R. B. Williams

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 ZnSO 4 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 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.

Zinc deficiency and the zinc requirements of calves and lambs.

1. The effects of changes in zinc intake on weight gain, plasma Zn concentration and the development of clinical lesions of Zn deficiency have been studies in Zn depletion and repletion studies with calves and lambs. 2. A basal diet, the principal components of which are urea, dried egg white, starch, glucose, cellulose and arachis oil has been developed for trace element deficiency studies with ruminants. 3. Weight gain ceased abruptly in both calves and lambs when either the unsupplemented basal diet was given or when Zn supplements provided only 0.05 mg Zn/kg live weight per day. Mean plasma Zn concentrations in these animals fell from pre-experiment values of between 0.8 and 1.2 μg Zn/ml to below 0.4 μg Zn/ml after 1 week on these treatments. 4. Supplements providing 0.2 mg Zn/kg live weight per day were sufficient to maintain a good rate of growth but insufficient to prevent a fall in plasma Zn. 5. Growth arrest occurring within 2 weeks and a rapid fall in plasma Zn occurring within 1 week after Zn supplements were withheld from calves and lambs that had previously received 0.7 mg Zn/kg live weight per day for 6 and 14 weeks respectively indicated that these species have only a limited capacity to store Zn in a form that can be utilized during periods of inadequate Zn intake. 6. Tentative estimates are presented of the Zn requirements of calves maintained on this type of basal diet and the influence of ration composition of Zn availability is discussed. 7. The possible value and the limitations of plasma Zn determination as an aid to the field diagnosis of Zn deficiency are considered.

The effects of early zinc deficiency on DNA and protein synthesis in the rat

1. The effects of early zinc deficiency on DNA and protein metabolism of the liver, kidneys, testes and spleen of the young rat were studied. The investigations were carried out in two phases: before food consumption and growth were affected, and afterwards. 2. The incorporation of [ 3 H]thymidine into DNA was markedly affected by differences of less than a week in the age of the rats. 3. Zn deficiency significantly reduced the incorporation of [ 3 H]thymidine into DNA of liver, kidneys and spleen before growth and food consumption were affected. The degree of inhibition was of the order of 50% in the first 5 d. A similar but non-significant trend was observed for the testes. 4. The incorporation of [ 3 C]lysine into protein was not significantly affected in liver and testes during the initial period of Zn deficiency; the incorporation into kidneys and spleen was significantly inhibited but the magnitude of the effect was only of the order of 20% in 5d. 5. One week after the start of the second phase, the concentration of DNA in liver, testes, and spleen of Zn-deficient animals was not significantly different from that in pair-fed controls. The DNA content of the kidneys was significantly reduced by the deficiency hut only to 97% of that in pair-fed animalsgiven the Zn-supplcmenteddiet. The incorporation of [ 3 H]thymidine into DNA was not significantly different between deficient and control groups in any of the four organs investigated.

The effect of pregnancy and lactation on the absorption of zinc and lysine by the rat duodenum in situ

1. The absorption of zinc by the duodenum of the rat was greatly enhanced at late stages of pregnancy and during lactation. 2. During pregnancy no increase in lysine uptake could be demonstrated, but during lactation, when further increases in Zn absorption occurred, uptake of lysine was increased. 3. The increased absorption of Zn at different stages of pregnancy and lactation appeared to be related to the demand made by the developing foetuses and post-natal offspring.

The effects of pregnancy and lactation on copper and zinc retention in the rat

1. The accretion of copper and zinc in maternal tissues, conception products and postnatal offspring of the rat was determined at different stages of pregnancy and lactation. 2. Equations relating the weight of the bodies of the developing young and of the amounts of Cu and Zn in them to the time that has elapsed since conception showed that, early in pregnancy, the specific rates of accretion of Cu or Zn were greater than that of weight, but declined more rapidly as development continued. The instantaneous rates of accretion of both metals rose throughout pregnancy but only that of Cu continued to increase during lactation. 3. The amount of Cu in the maternal body rose significantly during pregnancy and declined thereafter, but relatively small changes in its Zn content occurred. 4. The results are discussed in relation to the relative demands for these metals during pregnancy and lactation.

The accretion of copper and of zinc by the foetuses of prolific ewes.

1. The amounts of copper and zinc in the foetuses of ewes carrying from one to four lambs were measured at different stages of gestation and estimates were made of the amounts of these metals in their livers. 2. The accretion of Cu and Zn could be described by growth equations of the Gompertz form, from which could be derived estimates of the instantaneous and fractional rates of deposition of these metals in the foetal body. 3. Between the 80th and 144th day of gestation the instantaneous rates of deposition of the metals increased exponentially, and at the end of pregnancy were calculated to be 0.24 and 2.0 mg Cu and Zn/d respectively in the triplet lamb foetus. The corresponding total accretions were estimated to be 10 and 69 mg respectively. 4. The fractional rates of live-weight gain and of deposition of Cu were similar and decreased at similar rates; that of Zn deposition decreased much more slowly. 5. The proportion of whole-body Cu estimated to be in the liver was always greater than 50 %. The amount of Zn in the liver remained constant and contributed 72 % of the total body Zn at 80 d but only 8 % at 144d. 6. The relative amounts of Cu and of Zn accrued per unit body-weight gain were not constant during the development of the foetus. As foetal numbers increased the amounts of each metal deposited in the foetus decreased more rapidly than did foetal weight. 7. The results are discussed in relation to the demands for Cu and Zn during pregnancy in sheep.

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

Since the initial demonstration by Todd, Elvehjem & Hart (1934) that zinc is essential for the nutrition of the rat, numerous studies have been made to elucidate the biochemical roles played by this element in this and other species. Almost without exception such studies have been conducted at the intermediate or terminal stages of deficiency as defined by Williams & Chesters (1970) and thus may have included effects which could have been secondary consequences of deficiency. I n the belief that the cessation of growth which occurs within about 4-5 d after introducing the rat to a low-Zn diet (Williams & Mills, 1970) is not the result of any instantaneous alterations in biochemical or physiological mechanisms at that time, work at this Institute on Zn deficiency has, to a large extent, been devoted to investigating those effects which occur before growth ceases. The experiments reported here fall in this category. Alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3 . I . 3 . I ) derived from bacteria or various mammalian tissues has been shown to contain Zn (Mathies, 1958; Engstrom, 1961 ; Trubowitz, Feldman, Morgenstern & Hunt, 1961 ; Plocke, Levinthal & Vallee, 1962), and in this connexion Hove, Elvehjem & Hart (1940), Kfoury, Reinhold & Simonian (1968) and Luecke, Olman & Baltzer (1968) have shown that in Zn-deficient rats there is a reduction in intestinal alkaline phosphatase activity compared with that in Zn-supplemented controls. It was of interest to know whether this effect was an early manifestation of the Zn-deficiency state and, if so, how the reduction in activity of this enzyme was related to the depressed food intake and the cyclical pattern of food consumption observed in the Zn-deficient rat (Williams & Mills, 1970). Alkaline phosphatase of certain tissues has been shown to have inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6. I . I) activity (Cox & Griffin, 1965; Moss, Eaton, Smith & Whitby, 1967; Fernley & Walker, 1967). Inorganic pyrophosphate is released during the course of many reactions in major pathways of

An apparatus for the regulation of the food supply to rats.

1. An apparatus is described for supplying small amounts of food to rats uniformly and continuously. 2. The apparatus consists of a Perspex disc carrying a groove containing food, which is rotated once each day by an electric motor. Access of rats to the food is restricted by suitably placed baffles.

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.

A note on the estimation of nitrogen retention in chicks by body analysis and balance methods.

I. In a balance study with young chicks estimates of nitrogen retention were made by a balance method and by a body analysis method. 2. N retention appeared to be about 15 % greater by the balance method when no allowance was made for N in alimentary tract contents. Allowance for tract contents reduced the difference to about 13 %. 3. Only about one-third of the discrepancy could be accounted for in terms of the possible sources of N loss investigated. 4. About a quarter of the difference was due to loss of N on drying the droppings before analysis and another tenth to loss of N on freeze-drying minced chick tissues. 5. No appreciable loss of ammonia could be detected from chickens and excreta under conditions prevailing in the balance trial. The efficiency of digestion of feathers, uric acid and droppings from birds appeared to be complete by the Kjeldahl method employed. 6. A difference of about 8 % could therefore not be explained.