Dietary Zinc Concentration Research Articles

Age, sex and reproductive status alter the severity of anorexia in zinc deficient rats

Food intake and body weight gain in rats fed a zinc-deficient diet are reported. The severity of zinc deficiency-induced anorexia was observed to be dependent upon the age, sex and reproductive status of the animal. Rapidly growing rats such as weanlings, adult males, or ovariectomized females demonstrated more rapid induction of anorexia and more severe effects on cumulative food intake and body weight gain when fed zinc-deficient diets than did slowly growing (nonpregnant female adult) rats given the same diet. These results suggest that feeding in zinc-deficient animals is not regulated by dietary zinc concentration alone, but rather is mediated by one or several as yet undefined factors.

Utilization of Zinc from Picolinic or Citric Acid Complexes in Relation to Dietary Protein Source in Rats

Young male Sprague-Dawley rats were divided in 18 groups of eight animals each and were fed ad libitum for 24 d a purified diet with 20% casein, whey protein or serum albumin as protein source. Each diet was supplemented with zinc picolinate, zinc citrate or zinc sulfate to a level of dietary zinc equal to 5 or 10 ppm. The source of zinc had no significant effect on zinc utilization with any of the three dietary proteins or at either dietary zinc concentration. With the 5 ppm Zn diet zinc concentration in the serum, but not weight gain or the zinc concentration in femur, testis or whole body was lower in rats fed the casein diet than in those fed the whey diet. Zinc concentrations in serum, femur, testis and whole body, but not weight gain, were lower in rats fed the casein diet than in those fed the serum albumin diet. With the 10 ppm Zn diet, zinc concentrations in serum, femur and whole body, but not weight gain nor zinc concentration in testis, were lower in rats fed the casein diet than in those fed either of the other diets. These results suggest that the reason for the lower utilization of zinc from cow milk in comparison to human milk may be the higher casein concentration in cow milk.

Effect of dietary copper and zinc levels on tissue copper, zinc, and iron in male rats

The interaction between dietary copper and zinc as determined by tissue concentrations of trace elements was investigated in male Sprague-Dawley rats. Animals were fed diets in a factorial design with two levels of copper (0.5, 5 μg/g) and five levels of zinc (1, 4.5, 10, 100, 1000 μg/g) for 42 d. In rats fed the low copper diet, as dietary zinc concentration increased, the level of copper decreased in brain, testis, spleen, heart, liver, and intestine. There was no significant effect of dietary copper on tissue zinc levels. In the zinc-deficient groups, the level of iron was higher in most tissues than in tissues from controls (5 μg Cu, 100 μg Zn/g diet). In the copper-deficient groups, iron concentration was higher than control values only in the liver. These data show that dietary zinc affected tissue copper levels primarily when dietary copper was deficient, that dietary copper had no effect on tissue zinc, and that both zinc deficiency and copper deficiency affected tissue iron levels.

Influence of Dietary Calcium, Phosphorus, Zinc and Sodium Phytate Level on Cataract Incidence, Growth and Histopathology in Juvenile Chinook Salmon (Oncorhynchus tshawytscha)

To determine the influence of wide variations in dietary levels of calcium, zinc and phytic acid (as sodium phytate) on growth and cataract incidence, juvenile chinook salmon held at 10–11°C were fed daily to satiation for 105 d one of nine purified diets containing one of three levels (grams/kilogram) of calcium (averaged 4.8, 17.7, 50.2), zinc (averaged 0.05, 0.15, 0.39) and phytic acid (1.62, 6.46, 25.8). Diets were formulated to have a calcium-phosphorus ratio of close to unity when considering phosphorus sources other than sodium phytate. High dietary phytic acid concentration (25.8 g/kg) depressed chinook salmon growth, food and protein conversion [protein efficiency ratio (PER)] and thyroid function, increased mortality, promoted cataract formation (zinc at 0.05 g/kg) and induced anomalies in pyloric cecal structure. Calcium at 51 g/kg (or phosphorus) exacerbated the effects of high dietary phytate and low dietary zinc on cataract incidence. Moreover, high dietary levels of calcium (48–51 g/kg) coupled with phosphorus significantly impaired the growth and appetite of low phytic acid (1.62 g/kg) groups and led to nephrocalcinosis in low and high phytic acid groups. Plasma zinc levels were directly related to dietary zinc concentration and inversely related to dietary phytic acid level. Calcium (51 g/kg) and/or phosphorus reduced zinc bioavailability when the diet concurrently contained 0.05 g zinc and 25.8 g of phytic acid per kilogram. It is concluded that zinc is essential for normal eye development in juvenile chinook salmon. Further, zinc deficiency could not be induced in chinook salmon fed diets with high ratios of calcium (or phosphorus) to zinc alone. This required the simultaneous presence of a strong mineral (zinc)-binding agent.

Copper and Zinc Absorption in the Rat: Mechanism of Mutual Antagonism

The influence that copper and zinc exert on each other’s absorption was studied by using the isolated, vascularly perfused rat-intestine system. In the first series of experiments, rats were fed for 1 wk one of nine diets, with different copper and zinc concentrations representing low, adequate and high dietary metal intakes. Copper concentrations were 1, 6 and 36 mg/kg diet and zinc concentrations were 5, 30 and 180 mg/kg. The small intestine was perfused with M199 tissue culture medium containing 6 mg/L copper and 30 mg/L zinc. Neither metal was found to significantly alter the other’s absorption. High dietary zinc increased metallothionein-bound copper but did not change the intracellular copper concentration. In the second series of experiments, the dietary copper and zinc concentrations were held at 6 mg/kg and 30 mg/kg, respectively, while the metal concentrations in the luminal perfusate were changed (from 1 to 36 mg/L and from 5 to 180 mg/L for copper and zinc, respectively). The higher copper concentrations in the perfusate increased zinc accumulation in mucosal cells and decreased the zinc transferred to the portal perfusate at the highest luminal zinc concentration. These data indicate that a competition and/or inhibition of a pathway for zinc out of the mucosal cell occurs at high luminal copper concentrations. High luminal zinc concentrations in the perfusate decreased the copper concentration in the mucosal cell cytosol and the amount transferred to the portal effluent. These results taken together indicate that a competition and/or inhibition of copper or zinc uptake into intestinal cell occurs when the luminal concentration of the respective congener is very high.

Interactions of salicylate, dietary zinc, and genetic strain in teratogenesis in rats.

The influence of dietary zinc concentration on salicylate teratogenesis was studied in Wistar and Sprague-Dawley rats. Females were fed purified diets containing 0.4, 4.5, 9, 100, or 1,000 micrograms zinc/gm diet, or a stock diet (Purina Rat Chow) from day zero to day 21 of gestation, when they were killed and the fetuses were examined. On day 9, rats were given saline or 250, 500, or 750 mg sodium salicylate/kg body weight by gavage. Increasing drug dose caused increased frequency of malformed or resorbed fetuses, while increasing dietary zinc reduced the teratogenic effects of salicylate, but in different patterns in the two strains. The teratogenic effect of zinc deficiency also varied by strain. Statistical analysis showed that the frequency of malformed fetuses was significantly affected by levels of dietary zinc or salicylate dose, and interactions of zinc X salicylate and genetic strain X zinc. Frequency of resorption was affected by strain, zinc, salicylate, and interactions of strain X salicylate, zinc X salicylate, and strain X zinc X salicylate. Frequency of abnormal sites (malformed or resorbed) was affected by strain, zinc, salicylate, and interactions of strain X salicylate, zinc X salicylate, and strain X zinc X salicylate. The results suggest that marginal zinc deficiency in certain pregnant women might increase the possibility of salicylate teratogenicity.

Dietary zinc intake and zinc concentrations of plasma, erythrocytes, and breast milk in antepartum and postpartum lactating and nonlactating women: a longitudinal study

The zinc status of a group of 23 lactating and 13 nonlactating women was assessed longitudinally from 37-wk gestation through 6 months postpartum. Dietary zinc intake was determined by chemical analysis of 3-day duplicate plate food composites. In addition, zinc concentrations were measured in plasma, erythrocytes, and breast milk. The mean dietary zinc intake of both groups of postpartum women as determined by direct analyses was 42% of the Recommended Dietary Allowances or less. The plasma and erythrocyte zinc concentrations were not significantly different between the lactating and nonlactating women. Plasma zinc concentration increased from the time of delivery to one month postpartum for both groups and did not significantly increase further through 6 months postpartum. Erythrocyte zinc decreased from delivery through 6 months postpartum for both groups. Breast milk zinc concentration decreased with the duration of lactation. The calculated zinc intake of infants from breast milk was less than 50% of the Recommended Dietary Allowances. There was no correlation of maternal dietary zinc intake or maternal plasma and erythrocyte zinc with the concentration of zinc in breast milk.

Optimal zinc requirement of lactating dairy cows based on various dose-response relationships

Dose-response relationships were established by multiple regression analysis of data from a zinc depletion-repletion study conducted with five first-lactation cows in order to estimate optimum zinc requirement. Zinc supply in the various experimental periods ranged from 6 to 436 ppm in the dry matter of the semisynthetic diet. The response criteria were the zinc concentrations in serum and milk and the activity of the alkaline phosphatase in serum. They correlated best with the reciprocal of the dietary zinc concentrations. Serum zinc also showed a close negative relationship to daily milk production (9-24 kg) and milk zinc to stage of lactation (2-21 weeks post partum). The response of the activity of the alkaline phosphatase, which was sufficiently described by simple regression to the inverse of dietary zinc concentration, was limited to a distinctly lower zinc supply range than the response of the serum and milk zinc level. The optimum zinc requirement of the cows was estimated to have been met with about 35 ppm Zn in the ration on the basis that 90% of the maximum response of the serum and milk zinc concentration was reached at this supply level. In the practical feeding situation, dairy cows should, however, be allowed 50 mg zinc per kg dry matter intake according to current recommendations in order to make certain that the physiological capacity of milk to bind zinc is sufficiently fulfilled even at highest milk production.

Effects of Dietary Zinc Levels on Zinc Concentrations in Tissues of Common Carp

Common carp always has higher zinc concentration in viscera than other carps. To determine the relationship between the dietary zinc level and zinc concentration in common carp, the fish were fed diets containing 17, 294, 1,007 and 1,974 ppm zinc for 8 weeks, and the zinc concentration in each tissue was measured. It was found that the group of fish fed 17 ppm zinc had the highest growth rate. When the dietary concentration of zinc was lower than 294 ppm, the zinc concentrations in the tissues were similar during the 8 weeks of experiment. The zinc accumulated in the fish when the dietary zinc concentration was higher than 1,007 ppm. Zinc accumulated first in the digestive tract, then in the skeletal tissues and then in skin and muscle. Common carp and silver carp were fed the same diet from hatchling till adult. The results indicated that no matter whether the feed was natural food or artificial feed containing 300 ppm of zinc or artificial feed containing 25 ppm of zinc, the zinc concentrations in common carp were several times higher than silver carp. We concluded that the fact that common carp had higher zinc concentrations than other carps was not caused by the diet, but might arise from the fact that the absorption rate of zinc was higher.zinc carp

Effect of Dietary Phytate/Zinc Molar Ratio on Growth and Bone Zinc Response of Rats Fed Semipurified Diets

In rats fed semipurified diets, bioavailability of dietary zinc was tested at different phytate/zinc molar ratios; growth and zinc in femurs were the criteria of adequacy. On diets with 10--12 ppm zinc, the growth of rats was not affected by phytate/zinc molar ratios of 12 or less if the level of dietary calcium was 0.75% but was depressed at ratios greater than 6 if the level of calcium was 1.75%. Phytate/zinc molar ratios greater than these did not depress growth if the dietary zinc concentration was at least 2.5 and 5 times the minimal requirement for growth at dietary calcium levels of 0.75 and 1.75%, respectively. At the maximum phytate/zinc molar ratio that did not depress growth, accumulation of zinc in femurs was depressed. Small increases in dietary calcium (from 0.75 to 0.87%) depressed growth of rats fed diets with 12 ppm zinc and a phytate/zinc molar ratio of 25. Preformed Zn3 and Zn6 phytate preparations were equivalent to ZnSO4.7H2O as dietary zinc sources. The data indicated that high dietary calcium per se reduced zinc bioavailability. The maximum phytate/zinc molar ratio that did not depress growth of young rats was greatly influenced by dietary calcium level and somewhat influenced by total dietary zinc concentration.

Total True Efficiency of Zinc Utilization: Determination and Homeostatic Dependence upon the Zinc Supply Status in Young Rats

Total true efficiency of zinc utilization and its component factors, true absorption and metabolic efficiency, were studied in relation to dietary zinc supply in a 15-day experiment with 36 weanling rats in six groups. After day 3, the initial supply of 18.2 ppm zinc in the diet for all groups was changed to 5.6, 10.6, 18.2, 39, 70 and 141 ppm in groups 1 to 6, respectively. During the 6-day balance period after day 9, zinc intake was proportional to dietary zinc concentration. Mean daily rates of weight gain and apparent zinc retention increased from a near zero level in group 1 to a high plateau from group 4 to 6. True absorption rate steadily rose and reached about twice that of apparent absorption in group 6. This difference in rates was due to endogenous zinc excretion. Percent total utilization and percent true absorption steadily declined from a mean of about 100 in groups 1 and 2 to nearly 15 and 30, respectively, in group 6. Metabolic efficiency, reflecting true retention of absorbed zinc, similarly declined as percent true absorption did. The major conclusion was that not only the absorptive but also the metabolic efficiency greatly contributed to zinc homeostasis and total true efficiency of zinc utilization.

Some effects of oral ingestion of cadmium on zinc, copper, and iron metabolism.

Data are presented to show that ingestion of cadmium chloride by rats at low levels leads to alteration of zinc metabolism in the liver, even though the formation of metallothionein is not evident. A dose-response relationship between amount of cadmium ingested and degree of perturbation of zinc metabolism in liver was found. Oral cadmium was shown to cause emphysema and reduce pulmonary function in male rats; the effect was less severe or delayed in onset if dietary zinc concentration was high. Interference with copper and iron metabolism was shown to occur in rats given low levels of cadmium orally. Depression of copper and iron metabolism of the rat fetus was found to occur when dams received very low doses of cadmium during gestation, even though very little cadmium passed the placental barrier.

Intestinal metallothionein and the mutual antagonism between copper and zinc in the rat

A study has been made of the mechanism of the mutual antagonism between copper and zinc in rats. Dietary zinc concentrations of up to 450 mg/kg had no effect on intestinal 64Cu absorption but 900 mg/kg caused a 40% reduction. This was associated with an increase in the mucosal uptake of 64Cu in the small intestine. This occurred mainly in the form of metallothionein and it appeared that copper displaced zinc from the protein after its synthesis had been induced by zinc. The intestinal absorption of 65Zn was decreased by 20% when the dietary copper intake was increased from 3 to 24 mg/kg. Further increases in copper intake to 300 mg/kg did not cause any additional decrease in 65Zn absorption or any change in the association of intestinal 65Zn with metallothionein. Concentrations of this protein in the intestinal mucosa were not influenced by dietary copper intake.

An Interaction between Zinc and Vitamin A in Pregnant and Fetal Rats

A possible interaction between zinc and vitamin A metabolism was studied in pregnant rats. Rats were depleted of vitamin A by feeding retinoic acid during growth. At mating, they were fed diets containing 100, 9, or 0.5 microgram/g zinc and were given orally 400, 8, or 0 microgram/kg body weight/day of retinyl palmitate. Low intake of zinc, but not of vitamin A, caused maternal body weight gain, placental weight, and fetal weight all to be low. The number of implantation sites affected and the proportion of fetuses malformed were dependent on intake of both zinc and vitamin A, and there was a significant interaction between these nutrients in regard to both of these parameters. In maternal as well as in fetal animals, plasma and liver zinc concentrations were low in groups fed low levels of zinc, but not in those given low vitamin A. Liver vitamin A values were affected by vitamin A intake but not by dietary zinc concentration. However, plasma vitamin A concentration in both maternal and fetal animals was significantly reduced by low intake of either zinc or vitamin A. There was a significant interaction between these two nutrients in regard to plasma vitamin A. These data indicate an interaction between zinc and vitamin A metabolism possibly at the level of vitamin A mobilization from the liver.

Effect of high dietary zinc upon zinc metabolism and intracellular distribution in cows and calves.

Changes in the metabolism of zinc were investigated in mature nonlactating Holstein cows and 4-mo old calves fed high but nontoxic amounts of dietary zinc. Increasing dietary zinc of calves from 42 to 642 ppm elevated the zinc content of liver and pancreas 600% and 1400%, respectively. The elevated zinc in liver and pancreas involved a substantial increase in all intracellular fractions, with by far the largest amount associated with a 10,000 molecular-weight protein in the soluble cell fraction. This zinc-binding protein may protect the cell against damage from increased zinc. A comparable increase in dietary zinc of mature cows did not affect zinc content of liver or kidney nor alter the intracellular distribution of zinc in the liver. In mature cows, homeostatic control mechanisms which regulate the zinc content of tissue are much more effective than in calves. Accordingly, mature cows probably are able to tolerate higher concentrations of dietary zinc.

The effects of dietary zinc concentration on reproduction in the rat.

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