Maternal zinc deficiency impairs brain nestin expression in prenatal and postnatal mice

INTRODUCTIONZinc is essential for normal brain development,evidenced by the fact that zinc deficiency in lactating mothers is characterized by a high incidence ofneuroanatomical maiformatinns and functional abnormalities in suckling offspring[1-3]. By colltrast,relatively little is known about the relationship be{tween maternal zinc nutrition and fetal brain development[2, 4, 5]. Dvergsten et al[6-81 investigated theeffects of maternal zinc deficiency on postnatal development of the rat ce…     

Calcium exacerbates the inhibitory effects of phytic acid on zinc bioavailability in rats

BackgroundComplementary feeding of breastfed infants with foods high in bioavailable zinc (Zn) can help meet physiological requirements for Zn. Some infant cereals contain high concentrations of phytic acid (PA) and calcium (Ca) that may reduce absorbable Zn.ObjectivesThis study measured PA, Zn and Ca concentrations in selected infant cereals sold in Canada and investigated the effects of dietary PA and Ca at concentrations present in infant cereals on Zn bioavailability in rats.Methods and resultsMale Sprague-Dawley rats (36-day old) were fed a control diet containing normal Zn (29.1 mg/kg) and Ca (4.95 g/kg) or six test diets (n = 12/diet group). Test diets were low in Zn (8.91–9.74 mg/kg) and contained low (2.16–2.17 g/kg), normal (5.00–5.11 g/kg) or high (14.6–14.9 g/kg) Ca without or with added PA (8 g/kg). After 2 weeks, rats were killed and Zn status of the rats was assessed. PA, Zn and Ca concentrations in infant cereals (n = 20) differed widely. PA concentrations ranged from undetectable to 16.0 g/kg. Zn and Ca concentrations ranged from 7.0–29.1 mg/kg and 0.8–13.4 g/kg, respectively. The [PA]/[Zn] and [PA × Ca]/[Zn] molar ratios in infants cereals with detectable PA (16 of 20 cereals) ranged from 22–75 and 0.9–14.9 mol/kg, respectively, predicting low Zn bioavailability. Body weight, body composition (lean and fat mass), right femur weight and length measurements and Zn concentrations in serum and femur indicated that diets higher in Ca had a more pronounced negative effect on Zn status of rats fed a PA-supplemented diet. Addition of PA to the diet had a greater negative effect on Zn status when Ca concentration in the diet was higher.ConclusionThese results show that, in rats, higher concentrations of dietary Ca and PA interact to potentiate a decrease in bioavailable Zn and may suggest lower Zn bioavailability in infant cereals with higher PA and Ca concentrations.     

Usefulness of the dietary phytic acid/ zinc molar ratio as an index of zinc bioavailability to rats and humans

Evidence suggests that rats can tolerate a dietary phytate/Zn molar ratio greater than 15 if the dietary Zn concentration is high. High dietary Ca exacerbates the effect of phytic acid on Zn utilization by rats. In a short term (15 d) balance trial with adult men, we observed slightly greater Zn balance when whole compared to dephytinized wheat bran was consumed (molar ratios 12 and 1.2, respectively). There was, however, greater fecal excretion of Zn during the first 5 d whole bran was consumed. In a second study, Na phytate was the major source of phytic acid and Zn balance was less when the phytate/Zn molar ratio was greater than 16 compared to 4. The difference was not significant, however, and there was evidence of physiological adjustments to maintain homeostasis when the high ratio diet was consumed. Mean Zn intake averaged 17 mg (0.26 mmole) and 11 mg (0.17 mmole) daily for the bran and Na phytate studies, respectively. The level of Zn intake may influence the response of humans to varying phytate/Zn ratios. Comparison of isotope retention studies and the balance data is discussed. Some information on the relationship of dietary Ca to the phytate/Zn effect in human diets is gathered from current literature. The phytate/Zn molar ratio is a useful index of Zn bioavailability.     

Variation in elemental intensities among teeth and between pre- and postnatal regions of enamel

Microspatial analyses of the trace element composition of dental enamel are made possible using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Fine spatial resolution, multielement capabilities, and minimal sample destruction make this technique particularly well-suited for documenting the distribution of elements in sequentially calcifying layers of enamel. Because deciduous enamel forms from week 13 in utero up to 9 months postnatally (thereafter essentially becoming inert), the application of LA-ICP-MS allows for the retrospective measurement of prenatal and early postnatal trace-element uptake during a critical period of child development. In this study, we compared intra- and intertooth intensities of 25Mg, 57Fe, 66Zn, 68Zn, 88Sr, 138Ba, and 208Pb via LA-ICP-MS of 38 exfoliated deciduous incisors and canines donated by 36 participants in the Solís Valley Mexico Nutrition Collaborative Research Support Program (NCRSP). Pre- and postnatal comparisons within teeth showed significant increases (P < 0.001) and greater variation in the abundance of all isotopes in postnatal enamel, with the exception of a decrease in 25Mg (P < 0.001) and constant values for 88Sr (P = 0.681). Conversely, comparisons by tooth type and mouth quadrant revealed few significant differences between teeth of the same individual. We argue that more variation in the trace element composition of teeth occurs across developmental areas within a tooth than among different teeth of the same person. This study further demonstrates that sequentially calcifying areas of enamel have different chemical concentrations. The results support the use of microspatial analyses of enamel for understanding changes in nutrition, pollution, and residence.     

Pre- and Post-Natal Maternal Depressive Symptoms in Relation with Infant Frontal Function,Connectivity, and Behaviors

This study investigated the relationships between pre- and early post-natal maternal depression and their changes with frontal electroencephalogram (EEG) activity and functional connectivity in 6- and 18-month olds, as well as externalizing and internalizing behaviors in 24-month olds (n = 258). Neither prenatal nor postnatal maternal depressive symptoms independently predicted neither the frontal EEG activity nor functional connectivity in 6- and 18-month infants. However, increasing maternal depressive symptoms from the prenatal to postnatal period predicted greater right frontal activity and relative right frontal asymmetry amongst 6-month infants but these finding were not observed amongst 18-month infants after adjusted for post-conceptual age on the EEG visit day. Subsequently increasing maternal depressive symptoms from the prenatal to postnatal period predicted lower right frontal connectivity within 18-month infants but not among 6-month infants after controlling for post-conceptual age on the EEG visit day. These findings were observed in the full sample and the female sample but not in the male sample. Moreover, both prenatal and early postnatal maternal depressive symptoms independently predicted children’s externalizing and internalizing behaviors at 24 months of age. This suggests that the altered frontal functional connectivity in infants born to mothers whose depressive symptomatology increases in the early postnatal period compared to that during pregnancy may reflect a neural basis for the familial transmission of phenotypes associated with mood disorders, particularly in girls.     

Maternal Zinc Supplementation Improves Spatial Memory in Rat Pups

A large body of evidence supports an opinion that adequate dietary zinc is essential for prenatal and postnatal brain development. Behavioural effects of maternal supplementation with ZnSO(4) were analysed in rat pups with the Morris water task performance, a hole board and a T-maze. Wistar females during pregnancy and lactation received a drinking water solution of ZnSO(4) at doses of 16 mg/kg (group Zn16) or 32 mg/kg (group Zn32). Behavioural tests were conducted on the 4-week-old male rat pups. Zinc concentration in the serum, hippocampus and prefrontal cortex of offsprings was determined by means of atomic absorption techniques. The Newman-Keuls multiple comparison test revealed an increase of climbing in the Zn16 group in comparison to the control group (Con) and the Zn32 group during the hole board test. ANOVA for repeated measures showed a significant memory improvement in both supplemented groups compared to the control in the probe trial on day 5 of the water maze test. ZnSO(4) treatment significantly elevated zinc levels in the rat serum. Follow-up data on brain content of zinc in the hippocampus revealed significant differences between the groups and in supplemented groups correlated with crossings above the original platform position. These findings suggest that pre- and postnatal zinc supplementation may improve cognitive development in rats.     

Excess calcium increases bone zinc concentration without affecting zinc absorption in rats

We examined zinc (Zn) metabolism in rats given diets containing excess calcium (Ca). Rats were given phytate-free diet containing 5 g Ca/kg (control), 12.5 g Ca/kg, or 25 g Ca/kg for 4 wk in Experiment 1. The dietary treatment did not affect Zn concentration in the plasma, testis, kidney, spleen and liver; however, Zn concentration in the femur and its cortex was significantly higher in rats given diet containing 25 g Ca/kg than in other rats. Rats were given phytate-free diet containing 5 g Ca /kg or 25 g Ca /kg for 4 wk in Experiment 2. After 12-h food deprivation, rats were given a diet extrinsically labeled by 67Zn with dysprosium as a fecal marker for 4 h. Feces were collected from 1 d before administration of the labeled diet to 5 d after administration. Excess Ca did not affect the true absorption of Zn and its endogenous excretion but increased femoral Zn. These results suggest that excess Ca improves Zn bioavailability without affecting Zn absorption when diets do not contain phytate.     

Influence of low dietary calcium during pregnancy and lactation on zinc levels in maternal blood and bone in rats.

The effect of low dietary calcium on maternal zinc nutritional status was studied. Two groups of 6 adult female Wistar rats were fed during pregnancy and lactation with experimental diets containing either 0.2 g (LCa) or 0.6 g (NCa) of calcium/100 g. Both diets contained/100 g: 20.0 g protein (potassium caseinate), 3.5 mg Zn, 0.6 g P. A third group (n = 6) was fed a "stock diet" (SG), containing/100 g: 24.8 g protein, 1.5 g Ca, 0.6 g P, 11.6 mg Zn. Maternal blood samples were drawn from the tail before mating (To), at delivery (D) and at weaning (W); dams were sacrificed at weaning and the right femur was excised. Determinations (atomic absorption spectrometry) were: Zinc in red blood cells (RBC), Zn and Ca in ashed femur. The results (mean +/- SD) were: RBCZn (microg/mL) at To: 8.65 +/- 1.80, which did not change in the SG or in the NCa groups, but increased significantly in the LCa group (p < 0.001) (D: 18.20 +/- 4.63; W: 26.70 +/- 6.02), regarding To. Femur Zn (microg/100 mg) showed an increase (p < 0.001) in the LCa group (30.2 +/- 2.1) regarding both SG (25.3 +/- 0.7) and NCa groups (24.1 +/- 0.7). Femur Ca (mg/100 mg) decreased (p < 0.05) in the LCa group (19.2 +/- 0.9) regarding both SG (24.0 +/- 0.5) and NCa groups (21.4 +/- 0.7) and leading to a significant increase in Zn/Ca ratio (p < 0.001) in the LCa group. Therefore, dietary calcium deficiency during pregnancy and lactation would produce an increase of Zn utilization, reflected in the increase of maternal blood Zn levels and in femur Zn content.     

Zinc and manganese bioavailability from human milk and infant formula used for very low birthweight infants,evaluated in a rat pup model

The bioavailability of zinc and manganese from diets used for very low birthweight infants was investigated in a rat pup model using radioisotopes. The effect of protein source and content and of pasteurization was evaluated, and two different approaches for evaluation of zinc and manganese bioavailability in the rat pup model were compared. Zinc and manganese bioavailability from the studied human milk and infant formula for very low birthweight infants was high. Liver uptake of⁶⁵Zn from labeled premature infant diets in sucklings rat pups was 26–29%, and absorption calculated as the difference between administered dose and nonabsorbed activity 6 h after oral intubation was 93–95%. Retention of manganese calculated as the sum of⁵⁴Mn retained by organs and carcass was 85–95% from human milk and premature infant formula and absorption calculated from nonabsorbed activity was 83–88% after 6 h. Fortification of early human milk significantly increased the bioavailability of zinc. No effect of pasteurization of human milk was found on zinc or manganese bioavailability. Liver zinc uptake was found to be a more sensitive parameter than absorption for evaluation of diets with a high zinc bioavailability. Measurement of retained activity of manganese in carcass and organs was judged to be the preferred parameter for evaluation of diets with high manganese availability.     

Tracking dietary transitions in weanling baboons (Papio hamadryas anubis) using strontium/calcium ratios in enamel

Strontium and calcium are incorporated into developing teeth in a manner that reflects changing physiological concentrations in the body. A new model predicts changes in strontium/calcium (Sr/Ca) ratios in response to dietary transitions experienced at birth and during the weaning period. Microsampling of longitudinal thin sections of tooth enamel using laser ablation inductively coupled plasma mass spectrometry provides a basis for the systematic evaluation of variation in Sr/Ca ratios within the tooth crown. Incremental growth markers in enamel are used to determine the age of onset of enamel mineralization at each sampling point. Thin sections of 5 teeth from 2 wild-caught baboons (Papio hamadryas anubis) were systematically analysed using this technique. Intra- and intertooth analyses of Sr/Ca ratios reveal a pattern of dietary development during the period of enamel formation that is consistent with observational data on the timing of weaning behaviour in anubis baboons.     

Dietary zinc intake of a group of longstay mentally handicapped women some bioavailability considerations

Dietary factors affecting zinc bioavailability were evaluated according to their relative distribution in the individual daily meals making up the basic diet of 17 institutionalized, mentally handicapped adult women. Mean intake values of zinc, phytate, nonstarch polysaccharides (NSP), calcium, protein, and energy were calculated from a dietary survey of 7 consecutive days, which also served to obtain values for the two zinc bioavailability predictor formulas, phytate/Zn millimolar ratio and [Ca] [phytate]/[Zn][energy] ratio. Mean daily zinc intake was 8.5 ±1.8 mg, with noon and evening meals accounting for the highest contribution to this value (45% and 35%, respectively), whereas breakfast meals’ contribution was 16%. The mean protein intake was 55 ±13 g, with noon and evening meals being the major contributors to total daily intake (42% and 38%, respectively). Breakfast meals accounted for 77% of daily phytate intake, giving a respective phytate/Zn millimolar ratio of 20.4 ±7.6 and a [Ca][phytate]/[Zn][energy] ratio of 336 ±127 mmol/Mcal. Values for both ratios based on noon and evening meals were negligible in comparison. The mean daily NSP intake was 9.8 ±4.2 g, with 53% of total daily intake supplied from breakfast meals, whereas noon and evening meals accounted for 30% and 14%, respectively. The results, while suggesting that zinc bioavailability is unlikely to be adversely affected, indicated that dietary fiber intake levels are probably inadequate, particularly in view of the nonambulant condition and low physical activity prevalent in such individuals, who may, as a consequence, be susceptible to health disorders associated with impaired bowel function and constipation.     

Aspects of trace element interactions during development

The origins of nutritional trace element deficiencies are summarized. Inadequate intake results in primary deficiency, whereas secondary or conditioned deficiencies can arise in several ways including trace element interactions. Evidence is presented and discussed for interactions of essential trace elements during prenatal and early postnatal development. Diets of widely different zinc and copper concentrations and ratios were fed to pregnant rats. Analysis of fetal outcome and copper and zinc concentrations of maternal and fetal livers showed that although there is an interaction between these metals it occurs only at levels of dietary copper deficiency. Iron and manganese interact so that high levels of one depress absorption of the other. Mice fed iron-supplemented diets had liver manganese concentrations lower than those of unsupplemented mice. Iron supplements at high but not low levels also depressed absorption of zinc. Conversely, zinc deficiency in pregnant rats caused higher than normal concentrations of iron in maternal and fetal liver. Trace element analyses of proprietary infant formulas indicate that in some, concentrations and ratios of these trace elements may be incorrect. The effects of essential trace element interactions during development should be further investigated. Caution is urged in considering levels of trace element supplements during pregnancy, lactation, or early childhood.     

Nutritional quality of gorilla diets: consequences of age,sex, and season

We tested the effects of age, sex, and season on the nutritional strategies of a group of mountain gorillas (Gorilla beringei) in the Bwindi Impenetrable National Park, Uganda. Through observations of food intake of individual gorillas and nutritional analyses of dietary components over different seasons and environments, we estimated nutrient intake and evaluated diet adequacy. Our results suggest that the nutritional costs of reproduction and growth affect nutrient intake; growing juveniles and adult females ate more food and more protein per kilogram of metabolic body mass than did silverbacks. The diets of silverback males, adult females, and juveniles contained similar concentrations of protein, fiber, and sugar, indicating that adult females and juveniles did not select higher protein foods than silverbacks but rather consumed more dry matter to ingest more protein. Juveniles consumed more minerals (Ca, P, Mg, K, Fe, Zn, Mn, Mo) per kilogram of body mass than adult females and silverback males, and juveniles consumed diets with higher concentrations of phosphorous, iron, and zinc, indicating that the foods they ate contained higher concentrations of these minerals. Seasonally, the amount of food consumed on a dry weight basis did not vary, but with increased frugivory, dietary concentrations of protein and fiber decreased and those of water-soluble carbohydrates increased. Energy intake did not change over the year. With the exception of sodium, gorillas ate diets that exceeded human nutrient requirements. A better understanding of the relative importance of food quantity and quality for different age–sex classes provides insights into the ways in which gorillas may be limited by food resources when faced with environmental heterogeneity.     

DIETARY STUDIES OF MARINE MAMMALS USING STABLE CARBON AND NITROGEN ISOTOPIC RATIOS OF TEETH

This study used naturally occurring carbon and nitrogen stable isotopes of teeth to study the diets of marine mammals. The isotopic ratios of nonchemically preserved teeth from eight species of marine mammals, representing 87 individuals that spanned the trophic continuum, were found to reflect nutritional sources. The δ¹³C signals distinguished animals that lived in waters dominated by different primary producers (e. g., seagrass, kelp, and phytoplankton), and δ¹⁵N values indicated the diet and trophic level of the species. This research suggests that isotopic signatures of teeth can be used in dietary studies to show differences and similarities among age classes, genders, geographic locations, and time periods.     

Developmental effects and mineral interactions in rats fed textured vegetable protein

The teratogenic effects of feeding a diet based on textured vegetable protein to Long-Evans rats were studied along with maternal and fetal mineral interactions and their relationship to diet composition. Pregnant rats were fed purified diets containing 18% protein as casein (CAS), textured vegetable protein (TVP, from defatted soy flour) with 18 mg Zn/kg, or TVP diet with 100 mg Zn/kg. A fourth group was fed diet NIH-31. The animals received their diets throughout pregnancy and were sacrificed on day 20 of gestation. Fetuses were examined for developmental effects, and mineral levels were determined in maternal and fetal tissues by inductively coupled argon plasma-atomic emission spectrometry. Females fed the casein diet or diet NIH-31 had normal weight gains throughout pregnancy and their progeny exhibited normal development. The animals on the TVP-containing diet with 18 mg Zn/kg had decreased food consumption and body weights, and their fetuses exhibited developmental anomalies as well as reductions in size and weight. These developmental alterations may be the result of decreased zinc levels in the fetal tissues, caused by reduced bioavailability of the trace element in the maternal diet. Significant increases in tissue iron accompanied the low zinc levels. No developmental effects were found in animals receiving the high Zn-TVP diet, and mineral data from these animals were not significantly different from the casein group.     

Post-natal diet determines insulin resistance in fetally malnourished, low birthweight rats (F1) but diet does not modify the insulin resistance of their offspring (F2)

We examined the effects of prenatal and postnatal nutrition on birthweight and insulin sensitivity, indicated by the glucose/insulin (G/I) ratio, in adult rats (F1 generation) and in their adult offspring (F2 generation). Rat pups (F1) whose dams consumed low-protein diets during gestation (malnourished) consumed either nutritionally adequate (control) or high-fat diets ad libitum post-weaning. The offspring of these rats (F2) were maintained on the same diets as their respective dams. Separate pups (F1) whose dams consumed high-fat diets during gestation (over-nourished) were maintained on high-fat diets post-weaning, as were their offspring (F2). Birthweights were significantly reduced in all fetally malnourished F1 animals. At approximately 70 d of age, fasting insulin sensitivity in over-nourished F1 rats was significantly reduced compared to controls regardless of whether they were malnourished or over-nourished in utero; however, fetally malnourished F1 rats consuming control diets post-natally had significantly greater fasting insulin sensitivity than control animals. At 30 and 120 min post-glucose load, insulin sensitivity was reduced 12-65% in both groups of over-nourished F1 rats as compared to the fetally malnourished F1 rats consuming the control diet. Birthweights were significantly lower in F2 animals whose dams (F1) were fetally malnourished and weaned to high fat diets. Insulin sensitivity was significantly reduced in all F2 animals versus control animals, regardless of dietary treatment. Thus, post-natal diets alter insulin sensitivity in fetally malnourished, adult rats; and maternal malnutrition during gestation results in insulin resistance in offspring, irrespective of offsprings' birthweight or diet.     

Metabolic engineering of bread wheat improves grain iron concentration and bioavailability

Bread wheat (Triticum aestivum L.) is cultivated on more land than any other crop and produces a fifth of the calories consumed by humans. Wheat endosperm is rich in starch yet contains low concentrations of dietary iron (Fe) and zinc (Zn). Biofortification is a micronutrient intervention aimed at increasing the density and bioavailability of essential vitamins and minerals in staple crops; Fe biofortification of wheat has proved challenging. In this study we employed constitutive expression (CE) of the rice (Oryza sativa L.) nicotianamine synthase 2 (OsNAS2) gene in bread wheat to up‐regulate biosynthesis of two low molecular weight metal chelators – nicotianamine (NA) and 2′‐deoxymugineic acid (DMA) – that play key roles in metal transport and nutrition. The CE‐OsNAS2 plants accumulated higher concentrations of grain Fe, Zn, NA and DMA and synchrotron X‐ray fluorescence microscopy (XFM) revealed enhanced localization of Fe and Zn in endosperm and crease tissues, respectively. Iron bioavailability was increased in white flour milled from field‐grown CE‐OsNAS2 grain and positively correlated with NA and DMA concentrations.     

Beneficial effect of goat milk on bioavailability of copper, zinc and selenium in rats

We studied the effects of dietary inclusion of freeze-dried goat and cow milk on the utilization of copper, zinc and selenium, and on the metabolic fate of copper and zinc, in rats using a standard (non-milk) control diet recommended by the American Institute of Nutrition and diets based on goat or cow milk. For animals given the goat milk diet, the apparent digestibility coefficient (ADC) of copper is similar to that obtained with the standard diet and higher than that in animals given the cow milk diet. The copper balance was higher among the rats given the goat milk and the standard diets than among those given cow milk. The ADC and retention of zinc and selenium were higher for the goat milk diet than for the other two diets. The copper content in the kidneys and in the femur was greater when the animals consumed a goat milk diet than a cow milk diet. Zn deposits in femur, testes, liver, kidney, heart and longissimus dorsi muscle were greatest with the goat-milk diet, followed by the standard diet and were lowest for the rats given cow-milk diet. This study shows that the goat-milk has an important and beneficial effect on the bioavailability of copper, zinc and selenium.     

Maternal Milk Concentration of Zinc,Iron, Selenium,and Iodine and Its Relationship to Dietary Intakes

The dietary intake of zinc (Zn), iron (Fe), selenium (Se), and iodine (I) of 31 lactating Mexican–American women attending the Hidalgo County WIC program in Rio Grande Valley (RGV), Texas was estimated from 24-h dietary recall interviews. Milk samples were obtained from lactating mothers who had infants 3 months of age and younger. Milk samples were collected in two visits to assess change in breast milk composition after 1–3 months postpartum: group A—after 30–45 days and group B—75–90 days. Dietary intakes indicated that the study participants had significantly inadequate percent energy intakes than the DRI (Dietary Recommended Intakes) percent recommended kilocalorie values but protein intakes were substantially higher than the percent recommended values. The estimated percent Zn, Fe, Se, and I intakes were also significantly lower than the DRI percent recommended values. The lactating mothers consumed significantly less Zn, Se, and I when compared to the Recommended Dietary Allowances (RDA) even though Fe intake was higher than the RDA value. Breast milk concentration of Zn, Fe, and Se were in agreement within the range of representative values for Constituents of Human Milk but I has significantly less concentration than the representative value. There was no statistically significant correlation observed between dietary intake and milk concentration of Zn, Fe, Se, and I. This study compares the estimated dietary intake of zinc, iron, selenium, and iodine to the concentration of these trace elements in the maternal milk of lactating women of Mexican–American heritage who attend the Rio Grande Valley WIC clinic.     

Effects of zinc deficiency on morphogenesis of the fetal rat eye

Maternal zinc deficiency during pregnancy results in a high frequency of fetal eye malformations in the Long-Evans rat. In this study we examine the development of the eye from days 12 through 21 of gestation in conceptuses of dams fed deficient or adequate levels of zinc and also examine maternal plasma and conceptus zinc concentrations during this period. Dams were fed diets containing 0.5 (0.5 Zn group), 4.5 (4.5 Zn group), or 100 (100 Zn AL group) micrograms zinc per gram diet ad libitum, or 100 micrograms zinc g-1 diet in amounts restricted on a daily basis to the intake of matched animals from the 0.5 Zn group (100 Zn RI group). Conceptuses were removed and maternal plasma was collected on days 12, 14, 16, 19 and 21 of gestation. Maternal plasma and conceptus zinc concentrations reflected maternal dietary zinc level, with dam plasma Zn concentrations in the order of 0.5 Zn group less than 4.5 Zn group less than 100 Zn group on all days. A similar pattern held for embryo/fetus zinc, except for days 19 and 21, at which times the 0.5 Zn and 4.5 Zn fetuses had similar zinc concentrations. Histological examination of the developing eye of 0.5 Zn fetuses on days 12 and 14 revealed that invagination of the optic cup was often deficient, and that closure of the choroid fissure did not occur, resulting in colobomata and retinal folding visible at term. A very few fetuses were found at term to be anophthalmic or have only remnants of ocular tissue.(ABSTRACT TRUNCATED AT 250 WORDS)