A critical physiological role of zinc in the structure and function of biomembranes

Effect of zinc on neuronal activity in the rat forebrain

Zinc ions, which are unevenly distributed in the CNS and can be released from nerve terminals, have been implicated as causative agents in epileptogenesis. The present study has shown that intraventricular administration to anesthetized rats causes seizure activity of the ECOG and convulsions. Since the manner in which zinc influences neuronal activity and triggers convulsions is unclear, studies were also made of its effect on spontaneous and evoked activity in the rat forebrain. It was found that iontophoretic application of zinc to cortical neurons causes slow and often prolonged increases in firing rate, usually accompanied by bursts of high frequency discharge in just under half the studies. Another cation, barium, evoked excitatory responses of a similar type and a reduction in potassium permeability may underlie the effects of both cations. In contrast, calcium, magnesium, manganese and cerium caused short duration depressant effects. The depression induced by calcium, but not by the other cations, could be blocked by zinc. Similarly, in the hippocampus zinc depressed calcium-dependent potentiation in subfield CA3 evoked by paired-pulse stimulation of mossy fibers; excitatory effects (namely an increase in spike amplitude and appearance of multiple population spikes) were seen at higher zinc concentrations. The depressant effects of an enkephalin analog on cortical firing rate were also blocked by zinc, consistent with studies from another laboratory suggesting enkephalin/zinc interactions. In contrast, the depressant effect of GABA could not be blocked by zinc, although an antagonism has been reported in the lobster muscle. Firm conclusions regarding the mechanism(s) underlying the triggering of seizure activity by zinc cannot yet be drawn, but the results of these studies would be consistent with an interference with calcium and/or potassium ion activity rather than with GABA binding sites.

Cutaneous tissue repair: practical implications of current knowledge. II

This article reviews the scientific basis for the certain factors that delay wound repair in the clinical setting. A brief history of wound healing is given, followed by a discussion of endogenous local factors (bacterial infection, hypoxia, foreign body, and desiccation) and endogenous systemic factors (nutritional deficiencies, aging, coagulation disorders, and the Ehlers-Danlos syndromes) associated with poor wound repair. Also reviewed are the mechanisms by which exogenously administered agents (glucocorticoids, antineoplastic agents, and anticoagulants) may delay healing. Commonly used topical antimicrobials, their spectrum of activity, and evidence of effects on wound healing are examined. Finally, properties of commercially available wound coverings and wound care in the future are discussed.

The effect of chelating agents on the elemental composition of sarcoplasmic reticulum: the reactivity of SH groups with N-(1-pyrene)maleimide

Treatment of sarcoplasmic reticulum vesicles with ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA), Chelex-100, 1,10-phenanthroline, 8-hydroxyquinoline, or 8-hydroxyquinoline sulfonic acid increases the reactivity of SH groups with N-(1-pyrene)maleimide (PMI). The effect of Chelex treatment can be reversed by the addition of 10(-6)-10(-5) M Zn2+ to the Chelex-treated microsomes. The activation of the PMI reaction by EGTA was not reversed by subsequent addition of calcium, although the presence of excess calcium during EGTA treatment abolished the effect. Analysis of the elemental composition of sarcoplasmic reticulum by plasma emission spectroscopy indicates the presence of Zn, Cu, Fe, and Hg in amounts of 1-2 nmol/mg protein; of these only the Zn content is reduced significantly by treatment of microsomes with EGTA or Chelex-100. These observations suggest that Zn2+ may play a role in the regulation of the reactivity of SH groups in sarcoplasmic reticulum either by direct interaction with cysteinyl residues or by an effect upon the conformation of a subpopulation of ATPase molecules.

Zinc in the seminal vesicle and cranial and caudal prostate of rhesus monkey (Macaca mulatta): testicular regulation and subcellular distribution

Zinc concentration and its subcellular distribution in the seminal vesicle and cranial and caudal prostate of adult rhesus monkey was determined by atomic absorption spectroscopy. Its concentration (microgram/mg protein) was maximum in the caudal lobe of prostate (5.7 micrograms) followed by cranial prostate (2.8 micrograms) and seminal vesicle (1.26 microgram). Analysis of subcellular fractions revealed that zinc concentration was highest in the microsomal fraction constituting about 50% of total zinc in the two lobes of prostate (cranial: 5 micrograms; caudal: 17 micrograms/mg protein). A significant reduction occurred in their zinc content following castration. The possible role of zinc in the accessory sex glands is discussed.

Effect of zinc supplementation on hyperprolactinaemia in uraemic men

Zinc and prolactin levels were measured in 32 male haemodialysis patients; 12 were receiving 50 mg zinc per day as zinc acetate and 20 were not. Zinc-treated patients had significantly higher plasma zinc levels (134 +/- 10 micrograms/dl v 88 +/- 2 micrograms/dl) and lower serum prolactin levels (11 +/- 4 ng/ml v 29 +/- 7 ng/ml) than untreated patients. Plasma zinc and serum prolactin were inversely related in zinc-treated and untreated patients (r = -0.79, p less than 0.001).

Association between urinary zinc excretion and lymphocyte dysfunction in patients with lung cancer

Patients with bronchogenic carcinoma often have low serum zinc concentrations and sometimes have markedly elevated renal zinc losses. Since normal zinc metabolism is critical for the proper function of T lymphocytes and natural killer cells, the effect of zinc status on T cell phytohemagglutinin response and peripheral blood lymphocyte natural killer cell activity was studied in patients with lung cancer. Mean (+/- SEM) serum zinc concentration in 75 patients with cancer was 67.4 +/- 2.2 micrograms/dl versus 96.0 +/- 8.0 micrograms/dl for normal subjects. Patients with low serum zinc levels (less than 70 micrograms/dl) had significantly higher urine zinc excretion than patients with normal serum zinc levels (1,385 +/- 240 micrograms per 24 hours versus 392 +/- 107 micrograms per 24 hours) (p less than 0.001). This pattern of zinc concentrations (i.e., low serum zinc in combination with high urine zinc) is typical of patients with mild zinc deficiency, and suggests that a mild chronic zinc deficiency state was present in some of these patients. When lymphocyte data were analyzed according to serum zinc concentrations and urinary zinc excretion, low serum zinc concentration and high urine zinc excretion both correlated with depressed T cell phytohemagglutinin response (p less than 0.005 and p less than 0.001, respectively). For instance, mean maximal phytohemagglutinin response in patients with urinary zinc excretion of more than 700 micrograms per 24 hours was 22,132 +/- 3,201 cpm (n = 14) compared with 68,130 +/- 6,850 cpm for patients with normal zinc excretion (n = 7). Peripheral blood lymphocyte natural killer cell activity did not correlate with either serum or urine zinc values. Oral zinc sulfate (220 mg, three times daily for six weeks) was then administered to patients with hyperzincuria (mean = 992 micrograms per 24 hours). Zinc-supplemented patients had normalization of T cell phytohemagglutinin response after zinc therapy, whereas control patients demonstrated continued T cell dysfunction. Natural killer cell activity did not change in either group during the study period. These data suggest that a mild subclinical zinc deficiency state may exist in some patients with lung cancer and may be an important cause of abnormal T cell function. Furthermore, zinc supplementation may be useful to improve lymphocyte function in selected patients. Whether zinc supplementation would alter the course of the disease or the patient's prognosis is presently unknown.

Physiology and metabolism of essential trace elements: an outline

Man depends on at least nine trace elements--iron, zinc, copper, manganese, iodine, chromium, selenium, molybdenum and cobalt--for optimum metabolic function. These elements serve a variety of functions including catalytic, structural and regulatory activities in which they interact with macromolecules such as enzymes, pro-hormones, pre-secretory granules and biological membranes. These micronutrients are involved, therefore, in all major metabolic pathways at levels which are so fundamental that the features of deficiency of many of them are protean and non-specific. In considering the metabolism of the elements themselves, they fall into two groups: those which exist normally as cations and those present as anions. The latter group are absorbed relatively easily and whole-body homeostasis is mediated mainly by renal excretion. The cations need specific pathways for absorption and their homeostasis is effected by gastrointestinal and biliary secretion. Some elements are absorbed more efficiently as organic complexes. The net achievement of the metabolic pathways for each element is to deliver it to its functional site(s) by exploiting its physicochemical characteristics to avoid interactions with other inorganic nutrients.

Zinc, cadmium, metallothionein, and progesterone: do they participate in the etiology of pregnancy induced hypertension?

Cadmium, a toxic heavy metal, has been incriminated in the etiology of essential hypertension. Zinc, an essential micronutrient necessary for growth, competes with cadmium for binding sites in biochemical processes; zinc deficiency states (i.e. pregnancy and low protein diet) might expose an individual to increased risk of cadmium toxicity. The increased sensitivity to cadmium during pregnancy could also be related to the effect of progesterone on zinc and cadmium metabolism through the actions of metallothionein (MT). MT is a low molecular weight protein believed to function in cadmium detoxification. Several studies in lab animals have documented a late gestation drop of maternal MT levels. This was thought to be due to rising progesterone levels. If there is also a late gestation drop in human maternal MT, then the propensity toward maternal cadmium toxicity would be enhanced. Therefore, we propose that when a zinc deficient woman becomes pregnant and is exposed to both the nutritional demands of the fetus and to the influence of progesterone, she will be likely to develop the manifestations of cadmium toxicity (i.e. hypertension, proteinuria, edema, etc.).

Intravesicular localization of zinc in rat telencephalic boutons. A histochemical study

A transition metal (presumably zinc) has been localized inside the synaptic vesicles of rat telencephalic boutons which make asymmetric synaptic contacts (Gray type I). A modification of Timm's sulphide-silver method for electron microscopy was applied to different areas of the rat forebrain: olfactory bulb, septum, caudate-putamen, amygdaloid complex, neocortex, entorhinal cortex and different parts of the hippocampal formation, viz. subiculum, stratum radiatum and oriens of both regio superior (CA1) and regio inferior hippocampi (CA3), the mossy fibre zone and the hilus fascia dentata and stratum moleculare in the gyrus dentatus. It was observed that the Timm staining in all these areas was located in synaptic boutons. Labelled boutons displayed a population of round clear vesicles and few dense core vesicles and made asymmetric synaptic contacts on dendritic spines. Silver granules in these boutons were confined to only a minor fraction of the round clear vesicles (approximately 10%). Labelled boutons occasionally showed silver granules in the synaptic clefts. The possible involvement of vesicular zinc in synaptic transmission is discussed.

Reduced zinc in peripheral blood cells from patients with inflammatory connective tissue diseases

By the use of the nuclear microprobe technique, the concentrations of zinc in isolated erythrocytes, platelets, and granulocytes were measured in patients with rheumatoid arthritis, other inflammatory arthritides, and scleroderma. Markedly reduced cellular zinc values were found compared to those measured in healthy subjects. No relation was found to inflammatory activity or disease duration. Plasma zinc was reduced in the majority of the patients and was negatively correlated to the inflammatory activity estimated by ESR and serum orosomucoid. No relation was found between total zinc values in plasma or cells or disease duration. Corticosteroid therapy was instituted in a number of the patients with inflammatory arthritides and induced a significant elevation of total zinc in all cell types, although normalization was not achieved. Plasma zinc values remained unchanged during the treatment.

Fusion of phospholipid vesicles induced by Zn2+, Cd2+, and Hg2+

The capacity of Zn2+, Cd2+, or Hg2+ to induce fusion of phospholipid vesicles composed of 50%/50%, 60%/40%, or 80%/20% dipalmitoyl phosphatidylcholine (DPPC)/bovine brain phosphatidylserine (PS) was investigated and compared to that of Ca2+ and Mg2+. In vesicles composed of 50%/50% or 60%/40% DPPC/PS, Zn2+ and Cd2+-induced fusion at concentrations considerably lower than were required for Ca2+-induced fusion. Only limited fusion of 80%/20% DPPC/PS vesicles occurred and Zn2+ was more effective than Ca2+ or Cd2+ in inducing fusion of these vesicles. Mg2+ and Hg2+ did not induce fusion in any of the vesicle systems.

Zinc deficiency and the developing embryo

The effect ofin utero zinc deficiency on fetal development in rats is reviewed. Attention is paid to the primary biochemical lesion associated with zinc-related teratogenesis and special consideration is given to the central nervous system. Evidence is presented that the thymidine kinase salvage pathway, used for the synthesis of thymidine monophosphate in DNA synthesis, is depressed more in fetal brain tissue than in the liver. In addition, greater reliance appears to be placed on this pathway than onde novo synthesis in the fetal brain than in other tissues. Some consideration is given to the use of in vitro embryo culture in studies relating to neurogenesis, but evidence is presented of a greater capacity of explanted rat embryos to obtain zinc from maternal serum than occurs in vivo.The rapid onset of a teratogenic zinc deficiency following dietary zinc restriction is again highlighted and further studies are described which demonstrate the critical impact of a single feeding cycle, of 4 d duration, on maternal plasma zinc levels and on the extent and nature of the observed fetal abnormalities. Evidence is presented that by shifting the timing of the high dietary intake/low plasma zinc peak to coincide with a particular 48 h period between days 6 and 10 of pregnancy, the pattern of malformations thus obtained reflected the coincidence of the high dietary intake of zinc-deficient diet and the critical time of morphogenesis of several organ systems.Whereas diminished plasma zinc levels at term in zinc-deficient animals are generally well correlated with reduced growth and dysmorphogenesis of the offspring, the same is not always found in human studies. In some cases, elevated plasma zinc levels at parturition are found in mothers with growth-retarded children, or vice versa. Experimental studies with rats are reported that suggest that maternal zinc status at term may be higher in dams bearing pups stunted by exposure to a transient zinc deficiency early in pregnancy, which in turn may have reduced the demand for maternal zinc in the later stages of gestation.The protective effect of zinc on cadmium-induced teratogenesis is discussed, particularly in relation to findings concerning an interaction of these metals in the embryonic yolk sac and thus on preplacental embryonic nutrition. Possible interactions between alcohol and zinc deficiency are also considered and data are presented pointing to increased fetotoxicity and teratogenesis in the presence of both treatments and to a more specific interaction with respect to reduced cell numbers in the developing rat hippocampus. Malondialdehyde levels, which reflect the extent of lipid peroxidation in tissue, are reported to be substantially higher in microsomes from fetal rat livers whenin utero deficiency and gestational alcoholism are combined. The suggestion is made that alcohol and zinc deficiency act independently in the body, but overlap to some extent at the common biochemical locus of membrane lipid peroxidation.

The distribution of zinc in the subcellular fractions of the rhesus monkey testis

The zinc content in the testis of sexually immature, adult, and efferent duct-ligated adult rhesus monkeys was determined by atomic absorption spectrophotometry. Zinc content (μg/g wet wt) was found to be high in adult testis (165.9) when compared to immature (68.9) or efferent duct-ligated (104.2) animals. Analysis of subcellular fractions revealed that the concentration of zinc (expressed in relation to protein) was maximum in the microsomal fraction. The possible significance of this trace metal as a constituent of membrane proteins and enzymes, and as an activator of mitochondrial function in testis, is discussed.

Inhibitory effect of zinc(II) on free radical lipid peroxidation in erythrocyte membranes

New evidence in support of zinc's role as a membrane antioxidant is presented. Human erythrocyte membranes in buffered saline underwent catalase- and superoxide dismutase-inhibitable lipid peroxidation when incubated with xanthine, xanthine oxidase, and Fe(III). Free radical mediated peroxidation was measured in terms of thiobarbituric acid reactivity and iodometric determination of lipid hydroperoxides. Whereas Ca(II) had relatively little effect on lipid peroxidation, Zn(II) strongly inhibited the reaction and suppressed peroxidation-dependent lysis of resealed membranes. Inhibition of lipid peroxidation was essentially complete in the presence of 0.1 mM Zn(II), a concentration equivalent to that of added Fe(III). By contrast, Zn(II) had no effect on rose bengal-photosensitized lipid peroxidation, a predominantly nonradical, singlet oxygen-driven process. Zinc(II) also interfered with xanthine/xanthine oxidase/iron-induced peroxidation of Triton X-100-dispersed membranes, but had no effect if EDTA was present. Trivial reasons for inhibition, for example, inactivation of xanthine oxidase or complex formation with O2-, were ruled out by showing that the rate of reduction of cytochrome c by xanthine/xanthine oxidase is not affected by Zn(II). We speculate that Zn(II) acts by interfering with the redox cycling of iron, possibly by competing with the latter for membrane binding sites.

Zinc: effect and interaction with other cations in the cortex of the rat

Zinc and other cations were iontophoretically applied to neurones in the frontoparietal cortex of urethane-anaesthetised rats and their effect on the activity of these cells was examined. Slow and often prolonged increases in firing rate occurred in 45.2% of neurones after zinc application and 72.7% after barium. Calcium caused short duration decreases in firing rate in 89.3% of neurones as did manganese (78.6%) cerium (21.9%) and magnesium (33.3%). When applied simultaneously zinc blocked the depressant effect of calcium (in 79.3% of neurones) but not that of manganese or GABA; other ions were ineffective. These results suggest that zinc, which is known to be present in nerve terminals, may modulate neuronal activity.

Effects of ZnCl2 on membrane interactions in myelin of normal and shiverer mice

X-ray diffraction was used to record the effects of metal cations on the structure of peripheral nerve myelin. Acidic saline (pH 5.0) either with or without added metal cations caused myelin to swell by 10-20 A from its native period of 178 A. The X-ray patterns usually showed broad reflections, and higher orders were either weak or unobserved. With added ZnCl2, however, the swollen myelin gave diffraction patterns that retained sharp reflections to approx. 15 A spacing. Alkaline saline (pH 9.7) containing ZnCl2 produced a reduction of the myelin period by approx. 5 A which was at least twice as much as that produced by other metals. To examine the underlying chemical basis for these unique interactions of Zn2+ with myelin, we carried out parallel X-ray experiments on sciatic nerve from the shiverer mutant mouse, which lacks the major myelin basic proteins. Shiverer myelin responded like normal myelin to ZnCl2 in acidic saline; however, in alkaline saline shiverer myelin showed broadened X-ray reflections which indicated disordering of the regularity of the membrane arrays, and additional reflections were recorded which indicated lipid phase separation. This breakdown may come about by the binding of Zn2+ to negatively-charged lipids which could be more exposed due to the absence of myelin basic proteins. Electron density profiles were calculated on the assumption that, except for changes in their packing, the myelin membranes were minimally altered in structure. For both normal and shiverer myelins, treatments under acidic conditions resulted in swelling at the extracellular apposition and a slight narrowing of the cytoplasmic space. This swelling is likely due to adsorption of protons and divalent cations. Interaction between Zn2+ and myelin P0 glycoprotein could preserve an ordered arrangement of the apposed membrane surfaces. Alkaline saline containing ZnCl2 produced compaction at the cytoplasmic apposition in both normal and shiverer myelins possibly through interactions with a portion of P0 glycoprotein which extends into the cytoplasmic space between membranes.

Effect of zinc deficiency on the biosynthesis of phosphatidylcholine in rat microsomes

Phosphatidylcholine is the major lipid of all cellular membranes. Phosphatidylcholine biosynthesis in microsomes involves two enzyme pathways, choline phosphotransferase and phosphatidyl-ethanolamine methyltransferase. The present study was designed to examine the effect of zinc deficiency on these two enzymes. Male, weanling Long-Evans rats were fed a biotin-enriched 20% egg white diet deficient in zinc for 15-45 d. The specific activity (pmol phosphatidylcholine formed/min/mg microsomal protein) of choline phosphotransferase, phsophatidylethanolamine methyltransferase, and phos-phatidyldimethylethanolamine methyltransferase was determined. The latter assay measures the third methylation of phosphatidyl-ethanolamine to phosphatidylcholine. Zinc deficiency resulted in a significant increase over controls in the specific activity of phospha-tidylethanolamine methyltransferase and phosphatidyldimethyl-ethanolamine methyltransferase in liver and spleen microsomes. A significant increase in the picomoles of phosphatidylcholine formed by the choline phosphotransferase pathway occurred in liver microsomes of zinc-deficient animals. In the brain microsomes a significant decrease in specific activity of phosphatidylethanolamine methyltransferase, phosphatidyldimethylethanolamine methyltransferase, and choline phosphotransferase occurred among zinc-deficient ani-mals. These data suggest that zinc deficiency alters the biosynthesis of phosphatidylcholine, the major lipid of cellular membranes.

Zinc deficiency and anorexia in rats: the effect of central administration of norepinephrine, muscimol and bromerogocryptine

Anorexia is a major manifestation of zinc deficiency, but the mechanism(s) for this anorexia are not well defined. In this study we investigated the effects of three modulators of feeding response on the food consumption of zinc deficient rats. Zinc deficient rats showed partial resistance to norepinephrine, eating significantly less at the 20 micrograms dose than the zinc sufficient ad lib controls, and food ingestion could not be induced at the 10 micrograms dose. Similarly, higher doses of the GABA agonist, muscimol, were required to induce feeding in the zinc deficient animals compared to the zinc sufficient controls. The dopamine agonist, bromergocryptine, failed to induce feeding in the zinc deficient animals. These findings are compatible with the concept that zinc deficiency produces a generalized decrease in receptor responsibility, possibly secondary to alterations in membrane fluidity.

Zinc acutely, selectively and reversibly inhibits pituitary prolactin secretion

Perifusion of dispersed female rat pituitary cells with medium containing 50 microM zinc acetate caused an acute, sustained and rapidly reversible inhibition of prolactin (Prl) secretion. This treatment had no influence on basal release of thyrotropin stimulating hormone (TSH), luteinizing hormone (LH) or growth hormone (GH). 50 microM Zn2+ also reversibly inhibited prolactin secretion stimulated by either 50 mM K+ or 10 nM TRH, but the secretion of GH, TSH and LH which was stimulated by 50 mM K+ or stimulation of TSH by 10 nM TRH was not inhibited. Thus zinc acts in a dynamic manner to selectively influence pituitary prolactin secretion.

The effect of zinc on the ultrastructure of the trunk muscle of the larva of Clupea harengus L

The ultrastructural changes in the trunk muscle tissue of Clupea harengus L. larvae, hatched from eggs exposed to four different concentrations of zinc (0.5, 2.0, 6.0 and 12.0 ppm), were examined by morphometric analysis. The surface-to-volume ratio of the mitochondrial cristae was significantly reduced with increasing zinc concentrations. At concentrations of 2.0, 6.0 and 12.0 ppm zinc, the relative volumes of the mitochondria increased significantly and individual mitochondria were swollen. At concentrations 2.0, 6.0 and 12.0 ppm zinc, the relative volumes of the myofibrils decreased significantly. At concentrations of 6.0 and 12.0 ppm zinc the sarcoplasmic reticulum showed significant swelling, and in specimens treated in 12.0 ppm zinc the sarcoplasm contains fewer ribosomes.

Leukocyte zinc in the assessment of zinc status

The problems of assessment of human zinc status are reviewed, with particular emphasis on the limitations to each of the current available measurements. The advantages and limitations of leukocytes are then described. Methods of preparation and potential problems in the assay for zinc are described in detail. The data so-far produced by this method are reviewed.

Zinc content in the epididymis, vas deferens, prostate, and seminal vesicles of juvenile rhesus monkey (Macaca mulatta): effect of androgen and estrogen

The zinc content in the three segments of the epididymis (caput, corpus, and cauda), vas deferens, seminal vesicles, and prostate of juvenile monkeys was determined by atomic absorption spectrophotometry. Zinc content (micrograms/gm wet weight) was found to be maximum (328) in the vas deferens; in the other organs it measured in the following order: caput 191, corpus 238, cauda 193, prostate 133 and seminal vesicles 85. In order to investigate the endocrine control of the zinc in these organs, two groups of animals were treated with testosterone propionate (2 mg) or estradiol dipropionate (10 micrograms) once daily for 30 days. In response to androgen, a rise in both concentration and content of zinc was evident only in the prostate. The results further suggested that the prostatic zinc may be under dual hormonal control, but in the epididymis and vas deferens it may be under the influence of estrogen. It is concluded that the hormonal effects on zinc content and growth stimulation in accessory sex organs are quite separate and may be under different hormonal control.

Interactions between trace elements and alcohol in rats

Interactions between ethanol and trace elements are reviewed at two levels. The first concerns the effect of alcohol on the concentration and distribution of certain trace metals in the body; changes are described for copper, iron, manganese, selenium and zinc. The second relates to the possible protection afforded by some trace elements against alcohol-related damage. The significance of maternal zinc to the fetal alcohol syndrome is discussed in the light of evidence that pregnancy outcome in rats after gestational alcoholism is less favourable in zinc-deficient dams than in nutritionally replete animals. Cellular metabolism of ethanol may lead to the generation of damaging superoxide and hydroxyl radicals; several trace elements, notably zinc, manganese, selenium and copper, may function protectively as free radical scavengers and as antioxidants. Evidence is presented of increased lipid peroxidation in zinc-deficient tissues of Sprague-Dawley rats and of enhanced activity of Mn-superoxide dismutase in fetal and adults rats exposed to ethanol.

The movement of zinc and copper from the fertilized egg into metallothionein-like proteins in developing chick hepatic tissue

The movement of copper and zinc from the fertilized egg into the developing embryo and the subsequent association of the two metals with metallothionein-like proteins (MT) of chick liver was investigated. Hepatic levels of MT in 1-d-old chicks, estimated from specifically bound(115m)Cd, were increased eightfold over endogenous levels of these copper- and zinc-binding proteins in adult liver. Copper was assimilated from the oocyte into the embryo more rapidly than zinc in the early stages of embryogenesis. Between 15 and 16 d of development, during the time that (MT) was detected, there was a significant increase in copper concentration, whereas hepatic zinc concentration remained relatively constant.

Pre- and postsynaptic effects of zinc on in vitro prepyriform neurones

Intracellular recordings from guinea-pig olfactory cortex neurones revealed a dual effect of zinc: firstly (at 100-500 microM), the responses to bath-applied GABA, muscimol and 3-aminopropanesulphonate were reversibly enhanced, and secondly (at 25-500 microM), the excitatory postsynaptic potential was dramatically prolonged. At Zn2+ doses higher than 50 microM, transmission was eventually blocked irreversibly. These effects of zinc were not produced by 4-aminopyridine, or other divalent cations. The GABA-enhancement is suggested to occur via an interaction of Zn2+ with the post-synaptic GABA receptor, and the prolonged transmitter release probably via blockade of an outward current in nerve terminals. The latter effect may be a contributory factor in the epileptogenic activity of zinc.

Zinc localization in taste bud membranes

Zinc was measured by flame aspiration atomic absorption spectrophotometry in homogenates and in enriched fractions and subfractions from bovine taste bud membranes and from surrounding control tissues that contained no taste buds. Zinc was found in significantly higher concentrations in tissues containing taste buds and increased in concentration as biochemical and electron microscopic purity increased. The role of zinc in taste bud membranes could relate to its role in membrane stabilization or to its activity in alkaline phosphatase, a zinc-dependent enzyme whose specific activity increased in taste bud membranes in the same manner as did zinc concentration.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.

A novel effect of zinc on the lobster muscle GABA receptor

The effect of zinc (and copper) was investigated on the lobster muscle gamma-aminobutyric acid (GABA) receptor. Zinc (10 microns-1 mM) depressed the GABA-evoked conductance increase in a fully reversible manner by possibly binding to an imidazole group, suggested from pH titration studies on the evoked-chloride conductance. Other transition metal (period 4) divalent cations (up to 500 microM) were inactive in antagonizing GABA responses. Variation of external chloride or anion substitution did not perturb the zinc antagonism; however, decreasing the pH markedly decreased the potency of zinc. A possible explanation for these results is discussed. Although the zinc antagonism resembled that produced by picrotoxinin, combination of these two agents depressed the GABA dose--conductance curve in a manner expected for two antagonists acting on independent sites. The zinc binding site was also discrete from the GABA recognition site; the results are interpreted in terms of a distinct binding site for zinc and H+. The distortion of an agonist dose--response curve by formation of an inactive agonist-divalent cation complex is discussed; however, complexation of GABA did not explain the observed antagonism by zinc. By comparison, zinc had no effect on the GABA responses of rat ganglionic neurons. It is concluded that the zinc binding site, on lobster muscle, may be an important modulatory site for the GABA-evoked chloride conductance.

Foetal mortality in moderately zinc-deficient rats is strictly related to the process of parturition: effect of maternal essential fatty acid supplementation

1. Although disrupted parturition and high foetal losses have previously been reported in pregnant rats maintained on zinc-deficient diets this is the first report to differentiate between the effects of reduced Zn intake and the effects of reduced food intake on the outcome of pregnancy in the rat. 2. Rats maintained on a 0.5 mg Zn/kg diet for the last 7 d of gestation or on a 5 mg Zn/kg diet throughout gestation did not consume significantly less food than rats given 10 or 20 mg Zn/kg diets except during the last 2d of gestation. Pair-feeding of Zn-adequate rats (20 mg/kg) to those given low-Zn diets for the last 2 d of gestation did not affect the outcome of pregnancy in these rats. 3. In the rats maintained throughout gestation on 5 mg Zn/kg or on 0.5 mg Zn/kg in the last 7 d of gestation, parturition onset and duration were not significantly altered. Foetal survival was very significantly reduced but only from day 22 onwards; before the onset of parturition, foetal survival was not significantly affected by Zn deficiency during gestation. 4. Subcutaneous injection of evening primrose (Oenothera biennis) oil into rats throughout gestation enhanced foetal and neonatal survival in rats given 5 mg Zn/kg but reduced foetal survival in rats given 0.5 mg Zn/kg in the last 7 d of gestation. 5. The results suggest three points: (1) subtotal Zn deficiency during gestation in the rat jeopardises foetal survival at parturition without affecting the onset or duration of parturition, (2) foetal death in rats maintained on Zn-deficient diets occurs only in relation to parturition itself, (3) provided that Zn intake near term is at least 5 mg/kg, supplemental essential fatty acids (evening primrose oil) will reduce foetal mortality during parturition and in the neonatal period.

Degeneration and regeneration of olfactory cells induced by ZnSO4 and other chemicals

The necrotic effect of various salt solutions was tested on the catfish olfactory mucosa. Only zinc cations were able to induce an extensive degeneration of the olfactory cells. Two different modes of irrigation of the mucosa with zinc sulfate were investigated. (1) The olfactory cavity is flushed with the chemical for not more than a few seconds. At concentrations above 30 mM, the resulting damage is very reproducible, largely concentration independent and almost completely specific for the olfactory receptor cells. The non-sensory respiratory cells are unaffected, the sustentacular cells surrounding the receptor cells are affected mainly by a loss of microvilli. The olfactory receptor cells, on the contrary, start to degenerate within a few hours and by day 4 only 20% of the original receptor population remains. Division of the mucosal basal cells increases during days 3 and 4 on and day 6 olfactory receptor cells reach the bare surface of the lamella. After day 7, the receptor population reaches a level of more than 80% of its original value. Because of the absence of sustentacular processes covering the olfactory cell's knobs on day 6, it has been possible to confirm that each of the two types of olfactory receptor cells previously characterized are concentrated on each half of the mucosa (2) The salt is maintained in contact with the tissue for several days. After this treatment most of the lamellae are irreversibly destroyed, some regeneration occurs in limited areas of the mucosa. In these small areas, indifferent respiratory cells reappear first between 20 and 35 days. It is only when the structure of the olfactory tissue is completely reorganized that the new receptor cells reappear between days 45 and 55. Regeneration is not completed before 60-65 days.

Zinc deficiency-induced trace element concentration and localization changes in the central nervous system of albino rat during postnatal development. II. Atomic absorption spectrophotometric examinations

The changes in the zinc and copper concentrations in the central nervous system (spinal cord, cerebellum, cerebrum, hippocampus, corpus striatum) of albino rat were studied by atomic absorption spectrophotometry in a state of zinc deficiency induced experimentally during the first 30 days of postnatal ontogenesis. It was found that in these structures the zinc deficiency is able to influence the changes and tendencies in the trace element content essentially only in an area undergoing intensive development in the given period, or which is sensitive to unsatisfactory dietary influences. The results lead to the assumption that the state of zinc deficiency is accompanied by a change in the distribution of the trace element content within the cells.