Interspecies comparisons of A/D ratios: A/D ratios are not constant across species

The hypothesis that the ratio of the adult (A) and developmental (D) toxicity of a chemical is constant across animal species has been proposed as the basis for identifying developmental hazards, both from traditional developmental toxicity screens using laboratory mammals and from alternative systems such as the coelenterate Hydra attenuata. The purpose of this study was to determine whether A/D ratios are constant across species. The developmental and adult toxicity of 14 chemicals was assessed in four phylogenetically different species. The chemicals tested were aminopterin, bromodeoxyuridine, cadmium chloride, caffeine, congo red, dinocap, dinoseb, diphenylhydantoin, epinephrine, ethylenethiourea, 2-methoxyethanol, mirex, all-trans-retinoic acid, and trypan blue. These chemicals are representative of a variety of toxic mechanisms and a range of potencies. Species used were the CD-1 mouse (Mus musculus), South African clawed frog (Xenopus laevis), fathead minnow (Pimephales promelas), and fruit fly (Drosophila melanogaster). The mouse is a commonly used model for developmental toxicity. The other species are known to be sensitive to mammalian toxicants and have well-studied embryologies. Mice were exposed to chemicals either po or by sc injection using a standard Segment II protocol in which pregnant mice are administered the test agent on a daily basis from Gestation Days 6 to 15, adult toxicity is evaluated during and after treatment, and developmental toxicity is evaluated in fetuses at term. The exposure duration spans the period of organ formation in the embryo. The other species were exposed to test agents for a developmentally comparable period. This was from blastulation (shortly after fertilization) to the free-swimming tadpole stage in Xenopus (4 days); from blastulation to the free-swimming fry stage in Pimephales (7 days); and for the entire larval period, the period of development of the imaginal discs, in Drosophila (6 days). Adults of each species were exposed to test agents for 4, 7, and 6 days, respectively. The route of exposure was via the water column in the two aquatic species and via the diet in Drosophila. Statistical lowest observed effect level (LOEL) and no observed effect level (NOEL) values were generated for adult and developmental toxicity in each species. A/D ratios were calculated using both LOEL and NOEL values.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of metallothionein induction and altered zinc status in maternally mediated developmental toxicity: comparison of the effects of urethane and styrene in rats

We hypothesize that maternal metallothionein (MT) induction by toxic dosages of chemicals may contribute to or cause developmental toxicity by a chain of events leading to a transient but developmentally adverse decrease in Zn availability to the embryo. This hypothesis was tested by evaluating hepatic MT induction, maternal and embryonic Zn status, and developmental toxicity after exposure to urethane, a developmental toxicant, or styrene, which is not a developmental toxicant. Pregnant Sprague-Dawley rats were given 0 or 1 g/kg urethane ip, or 0 or 300 mg/kg styrene in corn oil po, on Gestation Day 11 (sperm positive = Gestation Day 0). These were maternally toxic dosages. As both treatments decreased food consumption, separate pair-fed control groups were also evaluated for effects on MT and Zn status and development. In addition, Gestation Day 11 rat embryos were exposed to urethane in vitro in order to determine whether urethane has the potential to be directly embryotoxic. Urethane treatment induced hepatic MT 14-fold over control; styrene treatment induced MT 2.5-fold. The MT induction by styrene could be attributed to decreased food intake, as a similar level of induction was observed in a pair-fed untreated control group. However, the level of MT induction by urethane was much greater than that produced by decreased food intake alone. Hepatic Zn concentration, particularly in the cytosol, was increased in the presence of increased hepatic MT concentration. Plasma Zn concentration was significantly decreased (approximately 30%) by urethane treatment, but not by styrene or food restriction (pair-feeding). Distribution of 65Zn to the liver of urethane-treated dams was significantly greater (by 30%), while distribution to embryonic tissues was significantly lower (by at least 50%) than in pair-fed or ad lib.-fed controls. Styrene treatment had no effect on 65Zn distribution. Urethane was developmentally toxic, causing an 18% decrease in fetal weight and a significant delay in skeletal ossification, but was not toxic to rat embryos in vitro. Styrene was not developmentally toxic. The changes observed after urethane treatment, namely substantial hepatic MT induction and altered maternal and embryonic Zn status, along with the lack of direct embryotoxicity of urethane in vitro, support the hypothesis that these maternal effects contribute to developmental toxicity. The lack of similar changes in styrene-intoxicated dams provides one explanation for its low developmental toxicity at maternally toxic dosages.

Chick embryo neural retina cell culture as a screen for developmental toxicity

An in vitro screen for developmental toxic potential of chemicals using primary cultures of chick embryo neural retina cells is described. The neural retinas of incubation Day 6.5 White Leghorn chick embryos are dissociated into single cells, which are subsequently maintained in a rotating suspension culture. Under normal circumstances, neural retina cells form spheroidal aggregates of a consistent size over the first 24 hr of culture, an event which is dependent on competent cell-cell interactions. Over the remaining 7-day period of culture, cells continue to divide and grow, and differentiation takes place. Each of these developmentally important events--aggregation, growth, and differentiation--is objectively and quantitatively measured as aggregate size and number, aggregate protein content, and glutamine synthetase (a marker of differentiation) activity, respectively. The effects on each developmental endpoint of 22 chemicals, 14 of which have been demonstrated to be developmentally toxic in one or more mammalian species in vivo, and 8 of which are not developmentally toxic, were evaluated. Chemicals were tested up to a concentration of 40 mM, or until marked cytolethality was observed. Of the known developmental toxicants, all but one, 2-methoxyethanol, affected one or more endpoints in the assay. The teratogenic metabolite of 2-methoxyethanol, 2-methoxyacetic acid, was active in the assay. None of the 8 nondevelopmental toxicants had any effect up to a concentration of 40 mM, or at biologically achievable concentrations (e.g., in vivo systemic concentrations at the LD50). Thus, the assay is 95% concordant with in vivo results for this set of chemicals. Quantitative comparisons were made (1) between developmentally toxic ip dosages in rats or mice in vivo and effective concentrations in the chick retina cell culture, and (2) between effective concentrations in chick retina cell culture and rodent whole embryo culture. In the first instance, 71% of the comparisons, and in the second instance, 89% of the comparisons, were within the same order of magnitude (and usually within a factor of two), indicating that the chick retina cell culture is also concordant with developmental toxic potency. Last, it was observed that test agents differentially affect developmental endpoints. Because the assay's endpoints are measured separately and objectively, it may be possible to use the assay to evaluate the effects of test agents on cellular development.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of lysosomal proteinase inhibition on the development of the rat embryo in vitro

Altered lysosomal function in the visceral yolk sac can result in abnormal development. As proteolysis is an important function of the rodent visceral yolk sac during early and mid-gestation, we characterized the lysosomal proteolytic enzyme activity of this extraembryonic membrane and determined the effects of inhibitors of protein degradation on embryonic development. Constituent activities of cysteine and aspartic acid proteinases were measured in rat visceral yolk sac on gestation day 12, and the effects of the cysteine proteinase inhibitors leupeptin, E-64 [trans-epoxysuccinyl-l-leucylamido(4-guanido)butane] and N-ethylmaleimide and the aspartic acid proteinase inhibitor pepstatin were determined in Sprague-Dawley rat embryos cultured in vitro from gestation days 10-12. It was determined that only cysteine proteinases, primarily cathepsins B and L, are active in the mid-gestation visceral yolk sac. The cysteine proteinase inhibitors leupeptin and E-64 both produced a concentration-related decrease in embryonic growth, as measured by crown-rump length, somite number, and embryonic protein content, and a concentration-related increase in incidence of abnormalities. A characteristic pattern of abnormalities was produced which involved a decrease in neural tube volume and the formation of a subectodermal blister opposite the point of attachment of the vitelline vessels. At high concentrations, anophthalmia was also observed. The decreased neural tube volume was associated with increased osmolality of the exocoelomic fluid, the major extraembryonic fluid compartment. It is possible that the osmotic change decreased neural tube volume by causing water to move to the compartment with a higher solute concentration, out of the embryo.(ABSTRACT TRUNCATED AT 250 WORDS)

Embryonal disposition of salicylate: in vivo-in vitro comparisons

The distribution of salicylate to embryonal compartments for in situ and in vitro rat embryos under equivalent exposure conditions, and salicylate disposition in the in vivo mid-gestation embryo and late gestation fetus, were compared. Pregnant Sprague-Dawley CD rats were exposed to steady-state blood levels of salicylate by infusing 14C-salicylic acid iv for a 24 hour period from gestation day 11.5 to 12.5. Cultured Sprague-Dawley rat embryos (in medium consisting of 100% male rat serum) were exposed to the steady-state 14C-salicylate concentration achieved in maternal serum in vivo for the same 24 hour developmental period. At the end of the exposure period radioactivity in visceral yolk sac, extra-embryonic fluid and embryos, and in maternal tissues, was measured. The distribution of salicylate to embryonal tissues was statistically comparable in vivo and in vitro, although the embryos in vitro accumulated slightly (but not significantly) less of the chemical. There was considerable binding of salicylate by maternal serum and culture medium proteins: less than 20% of the chemical was free at the 40 micrograms/ml concentration used in this experiment. Consequently, the salicylate concentration in embryonal compartments appeared to be quite low when compared to the surrounding serum/medium, but was actually equal to or greater than the concentration of unbound salicylate in serum or culture medium. The proportion of free salicylate in serum increased at concentrations higher than 40 micrograms/ml, resulting in somewhat higher concentrations of salicylate in in vitro embryos and extraembryonic fluid (as compared to medium) when cultured in the presence of 200 or 400 micrograms/ml salicylate.(ABSTRACT TRUNCATED AT 250 WORDS)

Difference in teratogenic potency of ethylenethiourea in rats and mice: relative contribution of embryonic and maternal factors

Ethylenethiourea (ETU) is a potent teratogen in the rat but not in the mouse or any other species tested. Embryotoxic and teratogenic effects are produced in mice only after exposure to 10-40 times the teratogenic dose of ETU in rats. This study was undertaken to determine whether the difference in sensitivity between rats and mice is due to differences within the embryo, to maternal metabolic differences, or both. Comparably staged rat and mouse embryos (gestation day 10.5 and 8.5, respectively) with intact extra-embryonic membranes were maintained under identical conditions in whole embryo culture and exposed to static concentrations of ETU for 48 hours. The teratogenic effects of ETU were qualitatively similar in both species, characterized by excessive fluid accumulations in embryonic structures. The most common abnormalities were distended neural tube, especially in the hindbrain, and clear blisters on the caudal region. At least two times as much ETU was required to produce a similar incidence of abnormalities in mice as in rats. Thus, there is some intrinsic difference in the quantitative response of rat and mouse embryos to ETU, but it is insufficient to account for the in vivo discrepancy. The role of maternal metabolism in modifying the teratogenicity of ETU was assessed by adding hepatic S-9 fractions from Aroclor 1254-induced rats and mice to whole embryo culture. Rat S-9 had no effect on ETU teratogenicity. Mouse S-9 virtually eliminated the formation of abnormalities typical of ETU in both rat and mouse embryos. Decreased exocoelomic fluid osmolality, a physiological effect produced by ETU, also was not observed in embryos exposed to ETU and mouse S-9. ETU-typical defects were observed in embryos exposed to ETU and mouse S-9 which had been treated with carbon monoxide to inactivate its monooxygenase system, indicating that the mouse S-9 was metabolizing ETU. A surprising result was that adding mouse S-9 to embryo cultures containing ETU resulted in the formation of abnormalities (principally open neural tube) that were not observed in in vitro rat or mouse embryos exposed to ETU alone, or in mouse embryos in vivo. We believe that the most likely cause of these abnormalities is a putative ETU metabolite, which is rapidly excreted by the dam in vivo, but accumulates to teratogenic concentrations in vitro.

Studies of the developmental toxicity of polycarboxylate dispersing agents

Three linear polycarboxylate compounds, two linear polyacrylates (90,000 MW and 4,500 MW) and one linear polyacrylate-maleate copolymer (12,000 MW), were tested for their teratogenic potential in female Sprague Dawley rats. These polymers, which were tested as sodium salts, are used as dispersing agents in detergent formulations at levels of 1-5%. All compounds were administered by gavage during organogenesis (days 6-15 of pregnancy). No adverse effects on development were seen with any of the three compounds at any of the doses tested. The highest dose, and therefore the minimum no-effect dose, for the three linear polymers was 1125 mg/kg/day for the 90,000 MW polyacrylate, 3000 mg/kg/day for the 4,500 MW polyacrylate, and 6670 mg/kg/day for the polyacrylate-maleate copolymer. Based on these data, these compounds are not developmentally toxic, even at very high dose levels.

Evaluation of the developmental toxicity of succinate tartrates in rats

The potential for succinate tartrates (ST) to induce developmental toxicity in Sprague-Dawley CD rats has been evaluated. ST dose levels of 250, 500 and 1000 mg/kg body weight/day were administered in the drinking-water on days 6-15 of gestation. Control animals received distilled water. Caesarean sections were performed on gestation day 20 and the foetuses were removed for teratological evaluation. No significant maternal or developmental toxicity was observed at any dose level. Based on these observations, the no-observed-effect level for ST developmental toxicity is greater than or equal to 1 g/kg/day, which was the highest dose tested.

Functional teratogens of the rat kidney. I. Colchicine, dinoseb, and methyl salicylate

Substances known or suspected to cause subtle or transient anatomical alterations in renal development were administered prenatally or neonatally to rats in order to determine whether they are capable of altering renal functional development. Colchicine alters mitotic activity and cytoskeletal structure and is teratogenic in many species. Since the kidney of the newborn rat undergoes extensive cellular proliferation and nephron differentiation, it is possible that neonatal administration of colchicine may affect nephron development. Dinoseb and methyl salicylate have previously been reported to produce a high incidence of dilated renal pelvis in the term rat fetus. Colchicine was injected sc, at 75 micrograms/kg, to Postnatal Day (PD) 1 Sprague-Dawley rats. Dinoseb was administered ip to pregnant Sprague-Dawley rats on Gestation Days 10-12 at doses of 8 or 10.5 mg/kg/day, and methyl salicylate was administered ip at doses of 200, 250, or 300 mg/kg/day on Gestation Days 11-12. Renal function was examined in pups from immediately after birth through weaning. Maximal urine concentrating ability was measured after DDAVP (desmopressin acetate, a vasopressin analog) injection in suckling rats, and after 24 hr of water deprivation in weanlings. Proximal tubule transport was measured in renal cortical slices. Basal urinary parameters, including urine flow, osmolality, pH, and chloride content, were measured. Colchicine treatment had no effect on body weight or kidney weight. There was a significant decrease in maximal urine osmolality in PD 30 rats measured after 24 hr of water deprivation. The urine concentrating deficit detected in functionally mature PD 30 rats suggests that colchicine treatment during renal histogenesis causes a latent deficit in medullary function in the absence of any gross morphological effects. The 10.5 mg/kg/day dose of dinoseb caused a weight reduction in neonates which persisted after weaning. Urine volume after DDAVP challenge was increased over controls in both dose groups on PD 6, but maximal urine concentration was unaffected. On PD 14, maximal urine concentration after DDAVP injection was decreased in the 10.5 mg/kg/day group. By PD 30, urine concentrating ability was comparable to controls. Renal cortical slices from the 10.5 mg/kg/day dose group had an enhanced ability to accumulate organic anions on PD 3 and 31, but opposite effects were observed in the low-dose group. No other renal functional parameters were altered. Urine osmolality after DDAVP challenge was decreased over controls in the 250 mg/kg/day methyl salicylate group on PD 6, and urine volume was increased in this group after DDAVP injection on PD 14.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional teratogens of the rat kidney. II. Nitrofen and ethylenethiourea

Nitrofen and ethylenethiourea (ETU), agents known to prenatally induce hydronephrosis in rats, were assessed for their effects on postnatal renal functional maturation. Both were given by gavage to pregnant Sprague-Dawley rats on Gestation Day 11. Nitrofen was given at concentrations of 50 or 100 mg/kg, and ETU at 20, 40, or 60 mg/kg. Renal function was examined in the offspring from birth until after weaning, the period of renal functional maturation in the rat. Maximal urine concentrating ability was measured after DDAVP (desmopressin acetate, a vasopressin analog) challenge or water deprivation. Proximal tubule transport was measured in renal cortical slices. Various urinary parameters were measured. Both prenatal nitrofen and ETU exposure caused a large number of neonatal deaths at the high dose, and hydronephrosis was observed. The severity of the lesion increased with age. Hydronephrotic animals were deficient in urine concentrating ability, which became more pronounced after weaning. A few other urinary parameters were altered, but cortical function appeared to be unaffected. Rats prenatally exposed to nitrofen, but with apparently normal kidneys, were significantly compromised in their ability to produce a concentrated urine in response to DDAVP challenge, on Postnatal Days (PDs) 6 and 14. By PD 30, they were not different from controls in urine concentrating response. Rats prenatally exposed to the higher doses of ETU, but with grossly normal kidneys, had significantly decreased plasma clearances of certain electrolytes early in life, but by PD 27, they were not different from controls. Proximal tubule transport of PAH was increased on PD 7 in ETU-exposed pups, but this effect did not persist.

Magnetic resonance imaging of congenital hydrocephalus in the rat

Magnetic resonance imaging (MRI) is an increasingly available technique in clinical medicine for the noninvasive imaging of soft tissues. The purpose of the present study was to demonstrate the potential utility of MRI in experimental toxicology and teratology studies. The progression of severity of prenatally induced hydrocephalus was observed in rat pups from 1 to 4 weeks of age. Pregnant Sprague-Dawley rats were given 0, 15, 30, or 45 mg/kg ethylenethiourea (ETU), po, on Gestation Day 15. The two higher doses have been reported to induce a high incidence of hydrocephalus, which is mild at birth but becomes extensive by 4 weeks of age. The low dose was a no effect level for hydrocephalus. None of the doses of ETU altered birth weight or litter size. Pups from each dose group were imaged serially, on Postnatal Days (PD) 6, 13, 17, and 27, in order to determine the progression in the severity of hydrocephalus. Littermates were also imaged on each of these days, then killed immediately in order to compare the anatomy of the brain with its MR image. Hydrocephalus was detectable in the images from all animals of the 30 and 45 mg/kg dose groups on PD 6, the earliest observation day. At this time, the lateral ventricles were dilated less than 1 mm. Hydrocephalus became increasingly severe, and by 4 weeks of age all of the 45 mg/kg group and approximately half of the 30 mg/kg group had died. The brains of the surviving 30 mg/kg rats were severely hydrocephalic, with little cortex remaining. In all cases, the MR image corresponded precisely with the brain anatomy observed after termination. We have demonstrated that MRI is a useful technique for noninvasively imaging lesions in experimental animals. A number of other potential uses for MRI in toxicology are presented.

In vitro teratogenicity of ethylenethiourea in the rat

We have demonstrated that ethylenethiourea (ETU) is a potent teratogen to the rat embryo developing in vitro. Sprague Dawley rat embryos were explanted on gestation day 10 and cultured for 48 hours in the presence of 40-200 micrograms/ml ETU. This resulted in a dose-related inhibition of growth and differentiation as assessed by crown-rump length, protein and DNA content, and somite number and in an increase in the frequency of abnormalities. A variety of anomalies was produced, including fluid accumulation in the brain (hydrocephalus), decreased mandibular size, decreased telencephalon size, abnormal dorsiflexion, as well as subectodermal blisters on the tail and limb buds and maxilla. Frank malformations have been observed at these same sites--hydrocephalus, brachygnathia, kyphosis, limb and tail defects, cleft palate--in the term fetus in vivo. The presence of abnormal fluid accumulation in the embryos--distended neural tube and subectodermal blisters--suggesting that the osmotic environment of the embryo had been altered by ETU exposure. Osmolality of the exocoelomic fluid (ECF) surrounding the embryo was measured after 48 hours of exposure to a concentration of ETU that caused nearly a 100% incidence of subectodermal blisters. ECF osmolality was found to be significantly lower than that of control embryos. Lowered osmolality would cause water to move out of the ECF, presumably causing the observed fluid accumulation in the embryo. It is speculated that altered osmotic balance and localized edema in the embryo are contributory steps in the formation of defects after ETU exposure.

Toxicity of mercuric chloride to the developing rat kidney. III. Distribution and elimination of mercury during postnatal maturation

Mercuric chloride is a potent nephrotoxicant in the adult rat, but has little effect on newborns. Nephrotoxicity increases with postnatal maturation. This study assesses the changes in tissue distribution and excretion of Hg during postnatal development. Sprague-Dawley rats were injected sc with 5 mg/kg 203HgCl2 on postnatal Day 1, 8, 15, 22, or 29. Hg concentration was measured in the whole body, renal cortex, medulla and papilla, liver, and subcellular fractions of liver and kidney. Binding to cytosolic metallothionein was assessed. Whole-body elimination of Hg was slow at the three younger age groups, as only 20% of the initial load was eliminated by 5 days after injection. Excretion was much more rapid in the two older groups, which eliminated about half of the initial load within 5 days. Concentration of Hg was highest in renal cortex (the principal site of Hg toxicity), and there was an age-related increase in cortical Hg concentration. This may explain the increased toxicity of Hg with age. There was an age-related decrease in hepatic Hg concentration. The high levels of metallothionein present in perinatal rat liver may protect the renal cortex from receiving a toxic dose of Hg; however, the increased concentration of hepatic Hg in newborns is insufficient to account for all of the cortical decrease. It is probable that Hg was distributed to other tissues. In liver and kidney cells of neonates, Hg concentration was highest in the cytosol, decreasing in an age-related manner. This was accompanied by an age-related increase of Hg in the nuclear/mitochondrial fraction. Hg in the cytosol was largely bound to metallothionein, although there were substantial amounts associated with very low-molecular-weight molecules and high-molecular-weight proteins. There are significant maturational changes in the organ, cellular and subcellular distribution of Hg in the rat during the first 4 weeks after birth. These probably explain the increasing sensitivity with maturity to Hg nephrotoxicity.

Studies on the mechanism of trypan blue teratogenicity in the rat developing in vivo and in vitro

Trypan blue is a potent teratogen in vivo and in vitro in the rat. Many of the abnormalities produced by trypan blue--including swollen neural tube and pericardium, subectodermal blisters, hematomas, and generalized edema--may result from altered fluid balance in and around the embryo. The present study demonstrates relationships between changes in the fluid environment around the embryo and appearance of anomalies. Rat embryos were exposed in utero or in vitro to trypan blue during the early period of organogenesis. Both exposures resulted in defects that are typical of trypan blue treatment. Osmolality of exocoelomic fluid (ECF) was measured on gestation day 10 in vivo and day 12 in vitro, both after 48 hr of exposure to trypan blue. In both cases ECF osmolality was significantly lower than controls. This was correlated with the presence of edema-related anomalies in the embryo. On gestation day 11 in vivo, three days after maternal injection of trypan blue, ECF osmolalities were significantly higher than controls; however, there was tremendous variability in this parameter in day 11 treated embryos, and some had ECF osmolalities below the control range. Increased frequency of abnormalities was correlated with abnormal ECF osmolality, below and above the control range. Trypan blue probably exerts its teratogenic effects by disturbing the function of the visceral yolk sac. The movements of an amino acid and a monosaccharide across the visceral yolk sac were measured on gestation day 12 embryos in vitro. This aspect of yolk sac function was not altered by trypan blue exposure. Ultrastructure of the visceral yolk sac was observed after trypan blue exposure in vivo and in vitro. Endodermal cells in trypan blue-treated yolk sacs contained fewer large, electron dense lysosomes than controls. These were replaced by numerous small vacuoles, which may contain trypan blue. Trypan blue causes osmotic changes in the rat embryo in vivo and in vitro. These changes are correlated with embryonic malformations. Alterations in yolk sac ultrastructure indicate that trypan blue affects the function of this membrane.

Toxicity of mercuric chloride to the developing rat kidney. II. Effect of increased dosages on renal function in suckling pups

It has been demonstrated that the sensitivity to HgCl2 nephrotoxicity increases with maturity in the rat, and that neonates are largely unaffected by a dose of 5 mg/kg. In the present study, immature rat pups were exposed to higher doses of HgCl2 to determine whether this effect was attributable to a quantitative or qualitative difference in the renal sensitivity to HgCl2. Sprague-Dawley rats were injected with a single dose of 5, 7.5, 10, 12.5, 20, or 30 mg/kg on Postnatal Day 1; 5, 7.5, 10, 12.5, 15, or 20 mg/kg on Day 8; or 6.25, 7.5, 10, or 12.5 mg/kg on Day 15. Renal function was evaluated at 24, 48, and 120 hr after treatment by measuring urine volume, osmolality, urinary pH, and chloride content, the ability to concentrate urine during water deprivation, and the presence of protein, glucose, or hemoglobin in urine. Animals were then killed and their kidneys weighed. A dose of 20 mg/kg was needed to induce mortality in pups treated at 1 day of age, and 15 mg/kg was needed in pups treated at 8 days of age. In contrast, the 6.25-mg/kg dose given to 15-day-old pups produced some mortality, and all rats given higher doses at 15 days of age died within 2 days. There was marked oliguria or anuria in the rats that died. Kidney weight was increased in a dose-related fashion at all ages. In those animals not rendered oliguric by the treatment, urine volume increased and the ability to secrete a more concentrated urine during water deprivation decreased. Urinary pH was decreased in a dose-related manner. Urinary chloride excretion was temporarily decreased after HgCl2 treatment on Day 1 , but was increased thereafter. Proteinuria, glucosuria, and hematuria were detected in the treated rats, again increasing in frequency and severity with age and dose.

Toxicity of mercuric chloride to the developing rat kidney. I. Postnatal ontogeny of renal sensitivity

Although the sensitivity of the adult rat kidney to mercuric chloride has been widely reported, the degree to which this toxicant affects the developing kidney is unknown. Therefore, this study examined the effects of HgCl2 on renal function during postnatal maturation. Sprague-Dawley rats were treated with a single sc injection of 5 mg/kg HgCl2 on Day 1, 8, 15, 22, or 29 after birth. The effects on renal function, histology, and morphology were assessed 24, 48, and 120 hr after each treatment. Measurements of renal function included urine volume, osmolality, the ability to concentrate urine during water deprivation, urinary pH, chloride and protein content, tests for glucosuria, hematuria, and various serum chemistry parameters. Rats were killed and their kidneys processed and examined by light microscopy. The renal sensitivity to HgCl2 increased throughout maturation for every parameter measured. No pups treated with HgCl2 on Day 1 died, but mortality increased to almost 20% in rats treated 22 and 29 days after birth. Body weight was unaffected in Day 1 animals, but was decreased at 120 hr post-treatment in three of the other four age groups. Kidney weights were unaffected in 1- and 8-day olds, but were increased by 10 to 55% in rats that were 15, 22, and 29 days old. Urine volume was increased 48 to 72 hr following treatment at all ages. The ability to concentrate urine in response to water deprivation was compromised in all animals with the exception of those treated on Day 1, and was decreased to the greatest extent in 29-day-olds. Urinary chloride concentration was decreased in Day-22 animals at 24 and 48 hr, and in Day-29 rats at all times observed after injection. Urinary pH was more acidic in treated suckling pups, and more basic in treated pups after weaning on Day 22. Urinary protein content was increased after exposure in all but the pups treated on Day 1. Serum creatinine was increased at 120 hr after injection in Day-8 rats, and 24 and 48 hr after injection in older rats. Glucosuria and hematuria occurred with increasing frequency as the pups matured. Histological evaluation revealed some cortical tubular dilatation in rats treated on Day 1 or Day 8; there was tubular necrosis in older rats. For all parameters observed, the neonatal kidney was largely insensitive to HgCl2 toxicity; however, a trend toward increased sensitivity with increasing age was demonstrated.

Toxic effects of cadmium on the developing rat lung. II. Glycogen and phospholipid metabolism

Maternal exposure to Cd reduces lung weight and alters pulmonary surfactant accumulation in the fetus. This may lead to respiratory distress and death postnatally. In this study, the effects of maternal Cd administration on additional biochemical parameters of the fetal lung were investigated. Pregnant rats were given sc injections of 8 mg/kg CdCl2 on the 12-15 of gestation and sacrificed throughout late gestation. Fetal lungs were examined for protein, DNA, and glycogen. Incorporation of choline into total and disaturated phosphatidylcholine and sphingomyelin were measured in fetal lung slices. The DNA content of the treated lungs was reduced, but the protein/DNA ratio was not altered. Thus the reduced lung weight was due to hypoplasia, not hypotrophy. Incorporation of choline into pulmonary sphingomyelin was not altered by the treatment. Choline incorporation into both total and disaturated phosphatidylcholine, the most important surfactant component, was reduced on the final days of gestation. Glycogen was reduced in both absolute quantity and cellular concentration of lungs of treated fetuses. Glucose derived from glycogen is a major metabolic substrate in the fetal lung and probably contributes greatly to phospholipid synthesis. The reduction in glucose concentration in lungs of treated fetuses may be a factor in the diminished synthesis of pulmonary surfactant phosphatidylcholine before birth. Prenatal Cd exposure (1) causes pulmonary hypoplasia, (2) reduces the amount of glycogen present in the fetal lung, and (3) diminishes the rate of synthesis of pulmonary surfactant phosphatidylcholine.

Fetal zinc deficiency as a mechanism for cadmium induced toxicity to the developing rat lung and pulmonary surfactant

Maternal exposure to cadmium alters lung and pulmonary surfactant development in the rat fetus. A toxic property of cadmium is its biological interaction with the essential trace metal zinc. The present study was undertaken to determine the role of zinc in the induction of fetal anomalies by cadmium. Pregnant rats were injected with 8 mg/kg cadmium chloride alone or with 12 mg/kg zinc chloride on gestation days 12-15 and sacrificed on gestation day 21. Controls received injections of saline and zinc chloride. Pulmonary surfactant phospholipids were isolated from fetal lungs and quantified. Concentrations of cadmium and zinc in maternal and fetal tissues and placenta were measured. Cadmium treatment caused embryonic death, lung hypoplasia and diminished quantity of the major pulmonary surfactant phospholipid, phosphatidylcholine. Zinc treatment alone did not alter normal fetal development. Coadministration of zinc with cadmium prevented all of the previously observed cadmium-induced fetotoxicity. The placenta appeared to act as a barrier to cadmium movement, as cadmium was found in the placenta but not in fetal tissues. However, cadmium treatment decreased fetal zinc content. Simultaneous injection of zinc with cadmium maintained the fetal zinc concentration at the control level. Thus cadmium appears to exert its fetotoxic effects indirectly, through a fetal zinc deficiency.

Toxicity of minimal amounts of cadmium to the developing rat lung and pulmonary surfactant

Pregnant rats were injected subcutaneously with 0, 1, 2, 4 or 8 mg cadmium chloride/kg each day during mid-gestation from day 12-15. Dams were sacrificed on day 21. The treatment resulted in a dose-related increase in prenatal mortality, and decreases in body weight, lung weight and saturated fatty acid containing lecithin content in the fetus but no change in pulmonary sphingomyelin. Although the lowest dose produced no changes in fetal viability, body weight or lung weight, a significant reduction in the amount of saturated fatty acid containing lecithin occurred. Since saturated fatty acid containing lecithin is a major component of pulmonary surfactant, fetuses from CdCl2-treated dams may be subject to respiratory distress postnatally.

Effects of cadmium on the prenatal ultrastructural maturation of rat alveolar epithelium

Maternal administration of cadmium (Cd) has previously been shown to cause reduced lung weight and altered pulmonary surfactant accumulation in fetal rats. This leads to neonatal respiratory distress. In the present study the effects of Cd on the ultrastructural development of alveolar epithelium was studied to detect any alterations which could contribute to neonatal respiratory difficulties. Pregnant rats received 8.0 mg/kg body weight of CdCl2 subcutaneously on days 12-15 of gestation. Fetal tissue was examined by electron microscopy throughout the period of alveolar cytodifferentiation. The undifferentiated epithelium of both treated and control fetuses was composed of simple columnar cells with apical and basal glycogen deposits. Cytodifferentiation in controls consisted of gradual flattening of alveolar type I cells and the appearance of surfactant-containing lamellar bodies in alveolar type II cells. Cytoplasmic glycogen was prominent up to day 20, then diminished to low levels on day 21. Epithelial differentiation in treated fetuses was delayed in most alveoli. On the two days before term some alveoli appeared normal, but many were retarded or arrested in their development. Cellular glycogen pools were reduced in treated alveoli and were absent just prior to birth. Lamellar bodies in treated alveoli were less numerous, correlating with the diminished pulmonary surfactant lecithin content reported earlier. These alterations in prenatal ultrastructural maturation could contribute to the postnatal respiratory difficulties previously observed.

Toxic effects of cadmium on the developing rat lung. I. Altered pulmonary surfactant and the induction of respiratory distress syndrome

The effects of Cd on the growth of the fetal rat lung and the maturation of the pulmonary surfactant system were studied. Pregnant rats received sc injections of cadmium chloride on d 12-15 of gestation. Animals were sacrificed throughout late gestation. Fetal lungs were assayed for pulmonary surfactant lecithin and spingomyelin. Some animals were allowed to give birth and the neonates were observed for symptoms of respiratory distress. The treatment resulted in high fetal mortality and growth retardation. Lung-body weight ratios were reduced by 20-30% in treated fetuses. Pulmonary spingomyelin content was not affected by the Cd absolute quantity but not in lecithin-lung weight ratio on the last days of gestation. Parturition was delayed almost a full day by the Dd treatment, and birth weights were reduced. Of the treated neonates, 11% developed respiratory distress syndrome. All but one of these individuals died and had lungs with hyaline membranes. Prenatal exposure to Cd can (1) cause lung hypoplasia, (2) affect pulmonary surfactant, and (3) induce respiratory distress syndrome in term pups.