The effects of zinc deficiency on pancreatic carboxypeptidase activity and protein digestion and absorption in the rat

Effects of Elevating Zinc Supplementation on the Health and Production Parameters of High-Producing Dairy Cows

This study's objective was to determine the effects of increasing the dietary added zinc (Zn) on the milk production, milk somatic cell count (SCC), and immunoglobulin and antioxidant marker concentrations in the blood of dairy cows. Twelve Holstein cows (67 ± 2.5 days in milk) were assigned randomly to (1) a diet containing Zn-methionine at 76 mg/kg of DM (CTL) or (2) CTL top-dressed with about 21 mg/kg of DM extra Zn-methionine (+Zn) for 70 d. The concentrations of reduced (GSH) and oxidized (GSSG) glutathione, malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), and immunoglobulins in the blood were measured on d 0, 35, and 70. Compared to CTL, +Zn decreased the dry matter intake (DMI) throughout the trial and the milk yield (MY) during the first phase of feeding (0-35 d). It, however, increased the milk yield during the last phase (36-70 d). The +Zn tended to have lower and greater milk protein yields than CTL during the first and last feeding phases, respectively. The +Zn tended to decrease the SCC and was associated with lower plasma GSH: GSSG and lower serum SOD concentrations relative to CTL. The +Zn did not affect the immunoglobulins, MDA, or CAT. Despite the early DMI and MY reduction, the prolonged Zn-methionine supplementation at about 100 mg/kg of DM improved the milk yield, possibly as a result of the improved udder health of dairy cows.

Zn metabolism of monogastric species and consequences for the definition of feeding requirements and the estimation of feed Zn bioavailability

A major goal of mineral nutrition research is to provide information of feed zinc (Zn) utilization efficiency and gross Zn requirements as affected by changing rearing conditions. This can be achieved only by applying precise experimental models that acknowledge the basic principles of Zn metabolism. This review article summarizes the most important aspects of Zn homeostasis in monogastric species, including molecular aspects of Zn acquisition and excretion. Special emphasis is given to the role of the skeleton as well as the exocrine pancreas for animal Zn metabolism. Finally, we discuss consequences arising from these physiological principles for the experimental design of trials which aim to address questions of Zn requirements and bioavailability.

Subclinical zinc deficiency impairs pancreatic digestive enzyme activity and digestive capacity of weaned piglets

This study investigated the effects of short-term subclinical Zn deficiency on exocrine pancreatic activity and changes in digestive capacity. A total of forty-eight weaned piglets were fed ad libitum a basal diet (maize and soyabean meal) with adequate Zn supply (88 mg Zn/kg diet) during a 2-week acclimatisation phase. Animals were then assigned to eight dietary treatment groups (n 6) according to a complete randomised block design considering litter, live weight and sex. All pigs were fed restrictively (450 g diet/d) the basal diet but with varying ZnSO4.7H2O additions, resulting in 28·1, 33·6, 38·8, 42·7, 47·5, 58·2, 67·8 and 88·0 mg Zn/kg diet for a total experimental period of 8 d. Pancreatic Zn concentrations and pancreatic activities of trypsin, chymotrypsin, carboxypeptidase A and B, elastase and α-amylase exhibited a broken-line response to stepwise reduction in dietary Zn by declining beneath thresholds of 39·0, 58·0, 58·0, 41·2, 47·5, 57·7 and 58·0 mg Zn/kg diet, respectively. Furthermore, carboxypeptidase B and α-amylase activities were significantly lower in samples with reduced pancreatic Zn contents. Coefficients of faecal digestibility of DM, crude protein, total lipids and crude ash responded similarly to pancreatic enzyme activities by declining below dietary thresholds of 54·7, 45·0, 46·9 and 58·2 mg Zn/kg diet, respectively. In conclusion, (1) subclinical Zn deficiency impaired pancreatic exocrine enzymes, (2) this response was connected to pancreatic Zn metabolism and (3) the decline in catalytic activity impaired faecal digestibility already after 1 week of insufficient alimentary Zn supply and very early before clinical deficiency symptoms arise.

Zinc: health effects and research priorities for the 1990s

This review critically summarizes the literature on the spectrum of health effects of zinc status, ranging from symptoms of zinc deficiency to excess exposure. Studies on zinc intake are reviewed in relation to optimum requirements as a function of age and sex. Current knowledge on the biochemical properties of zinc which are critical to the essential role of this metal in biological systems is summarized. Dietary and physiological factors influencing the bioavailability and utilization of zinc are considered with special attention to interactions with iron and copper status. The effects of zinc deficiency and toxicity are reviewed with respect to specific organs, immunological and reproductive function, and genotoxicity and carcinogenicity. Finally, key questions are identified where research is needed, such as the risks to human health of altered environmental distribution of zinc, assessment of zinc status in humans, effects of zinc status in relation to other essential metals on immune function, reproduction, neurological function, and the cardiovascular system, and mechanistic studies to further elucidate the biological effects of zinc at the molecular level.

Zinc-deficient diet impairs adaptive changes in the remaining intestine after massive small bowel resection in the rat

An investigation was conducted on the influence of the presence of zinc in an elemental diet on the mucosa of residual intestine after massive small bowel resection. A total of 34 male Sprague-Dawley rats were divided into five groups: control animals (n = 10) were killed after overnight fasting; a second group (n = 14) underwent massive small bowel resection preserving 10 cm of terminal ileum, and the third group (n = 10) underwent sham operation. Animals in the second and third groups were fed either a commercially available elemental diet or a zinc-deficient diet for 2 weeks; they were then killed. In animals receiving the zinc-deficient diet, a significant decrease (P < 0.05) was noted in plasma zinc and total protein, and in mucosal wet weight (duodenum), thickness (duodenum and ileum), and protein (duodenum) and DNA (duodenum) content. Mucosal sucrase and maltase specific activities in the duodenum and ileum fell but diamine oxidase levels did not. These results suggest that zinc plays an important role in intestinal adaptation in the rat, and indicate that this trace element is essential for intestinal mucosal preservation in this animal.

The effect of dietary zinc depletion and repletion on rats: Zn concentration in various tissues and activity of pancreatic gamma-glutamyl hydrolase (EC 3.4.22.12) as indices of Zn status

Unlike severe zinc deficiency, marginal Zn deficiency is difficult to identify in rats because no reliable indicator of suboptimal Zn status is currently available. We have previously observed reduced pancreatic gamma-glutamyl hydrolase (EC 3.4.22.12) activity and impaired pteroylpolyglutamate absorption in Zn-deficient rats. In the present study the effect of Zn depletion and repletion on the Zn concentration of various tissues and on the activity of this enzyme was investigated. The objective was to determine the sensitivity of these variables to Zn depletion and to evaluate their usefulness as indices of Zn status. Male Wistar rats (about 180 g), maintained from weanling on a purified Zn-adequate diet, were randomly allocated into twelve groups. A pretreatment control group was killed immediately. The remaining eleven groups were fed on a Zn-deficient diet and a group killed daily for 7 d (Zn-depleted groups). The remaining four groups were re-fed the Zn-adequate diet and a group killed daily (Zn-repleted groups). On analysis, pancreas and spleen Zn levels responded most rapidly to reduced Zn intake, followed by tibia, liver, kidney and plasma. Zn concentration was maintained in testes. Reduced plasma folate levels were also observed. A significant reduction in pancreatic gamma-glutamyl hydrolase activity before the depletion of many tissue Zn stores confirms the Zn sensitivity of the enzyme. It was concluded that future investigation into the inter-relationship between Zn and folate metabolism may be useful in identifying a sensitive, biochemical index of Zn status.

The effect of zinc deficiency on the body composition of rats

Body composition and the levels of some plasma metabolites were measured in zinc deficient and control rats with the aim of assessing the nature of the metabolic defects resulting from zinc deficiency. Two experiments, lasting 15 and 20 d, were carried out using 52 immature rats. Zinc deficient animals were fed a diet of 1-2 mg Zn/kg. Pair fed and ad libitum control rats received the same diet with 100 ppm zinc added to the drinking water. Feed intake and growth rate were measured, and the carcasses were analyzed for protein, fat, and ash. In each experiment, a group of rats were killed on d 1 to provide pretreatment values and to allow for estimates of net deposition of carcass components. Lactate, urea, and zinc were assayed in plasma, as well as zinc concentration in carcasses and liver. The main effect of zinc deficiency was to reduce feed intake and efficiency of feed conversion, resulting in a reduced proportion of carcass fat. However, when adjustments were made for difference in body wt because of the reduced feed efficiency, zinc deficiency per se resulted in an increase in the proportion of fat in the carcass. Plasma lactate concentration was unchanged, but urea concentration increased in both pair fed and zinc deficient rats relative to ad libitum fed control animals. The results indicate that a defect in protein synthesis and an increase in energy expenditure, perhaps resulting from increased protein turnover, underlies the reduced growth and efficiency of feed conversion of zinc deficiency.

Pancreatic acinar cell function and morphology in rats fed zinc-deficient and marginal zinc-deficient diets

The prevalence of marginal zinc nutriture in several populations of people in this country and the lack of reports on the effect of marginal zinc nutriture in experimental animals prompted us to look at pancreatic acinar cell function and morphology in rats fed a zinc-deficient diet ad libitum: 4 and 50 ppm zinc-supplemented diets in amounts isocaloric to a zinc-deficient diet and Rodent-Blox fed ad libitum for a period of 49 +/- 1 (SEM) days. Because of a diminished rate of energy expenditure in zinc-deficient rats, animals receiving 50 ppm zinc-supplemented diets were offered less food, resulting in decreased body weight and pancreas weight, DNA, RNA, total protein, lipase, amylase, and secretion of protein. Specific changes due to zinc deficiency included (a) further decrease in body weight and (b) increase in content, specific activity, and secretion of lipase. Both the size and volume fraction of zymogen granules were reduced in zinc deficiency. The lumina of acinar and small ducts were collapsed with paucity of secretion products. Zinc deficiency may therefore lead to a defect in discharge mechanism. A further reduction in volume fraction of zymogen granules in the 4 ppm zinc-supplemented group was associated with increased secretion of serine proteases (trypsinogen and chymotrypsinogen), which constitute approximately 46% of total secretory protein in the pancreas under normal dietary conditions. This indicated an accelerated discharge due to an unknown mechanism. Changes in the secretion of digestive enzymes in the present study simulated ethanol-induced secretory alterations that were previously observed. Because abnormal zinc nutriture and chronic alcoholism are commonly associated, it is speculated that zinc deficiency may play a role in the ethanol-induced secretory alterations.

Stimulation of bile-pancreatic zinc, protein and carboxypeptidase secretion in response to various proteins in the rat

The objective of this study was to determine the rate of bile-pancreatic secretion of zinc, protein and carboxypeptidase (CP) in response to three different dietary proteins, egg white (EW), soy protein isolate (SPI) and casein. The infusion of protein into the duodenum stimulated a significant increase in the secretion rate of zinc, protein and CP in bile-pancreatic juice. There was a high degree of correlation between the concentration of zinc and enzyme activity (CPA and CPB) in bile-pancreatic juice indicating that zinc in bile-pancreatic juice is associated with CP activity. The average secretion rate of zinc, protein and CP during the 1-h period after infusion of protein was significantly greater after SPI infusion than after casein. The bile-pancreatic secretion rate of protein, zinc and CPB in response to EW infusion was consistently intermediate between SPI and casein and did not differ statistically from either. Only CPA secretion rate was significantly greater after EW than after casein. Differences in protein digestibility appear to account for the greater pancreatic response to SPI, and this factor may be important in understanding the effect of protein source on zinc bioavailability.

Effects of zinc deficiency on the distribution of membrane-coating granules in rat buccal epithelium

Nutritional zinc deficiency causes consistent excessive cell proliferation in the epithelium of the buccal mucosa. The number per cell and the intracellular location of membrane-coating granules in this epithelium were investigated in male rats placed at weanling age for a 4-week period on a diet containing 1.2 ppm of Zn and in their pair fed controls. Membrane-coating granules were identified on electron micrographs following their demonstration in thin sections by the use of an alkaline bismuth technique. Counts of membrane-coating granules in the first 4 rows of spinous cells and the last 4 rows of granular cells showed that in the zinc-deficient group (1) the total number of granules per cell was increased; (2) the proportion of granules displaced to the cell periphery was decreased in favor of a higher proportion persisting in the center and (3) there was a marked reduction in number and proportion of granules positioned near the superficial cell membrane. The greater uniformity in the distribution of the granules in the hyperplastic-hypertrophic epithelium of the zinc deficient group suggests weakening of the surface-oriented polarity characteristic of the control tissue.

Lysosomal stability, superoxide dismutase and zinc deficiency in regenerating rat liver

1. Lysosomal stability was slightly increased in regenerating livers from rats receiving a zinc-deficient (less than 0.5 mg/kg) diet for 10 d before surgery. 2. The activity of superoxide dismutase (EC 1.15.1.1) was significantly reduced in the same tissues. 3. The results do not support the view that increased lysosomal fragility represents a major biochemical consequence of nutritional Zn deficiency in animals.

The enhancement by dietary zinc deficiency of the susceptibility of the rat duodenum to colchicine

1. The incidence of colchicine-induced lesions in the germinal epithelium oof the rat duodenum was studied in young rats in an early stage of zinc deficiency and in their pair-fed controls. At both dose levels of colchicine used, a marked increase in the amount of cell damage was observed in the duodenum of Zn-deficient rats as compared with the pair-fed, control (Zn-supplemented) rats. 2. No statistical interaction between Zn and colchicine was demonstrable, and no lesions were found in the duodenum of animals that had not been treated with colchicine. 3. The results are discussed in relation to the effects of Zn deficiency in animals and the possible involvement of Zn in the maintenance of the integrity of microtubular structures.

Chronic zinc deficiency syndrome in a beer drinker with a Billroth II resection

A 51-year-old woman, addicted to beer for several years, developed chronic zinc deficiency which caused severe mental impairment, a poor general condition with edema and diarrhea, widespread eczema craquelé and loss of hair. Laboratory tests showed a significantly lowered serum zinc concentration, microcytic anemia, an inversed serum albumin/gamma-globulin ratio and a decreased serum thyroxine. Two years earlier, her external pancreatic function had been found severely impaired. Following oral therapy with zinc sulfate 0.2 g X 3R, daily, the patient's mental and physical condition totally changed. In two weeks serum zinc was within the normal range, while hemoglobin concentration, serum proteins, serum thyroxine became normal in 4-8 weeks.

[Effect of zinc deficiency on the digestibility and utilization of nutrients]

Weaned male rats were used in a metabolic trial to investigate the digestibility of dry matter, crude protein, ash and energy, the energy and N balances and the rates of zinc absorption and zinc retention under conditions of zinc deficiency. 2X8 experimental animals were kept in separate metabolism cages for 6 periods each lasting 5 days. The animals received a semisynthetic zinc-deficient diet (casein + starch + sucrose) containing only 1.0 mg Zn per kg of dry matter (zinc-deficient group fed ad libitum) or plus 49 mg Zn per kg of dry matter (pair-fed control group). The mean intake of dry matter was 2-3 g per day/animal. 2.9 g of food were necessary to produce 1 g of weight increase in the deficient animals and 1.4 g in the controls. The rate of apparent zinc absorption was always clearly negative in the Zn-deficient group. In the control group apparent zinc absorption decreased from 60% to 27% in the course of the trial while zinc retention decreased from 51% to 10%. During zinc deficiency the rates of both faecal and absolute renal Zn excretion were found to be greatly reduced. The proportion of renal zinc excretion relative to total excretion averaged 60% in the experimental group as compared to 17% in the controls. No significant differences were found in the digestibility data of gross energy. Nutrient digestibility (%) was significantly reduced under conditions of Zn deficiency (data for the control group given in brackets): 92,6 (94.0) for dry matter; 93,2 (94.1) for organic matter; 93.3 (96.2) for crude protein and 76.6 (90.8) for crude ash. Similarly, N retention data, in Zn-deficient animals, declined from 30.5% to 14.7%, and metabolizable energy decreased from 88.7% to 85.6%. The differences obtained are not sufficient, however, to account for the clearly increased food requirements observed in zinc-deficient animals. Thus, considerable disturbances have to be assumed to occur in the processes of intermediary nutrient utilization.

Malate dehydrogenase and glucose-6-phosphate dehydrogenase activity in livers of Ni-deficient rats

In experiments using rats it was shown that inadequate dietary supply of Ni reduces growth and lowers the erythrocyte count, hematocrit and hemoglobin level in blood, that the Ni supply affects the trace element content of iron, copper and zinc in various body organs, and that the absorption of iron is greatly impaired by Ni deficiency. For further biochemical criteria on the essentiality of nickel, the activities of two dehydrogenases, malate dehydrogenase and glucose-6-phosphate dehydrogenase, were measured in liver homogenates from two generations of rats at 30 and 50 days of age. In the 30-day-old rats of both the F1 and F2 generation, the activity of the malate dehydrogenase fell to about two-thirds the level of control animals. In the liver of the 50-day-old rats the activity of this enzyme was about the same in deficient animals as in the controls. The activity of glucose-6-phosphate dehydrogenase of Ni-deficient rats was reduced by 85% in the F1 generation and by 56% in the F2 generation at 30 days of age as compared with control levels. In 50-day-old rats the activity had fallen to half the level of control animals at 30 days of age. At the age of 50 days, there was no significant difference between the deficient and the control groups of either generation.

The effect of available dietary zinc on the utilization of protein by the chick and Japanese quail

1. Chicks and quail (Coturnix japonica) were used in the measurement of net protein utilization and true digestibility of nitrogen of isolated soya-bean protein and a mixture of casein and gelatin in zinc-deficient diets.

2. The net protein utilization values for both protein sources were increased when the diets were supplemented with Zn or with the disodium salt of ethylenediaminetetra-acetic acid, as was the true digestibility of nitrogen of the isolated soya-bean protein.

Intestinal alkaline phosphatase and inorganic pyrophosphatase activities in the zinc-deficient rat

1. The effect of zinc deficiency on the activities of rat duodenal alkaline phosphatase and inorganic pyrophosphatase has been investigated.

2. Zn deficiency adversely affected the activity of these enzymes before growth rate and food intake were reduced.

3. The level of food intake was without effect on the activity of alkaline phosphatase but markedly influenced that of inorganic pyrophosphatase.

4. The relevance of changes in the activities of Zn-dependent intestinal enzymes to the food intake of Zn-deficient rats is discussed.

The experimental production of zinc deficiency in the rat

1. Techniques for the preparation of a semi-synthetic basal diet suitable for the rapid production of zinc deficiency in the rat are described. The complete diet usually contains between 0.6 and 0.9 ppm Zn.

2. When the unsupplemented diet was fed to weanling rats, growth arrest occurred after 4–5 d; when supplemented with ZnSO4 to provide 12 or 20 ppm Zn, the rate of growth of rats was similar to that attained in animals given a conventional stock colony diet providing 83 ppm Zn. A study of relationships between dietary Zn concentration and weight gain in 21 d suggested that the Zn requirement of male and female rats for growth on this diet is approximately 12 ppm.

3. The development of Zn deficiency on diets providing < 1 or 3 ppm Zn was accompanied by poor food consumption and the development of a characteristic cyclic pattern of intake. A significant decline in the variability of daily food intake was observed when the diet was supplemented with Zn to provide 6, 9 or 12 ppm.

4. Studies of the influence of dietary Zn content upon changes in the Zn content of a range of tissues and upon whole-body Zn retention are reported.

5. The above findings are discussed in relation to the problem of defining the severity and duration of Zn deficiency in animals used for studies on the nature of the metabolic role of Zn.