Extracutaneous histologic changes accompanying zinc deficiency in pups.

The extracutaneous tissues in pups fed a Zn-deficient diet were examined. Four pups were fed a Zn-deficient diet and 3 littermates were fed a Zn-adequate diet. After 5 weeks, the pups were euthanatized. Lesions found only in pups fed a Zn-deficient diet were located in the buccal mucosa, lymph nodes, spleen, and thymus. In the buccal mucosa, lesions consisted of irregular epithelial hyperplasia and disruption of epithelial cell layers. There was a marked absence of lymphocytes in the thymus and in T-cell areas of the lymph nodes and spleen.

Use of laboratory animals to define physiological functions and bioavailability of zinc.

For the past 50 years laboratory animals have been used to ascertain the metabolic bases for signs of zinc deficiency such as sharply reduced food intake, severe dermatitis, slow wound healing, delayed sexual development and function, reduced immunocompetence, severe teratogenic abnormalities, and abnormal metabolism of carbohydrate, lipid, and protein. Current evidence indicates that many of these symptoms may be consequences of inhibition of early steps in nucleic acid metabolism that lead to problems with cellular replication and growth and also that zinc plays an important role in membrane structure and function. Bioavailability of zinc to experimental animals was early shown to be reduced by plant protein diets and to be further reduced by feeding excess calcium. Current evidence indicates phytic acid in plant proteins to be a major inhibitor of zinc absorption, although food-processing methods can either increase or decrease zinc bioavailability. The inhibitory effect of phytic acid is very dependent on dietary calcium in association with phytate and zinc. Usual calcium intakes by humans are much below those demonstrated in animals to cause phytate inhibition of dietary zinc availability.

Effects of dietary phytate, calcium and magnesium levels on zinc bioavailability to rats.

Young rats were fed diets containing 12 mg Zn/kg and varied levels of sodium phytate for 21-day ad libitum feeding periods. In experiment 1, Ca levels were 0.3, 0.5, 0.8 and 1.0%, and phytate:Zn molar ratio varied between 0 and 50. In experiment 2, Ca was maintained at 0.3%, Mg levels were 0.07, 0.22 and 0.37%, and phytate:Zn molar ratios were 0, 10, 20 and 30 at each Mg level. Major response criteria were body weight gain and tibia Zn accumulation. Weight gain was not influenced by Ca level in the absence of phytate or by phytate at 0.3% Ca; it was increasingly depressed as phytate was increased and by each increase in Ca in the presence of phytate. Total tibia Zn content was decreased at the highest Ca level in the absence of phytate; increasing the phytate progressively depressed tibia Zn at all Ca levels. Mg and phytate additions did not affect weight gain. Tibia Zn tended to be depressed by Mg and by phytate but these effects were significant only at the highest levels of the combined additions. These data corroborate and extend previously published findings on Ca and phytate effects on Zn utilization and show bone Zn accumulation to be a more sensitive criterion than weight gain in this connection. They also indicate that Mg exerts a less pronounced effect on Zn utilization in phytate-containing diets than does Ca.

Bioavailability of zinc to rats from defatted soy flour, acid-precipitated soy concentrate and neutralized soy concentrate as determined by intrinsic and extrinsic labeling techniques.

The bioavailability of 65Zn from intrinsically and extrinsically labeled soy flour, acid-precipitated soy concentrate and neutralized soy concentrate was evaluated in rats. Weanling rats were fed marginally zinc-deficient diets, providing 8 ppm zinc from one of these three soy products, for 7 days. The rats then received a radioactively labeled test meal, identical in composition to the previous diet except that the soy product was either intrinsically or extrinsically labeled with 65Zn. After the test meal the rats were again fed diets the same as those consumed prior to the test meal. Whole-body retention of 65Zn at 24 hours and 12 days as well as 65Zn retained in tibias of rats given meals containing neutralized concentrate-based meals was significantly lower than for rats given meals containing the soy flour or acid-precipitated concentrate. In addition, retention of 65Zn from the extrinsically labeled acid-precipitated concentrate-based meal was significantly higher than from the same product intrinsically labeled. These findings confirm the results of previous feeding studies from which it was suggested that neutralization of soy protein concentrates reduces zinc bioavailability to the rat. In addition, the results are taken to suggest that experimental conditions may influence the validity of the extrinsic labeling technique for zinc.

Bioavailability of zinc in coagulated soy protein (tofu) to rats and effect of dietary calcium at a constant phytate:zinc ratio.

An assay was conducted with young albino rats to compare the bioavailability of zinc contained in calcium- and in magnesium-precipitated tofu to zinc supplied as the carbonate in egg white diets. Relative availability of zinc from both tofu preparations was 51% as measured by weight gain and 36-39% for log micrograms tibia zinc accumulation. In a separate experiment with zinc supplied at 9 mg/kg in all diets, the effect of increasing dietary calcium on weight gain and tibia zinc accumulation was tested. Performance of tofu-fed rats relative to zinc carbonate-fed rats at 0.4, 0.7 and 1.2% calcium was, respectively: 92, 67 and 48% for weight gain, and 70, 58 and 61 for tibia zinc content.

Tissue changes in dogs fed a zinc-deficient ration.

Six-week-old puppies fed a corn-soy based zinc-deficient diet developed lesions of parakeratosis, mild hyperkeratosis, alterations in germinal epithelium, erosions, ulcerations, vesiculation, alopecia, and inflammation of the skin. These changes were prominent in the skin of dependent regions, in areas of stretch and friction, and external contact. The epithelial lesions were reversible by adding zinc to the diet, with complete remission of external lesions by 6 weeks.

Effect of protein-induced calciuria on calcium metabolism and bone status in adult rats.

45Ca-labeled adult male rats were fed diets high in protein to determine long-term effects on calcium metabolism and bone status. Factors influencing renal excretion of calcium were examined for their involvement in protein-induced hypercalciuria. Control rats were fed a 6% casein diet. Test diets contained 6% casein plus 24% protein as lactalbumin, beef, casein, soy, egg white or gelatin. All diets were equal in Mg, P, and Ca. Collections made during the 20-week feeding regimen indicated a transient but marked calciuria (greater than or equal to 200% of control) occurring at or prior to days 56-59 by rats fed the lactalbumin, egg white, gelatin (P less than or equal to 0.001) and 30% casein (P less than or equal 0.01) diets. Soy and beef diets were not calciuric. At days 56-59, rats fed lactalbumin, 30% casein, soy and egg white exhibited significantly depressed urinary specific activity of calcium (P less than or equal to 0.001), and all rats fed test diets produced higher fecal endogenous calcium, suggesting an increased absorption. No compositional differences indicative of bone resorption were present in the femur or mandibles of any rat fed test protein, dismissing bone as the source of calciuria. End-products of protein metabolism known to chelate calcium or compete with its renal reabsorption were significantly correlated with urinary calcium; these included sulfate, oxalate and sodium.

Effect of magnesium deficiency on rat bone and kidney sensitivity to parathyroid hormone.

A series of six experiments was conducted to investigate the effects of Mg deficiency in the young rat on parathyroid hormone (PTH) activity and on response to parathyroid extract (PTE) and to endogenously produced PTH stimulated by dietary Ca deficiency. Major criteria employed were 45Ca release from pre-labeled bone and urinary excretion of cAMP. Mg deficiency was accompanied by lowered 45Ca mobilization and urinary cAMP excretion, indicating either a depression in PTH secretion or tissue insensitivity to it. Administration of PTE resulted in equivalent increases in 45Ca mobilization irrespective of Mg status but increased cAMP excretion only in Mg-adequate animals, thus indicating a depressed sensitivity of kidney to PTH in the Mg-deficient animal. In vitro response of kidney cortex from Mg-deficient animals to PTE added to incubation medium indicated no defect in the adenyl cyclase system. Endogenous stimulation of PTH by low Ca diet increased cAMP in Mg-adequate animals but not in rats with pre-existing Mg deficiency. Mg deficiency did not reduce cAMP previously stimulated by Ca deficiency.

Studies on the role of nickel in the ruminant.

Lambs were fed 6 to 7% of metabolic body weight per day of a basal purified diet low in nickel (65 ppb) or the basal diet plus 5 ppm nickel for a 97 day period in an attempt to demonstrate an essential role for nickel in the ovine. Weight gains for the entire period and digestibility of dry matter and of protein at 28 and 56 days were not different between the two groups. At 28 days, but not at 56 days, urinary nitrogen was less and percentage retention of absorbed nitrogen was greater in the supplemented lambs. Total serum proteins were higher at 56 days and serum alanine transaminase was higher throughout the experiment in the nickel supplemented lambs, but only significantly so at 56 days. When lambs were given an oral dose of 65Ni, the low nickel lambs tended to excrete more in the feces and retained less in the kidney, lung, and liver at 72 hours post dosing. The major excretory route of nickel was via the feces. The kidney retained the highest concentration of 65Ni of the organs examined.

Influence of dietary copper on lead toxicity in the young male rat.

An investigation of the influence of dietary copper (1, 5, 20 ppm) on toxicity of dietary lead (0 and 200 ppm) in the young male rat in a 4-week period indicated that as dietary copper increase so did the severity of lead toxicity. Evidence included increased lead concentration in kidney and a two- to threefold increase in the excretion of urinary delta-aminolevulinic acid. Liver copper concentration was also found to increase in rats receiving lead at the two lower copper levels. The data suggest that supplementary dietary copper doesnot lessen the severity of lead toxicity but rather exaggerates it.

Influence of dietary selenium on lead toxicity in the rat.

An investigation of the influence of dietary selenium (0.015, 0.05, 0.50, 1.0 ppm) on toxicity of dietary lead (0 and 200 ppm) in the young male rat indicated that selenium was mildly protective against the toxic effects of lead, but only up to 0.50 ppm selenium. At the excess selenium dietary level an exaggeration of lead toxicity was observed. Criteria employed to judge the effects of dietary selenium on lead toxicity included tissue lead concentration and urinary delta-aminolevulinic acid excretion. One exception to the exaggeration effect of excess selenium on lead toxicity was the protective effect of selenium on liver delta-aminolevulinic acid dehydratase activity. Since lead depressed kidney selenium concentration, lead may act as an antagonist to selenium metabolism.

Influence of dietary zinc on lead toxicity in the rat.

An investigation of the influence of dietary zinc (8, 35, 200 ppm) on the toxicity of dietary lead (0, 50, 200 ppm) in the young male rat in a seven week period indicated that as dietary zinc increased, the severity of lead toxicity decreased. Evidence included decreased lead concentration in blood, liver, kidneys, and tibias; decreased excretion of urinary delta-aminolevulinic acid; decreased accumulation of free erythrocyte porphyrins; decreased inhibition of kidney delta-aminolevulinic acid dehydrase activity; and a decrease in apparent lead absorption. Infected zinc did not afford protection against lead toxicity. The data indicate that the protective effect of zinc on lead toxicity is largely mediated by an inhibition of lead absorption at the intestinal level.

Influence of dietary Ca, Mg, and P on cyclic-AMP excretion and kidney calcification in the rat.

A series of five experiments was conducted with young male albino rats to investigate effects of various levels of dietary Ca, P and Mg on urinary cAMP excretion and kidney calcification. Urinary cAMP excretion was shown to be directly correlated with injected parathyroid (PT) hormone dose level and to be inversely associated with dietary Ca intake. Thus, cAMP excretion may be presumed to reflect PT activity in the young rat. Magnesium deficiency tended to reduce cAMP excretion, while P excess did not affect it. Each treatment induced kidney calcification. Calcium deficiency increased cAMP excretion irrespective of Mg status, although nephrocalcinosis appeared only in the Mg-deficient animals. These data support the view that nephrocalcinosis of dietary origin in the rat is not mediated by increased PT activity.