J. Quarterman

The influence of high dietary calcium and phosphate on lead uptake and release

The effects of calcium and phosphate supplements on the retention of dietary lead and the loss of lead from the body were studied in young rats. There were three experiments in which rats were given a diet containing 200 or 400 micrograms of lead/g for 3 or 6 weeks. The diet contained adequate calcium and phosphate. Calcium and phosphate supplements were given alone or together. Lead uptake after a period of lead feeding was measured by analysis of the whole gut-free carcass. Lead loss was measured by a similar analysis after the rats had received diets containing lead and then diets free of lead. The uptake of lead from the diet was reduced by about half when either dietary calcium or phosphate or both was doubled. The rate of release of body lead was decreased by calcium supplementation.

Effects of dietary phytic acid on lead and cadmium uptake and depletion in rats

Rats were given a semipurified diet supplemented with phytate (10 g/kg) or calcium (6 g/kg) and lead (200 mg/kg) or cadmium (5 mg/kg) for 4 weeks. Addition of phytate or calcium reduced the accumulation of lead in bone (P less than 0.001) and in blood and liver samples (P greater than 0.05). The greatest inhibition of tissue lead retention was evident when phytate and calcium were fed together. Cadmium accumulation was measured in the liver and kidney and was increased (P less than 0.05) by the addition of calcium. Phytate inhibited the increase in tissue cadmium promoted by calcium supplementation but did not otherwise influence tissue cadmium levels. In a further experiment, weanling rats were given diets supplemented with cadmium (5 mg/kg) or lead (200 mg/kg) for 4 weeks, and the accumulation of these elements in the body tissues was estimated in some animals. A phytate-supplemented (10 g/kg) or phytate-free semipurified diet (free of lead and cadmium) was then given to the remaining rats for 4 weeks. Phytate supplementation was found to have no significant effect on the rate of loss of lead or cadmium from tissues.

The effects of dietary lead content and food restriction on lead retention in rats

Abstract The effects of restricted food intake and of various dietary lead contents on lead retention 1 were studied in young rats. In three experiments the rats were given either unrestricted or restricted access to diets providing 200 or 400 mg lead/kg for 3 or 6 weeks. At the end of the experiments a sample of blood was taken and the rats were ashed. Lead was determined in blood and ash from the carcass. Food restriction always increased the retention of lead but not always the lead content of blood or carcass. The retention of lead was similar when the diet was supplemented with 50, 200 or 400 mg lead/kg. Lead supplementation at 200 or 400 mg/kg reduced food intake and growth but did not affect food conversion ratios. Blood lead was related to the rate of ingestion of lead. The effect of food restriction in reducing lead retention should be taken into account in interpreting the effects of lead exposure accompanied by dietary conditions which reduce appetite or food supply.

Effect of zinc deficiency and zinc supplementation on adrenals, plasma steroids and thymus in rats.

Abstract Weanling rats were given diets deficient in or supplemented with zinc. Within a few weeks there were increases in the weight of the adrenal glands and in the concentration of cholesterol and 11-hydroxycorticosteroids in the adrenal glands of the zinc deficient animals. The decrease in cholesterol concentration due to ACTH administration was greater in zinc-deficient than in supplemented rats. After four weeks on the zinc-deficient diet rats had smaller thymus glands than zinc-supplemented rats but zinc-deficient diets had no such effect on adrenalectomised rats. The addition of 2 mg zinc/ml drinking water had no effect on adrenal weight or thymus weight but increased plasma 11-hydroxysteroids after 30 days. The possible connection between zinc intake and resistance to injury and disease is discussed.

The effect of dietary calcium and phosphate on lead poisoning in lambs.

Abstract Thirty wether lambs were given diets which contained 400 mg lead per kg and differed in their calcium, phosphorus and sulphur contents. When the diet was low in calcium or sulphur but adequate in the other major minerals the lambs stopped eating, rapidly lost weight and died within 5 weeks. When the diet was supplemented with all three minerals or was low in phosphorus they survived for up to 10 months. The only signs of lead toxicity were anorexia and weight loss. Blood, liver and frontal bone biopsy samples were taken at intervals. The lead content of these tissues rose during the first few weeks and thereafter remained fairly constant. The lead content of other tissues was measured after slaughter but only that of the kidney was related (inversely) to the length of survival of the lambs. The results show that the toxicity of a diet containing lead was greatly influenced by the major mineral composition of the diet but the lead content of the tissues, except the kidney, was not related to the severity of the toxicity after the first few weeks of exposure.

The effect of age on the absorption and excretion of lead

The retention (the proportion of ingested or administered lead found in the carcass at slaughter) of lead in the carcass and tissues of rats given 203Pb intraperitoneally or by mouth was measured over a period of a few days at 3-month intervals for 9 months from weaning. Total carcass retention of 203Pb administered intraperitoneally reached a minimum at 6 months of age, but the retention of 203Pb in blood, liver, and kidney changed little with time. When 203Pb was given by mouth, the fraction of the dose absorbed and the fraction retained in the carcass reached a minimum at 6 months, but the recovery in the tissues continued to decrease up to the end of the experiment. The addition of 20 mg of lead/kg of diet had no consistent effect on the metabolism of 203Pb.

Dietary fibers and heavy metal retention in the rat

The metal-binding capacities of some gel-forming polysaccharides and other substances have been investigated in vitro in an attempt to relate their metal-binding properties to the retention of dietary Pb and Cd in vivo. In equilibrium dialysis systems, aqueous solutions of alginic acid, pectin, agar, and carrageenan (1 g fiber/100 ml) all bound Pb and Cd to varying degrees. Alginic acid had the greatest binding capacity for Pb (50 micrograms Pb bound/mg fiber) and carrageenan for Cd (9.3 micrograms Cd bound/mg fiber). Addition of any one of these fibers, or indulin or glucuronic acid to the diet increased the tissue retention of one or both of the metals. Only cellulose supplementation reduced the retention of both Pb and Cd. Carrageenan decreased that of Pb and increased that of Cd. In another experiment alginic acid was shown to increase Pb retention in rats even when present at fairly low dietary concentrations (1 g/kg).

Dietary protein and lead retention

The effects of dietary protein content on lead retention were studied in young rats. In experiments lasting between 3 and 6 weeks, rats given diets containing lead and 20% casein were fed ad libitum or were pair fed with rats given diets containing 6.5 or 7.5% casein. Among rats given 20% casein, lead retention was inversely related to growth rate. A reduction of dietary protein either had no effect or reduced lead retention. In other experiments lasting 4 days and using 203Pb, given orally or intraperitoneally, the recovery of isotope in the gutfree carcass was unaffected or reduced by a reduction in dietary protein. Blood and liver lead often increased when kidney and carcass lead decreased in response to a reduction of dietary protein. Conflicting observations on the effect of low-protein diets on lead retention may thus be due to opposing effects of low dietary protein and decreases of growth rate and to different responses of different tissues.

The production of zinc deficiency in the guinea pig.

A diet which contained less than 1 microgram Zn per g was eaten readily by guinea pigs. No signs of zinc deficiency were produced unless the animals were deprived of access to zinc-supplemented solid food from birth and were maintained on grid floors to prevent coprophagy or ingestion of sawdust bedding material. At an early stage of deficiency, plasma zinc concentration, food intake and growth were reduced and large regular variations of food intake (food cycling) were observed. More severe deficiency produced decreases in the zinc content of other tissues and characteristic epidermal lesions. The requirement of guinea pigs for zinc for growth is probably about 2.5 micrograms per g feed which is much lower than for calves, rats and pigs.

The influence of dietary amino acids on lead absorption.

Abstract 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.