James N. Morrison

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.

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.

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.

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 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.

The effect of zinc deficiency on sheep intestinal mucin.

Abstract To examine the possible effects of zinc deficiency on mucin composition a mucin was prepared by proteolysis of sheep intestinal mucosa, and fractionated by centrifugation and ethanol precipitation. The composition of these fractions was different when the mucin was obtained from zinc-deficient and from zinc-supplemented sheep.

The effect of dietary sulphur and of castration on lead poisoning in lambs.

Abstract Castrated lambs given diets containing 200 mg lead per kg and 0·7, 2·3 or 3·8 g sulphate sulphur per kg survived for a mean time of 6, 15 and 30 weeks respectively. A few weeks before death they stopped eating and lost weight rapidly but showed no other signs of toxicity except for histological changes in the kidney. After the first few weeks tissue and blood lead contents were fairly constant and in 2 sheep alive after 40 weeks blood lead concentrations decreased. In another experiment intact male lambs were given diets containing 400 mg lead per kg and 0·7 or 3·8 g sulphate sulphur per kg. The lambs given the lowsulphur diet died within a few weeks and had anorexia, anaemia, osteoporosis and kidney lesions.

Metallothionein Concentrations in the Blood and Urine of Streptozotocin Treated Rats

The accumulation of metallothionein (MT) in tissues is influenced by changes in Zn and Cu status and also by the occurrence of various types of stress and infection. The effects of these ‘stress’ factors are mediated by changes in hormonal status; glucocorticoids, glucagon and catecholamines can, for example, induce hepatic MT synthesis. In studies of the effects of adrenal and pancreatic hormones on trace metal metabolism, Failla et al. (1985) have shown that hepatic and renal concentrations of Zn, Cu and of MT are greatly increased in rats made diabetic by treatment with streptozotocin (STZ). We have recently suggested that assay of MT in blood and urine can be used in the diagnosis of Zn deficiency (Bremner and Morrison, 1987) but before this technique can be applied in practice more information is needed on the effects of other patho-physiological states on the occurrence of MT in these fluids. It is particularly important that studies be extended to conditions where tissue MT levels are altered. It was therefore of interest to determine the effects of STZ-induced diabetes on MT levels in blood plasma and cells and in urine of rats.

Factors Influencing the Accumulation of Metallothionein in Rat Blood Cells

It has been shown by radioimmunoassay that small amounts of metallothionein (MT) are present in blood plasma and cells of normal rats. Concentrations in plasma generally increase after induction of tissue MT synthesis but little is known of the effects of nutritional and physiological factors on the occurrence of MT-I in blood cells or on its distribution among sub-populations of cells. As part of an investigation into the use of MT assays for the assessment of trace element status, we have examined the effects of zinc deficiency, of zinc and cadmium injection, of endotoxaemia and of induced reticulocytosis on the occurrence of MT-I in blood cells of rats.