elevation of blood lead (i.e., likely no more than 30 microg/dl) for a period of 1-3 y in 3- to 5-y-olds, is at least partially reversible.     

The effect of cellulose and glucomannan on the absorption of lead in rats]

The effect of two different fibers on lead (Pb) absorption was investigated during two 3-day balance-study periods (day 15th to 17th and 30th to 32nd) of a 32-day feeding course in young rats. Young rats were fed for 32 days diets containing Pb (200 mg/kg diet), with or without the addition of 10% cellulose or glucomannan. The following results were obtained: 1) The total fecal Pb content was significantly increased (p less than 0.05) in the Pb + cellulose group than in the Pb alone group during both balance-study periods. However, there was no significant difference between the Pb alone group and the Pb + glucomannan group. 2) Lead retention was significantly lower (p less than 0.05) in the Pb + cellulose group than in the Pb alone group during both balance-study periods. However, there was no significant difference observed between the Pb alone group and the Pb + glucomannan group. 3) Rats fed on the Pb + glucomannan diet had a significantly heavier (p less than 0.05) cecum and large intestine than rats fed on the other two diets. 4) The concentration of Pb in the cecum was significantly lower (p less than 0.05) in the Pb + cellulose group than in the other two groups. These results indicate that cellulose supplementation reduced the retention of Pb, while glucomannan supplementation had no significant effect on the retention of Pb.     

Renal excretion of ascorbic acid: effect of age and sex.

To determine if the lower plasma ascorbic acid concentrations observed in males compared to females, and in the elderly in general, might be due to differences in renal clearances of ascorbic acid, tubular maximum reabsorptions (TmAA) and renal thresholds for ascorbic acid were determined on older (10 male, 10 female, aged 70-86 years) and younger (3 male, 5 female, aged 26-59 years) subjects. The mean TmAA for men was 1.54 +/? 0.29 and for women 1.39 +/? 0.33 mg/minute/100 mL glomerular filtration rate (p > 0.05). The mean renal threshold for men was 1.51 +/? 0.25 and for women 1.26 +/? 0.16 mg/dL (p < 0.02). Neither was affected by age. If differences in TmAA and renal threshold were to explain the lower plasma ascorbic acid concentrations observed in males, both values should have been lower than in females. The ability of women to maintain higher plasma ascorbic acid concentrations than men, and young higher than elderly, cannot be explained by differences in the renal handling of ascorbic acid.     

营养素对铅吸收的影响

20世纪50年代以前,重度铅中毒曾是儿童死亡的原因之一。近年来,西方发达国家采取强有力的措施限制汽油和油漆中铅含量,儿童铅中毒(重度)已属罕见。但低水平的铅暴露尤其是对儿童智力、行为发育的危害仍是一个重要的公卫问题。美国疾病控制和预防中心认为,值得忧虑的血铅水平,成人为     

The effect of past and current dietary Zn intake on Zn absorption and endogenous excretion in the rat

Effects of previous dietary Zn (or body Zn stores) and current dietary Zn intake on absorption and endogenous excretion of Zn were studied by using radioisotope dilution. Rats were fed diets containing 1.5, 12.6 or 50.3 mg Zn/kg for 19 d (dietary period I). Total body Zn in the three groups was 1870 +/- 340, 3953 +/- 698 and 4126 +/- 844 micrograms Zn/rat. Each group was divided into four subgroups fed 3.6, 12.6, 20.5 or 50.3 mg Zn/kg diet for 3 wk (dietary period II). Rats were injected intramuscularly with 65Zn after 7 d of dietary period II. True absorption and endogenous excretion were calculated by isotope dilution. Zinc intake, urinary and fecal excretion, balance and percent Zn absorption were significantly affected only by dietary Zn in dietary period II (P less than 0.01). Endogenous excretion was affected by both past dietary Zn deficiency (body Zn stores) and by dietary Zn in dietary period II (P = 0.0001). Total body Zn at the end of the experiment was significantly affected by both periods of dietary treatment (P less than 0.001), but total body Zn concentration was affected only by the final dietary treatment (P less than 0.05). These results show that Zn absorption is affected by the current diet, but that turnover of Zn (endogenous excretion) is regulated by both current Zn intake and past Zn intake, probably through an effect on body Zn stores.     

Blood lead and the symptoms of lead absorption

ABSTRACT Eighty-one percent of all hourly paid men who had been employed for more than six months in a factory making lead acid batteries and plastics completed a modified Cornell medical index health questionnaire. Blood lead and erythrocyte protoporphyrin (EPP) were also measured. The questions were grouped into symptom categories as follows: all physical, all psychological, “potentially lead induced,” pulmonary, cardiovascular, gastrointestinal, skin, nervous system, genitourinary, and fatigue. For each symptom category the pooled percentages of men whose symptom scores were above the common median of the three blood lead groups 10-, 40-, and 60 and over μg/100 ml (0·48-, 1·93-, and 2·90 and over μmol/l) within age/smoking subgroups were calculated. In every symptom category the percentages in the two lower blood lead groups differed little, but the percentages were consistently higher in men with blood concentration of 60 μg/100 ml (2·90 μmol/l) and over. Differences between a combined 10-59 μg/100 ml (0·48-2·85 μmol/l) blood lead group and the 60 and over μg/100 ml (≥2·90 μmol/l) group were statistically significant at the 0·01 level for “potentially lead induced” symptoms and at the 0·05 level for skin and psychological symptoms. Broadly similar results were obtained with four log₁₀ EPP groups 0·6-, 1·5-, 1·7-, and ≥2·0, but differences did not reach statistical significance. There was no obvious explanation as to why symptoms that are not found in classic lead poisoning should be increased almost as much as those that are. It was thought that these results could be biased due to the men's knowledge of the symptoms associated with lead exposure, but the possibility that they may be partly due to lead absorption cannot be excluded.     

The effects of dietary calcium and phosphorus on the retention and excretion of lead in rats.

1. Rats were given diets containing different amounts of calcium, phosphorus and lead. 2. Pb retention was greatly increased when the diets contained less Ca or P than the minimum estimated requirement of the rat. 3. The release of Pb already incorporated into the skeleton was inhibited by diets low in Ca but was not affected by diets low in P. 4. The retention of Pb given intraperitoneally was not affected by dietary Ca or P. 5. It can be concluded that dietary Ca and P influence the absorption of Pb by the gut and dietary Ca influences the metabolism of Pb in the bone. 6. There were changes in the distribution of Pb among the tissues due to changes of dietary Ca. 7. At low body concentrations, Pb probably affected skeletal growth.     

The relationship between the level of lead absorption in children and the age, type, and condition of housing

A group of 184 preschool-aged children with pretreatment blood lead concentrations (PbB) greater than or equal to 50 micrograms/dl, who received inpatient chelation therapy, were followed prospectively as outpatients for 12 months after discharge. Of these, 160 were followed for 24-30 months. Serial PbB data were analyzed according to the type of housing to which each child was discharged. Following therapy, PbB stabilized by 3 months. Thereafter, highly significant differences (P less than 0.001) existed between those living in or visiting old houses in which lead-in-paint hazards had been abated according to local ordinances (m PbB = 38.5 micrograms/dl) and those discharged to "lead-free" public housing (m PbB = 28.8 micrograms/dl) or to recently, totally gutted and renovated old housing (m PbB = 28.7 micrograms/dl). During the period of study (1978-1982), no downward trend in PbB within housing groups was found during the first 12 months of follow-up. Of the 152 children discharged to old housing, 75 had 127 recurrences of PbB greater than or equal to 50 micrograms/dl. This emphasizes the need for close and prolonged follow-up in all cases. These data indicate that substantially improved methods of detection, classification, and abatement of lead hazards must replace traditional methods if lead exposure for young children in old housing is to be reduced to an acceptable level.     

The effect of lead on mouse brain development.

Biological assimilation and transport of cadmium were determined for an arthropod food chain in an east Tennessee grassland community. Laboratory experiments demonstrated that there were no significant differences (P > 0.05) in assimilation rates (17% assimilation per day) or biological half-lives (7 days) of ¹⁰⁹Cd either as soluble nitrate or insoluble oxide in crickets under identical conditions. Field experiments demonstrated that primary consumers (crickets) accumulated ¹⁰⁹Cd much more rapidly (uptake rate = 0.55 day^?1) than did the spider predators (uptake rate = 0.08 day^?1). Equilibrium concentrations in crickets were obtained in 9 days (0.04 ppm cadmium), while equilibrium was not reached in spiders during the 30-day study. Food-chain concentration of cadmium did not occur as crickets accumulated levels of cadmium 60% of that in their vegetation food sources and spiders accumulated only 70% of the cadmium present in the cricket tissues.     

The use of the urinary excretion of delta-aminolevulinic acid as a criterion for lead absorption in industrial medicine and insurance medicine

Summary In Belgium the determination of urinary delta-aminolevulinic acid (ALA-U) in lead exposed workers has been generalised in industrial medicine. The insurance against occupational diseases also uses this criterion, amongst others, for evaluation of compensation claims. Although the insured population is very heterogeneous, the results gained on a large number of claimants for compensation are in accordance with the scientific literature on this matter. Regression comparison shows a semi-logaritmic relation with PbB. Furthermore, the expression of ALA-U in mg/g creatinine yields more valid results, mainly due to a smaller dispersion. On the basis of these regression equations, permissible limits of ALA-U of 6 mg/g creatinine and of 10 mg/g creatinine are proposed respectively for prevention and for compensation of work-incapacity in insurance medicine.     

The influence of dietary amino acids on lead absorption

Dietary supplements of about 5 g/kg of a number of amino acids increased tissue lead concentrations in newly weaned rats but decreased them in older rats. The retention of both oral and intraperitoneal lead was affected. The uptake of ²⁰³Pb by tissues was reduced when methionine was given in the diet over a period of 5 weeks or when it or ethionine was given by mouth 24 hr before the activity was measured. In the liver the fraction of the total activity found in the nuclei and mitochondria was increased by methionine, but in the kidney only the fraction found in nuclei was increased.