Toluene toxicokinetics and metabolism parameters in the rat and guinea pig.

Cochlear disruptions induced by toluene were shown in the rat but not in the guinea pig. To better understand the differences between species, three investigations were carried out to study (1) the blood affinity and the pulmonary uptake of the solvent, (2) its clearance and (3) its urinary elimination in both species. The blood affinity of toluene was +44% higher in the rat than in the guinea pig (14.4µg/g versus 10µg/g). Similarly, the pulmonary uptake of toluene was approximately 46.5% more efficient in the rat than in the guinea pig (75.4µg/g versus 40.3µg/g) after 3h inhalation of 1500ppm toluene. Therefore, the physicochemical composition of the blood could explain the difference in the uptake performances between rats and guinea pigs. The clearance of the toluene showed that 10min after an intravenous administration of 400µL of vehicle containing 28µL (43mgkg(-1)) of toluene, the solvent concentration was approximately threefold higher in the rat than in the guinea pig blood. The last experiment was carried out to compare the concentrations of the urinary metabolites. The concentrations of o-cresol, hippuric and benzyl mercapturic acids measured in the urines were different before and after the toluene injection. These data give evidence for large differences of toluene uptake and metabolism between rat and guinea pig. Therefore, it seems reasonable to claim that guinea pigs cochleas are not susceptible to toluene as the blood burden of solvent does not reach the concentration required to induce permanent damages.

Toxicokinetic parameters of toluene in the rat and guinea pig: a comparative study.

Toluene is the most widely used industrial solvent. It has been shown to cause cochlear disruptions in rats but markedly less ototoxic effects in guinea pigs. Susceptibility to the ototoxic properties of toluene is, therefore, species specific. In recent publications, an important difference in the solvent concentration in blood has been identified when rats and guinea pigs were exposed in strictly identical experimental conditions. Solvent concentrations in blood were greater in rats than in guinea pigs. The present studies were designed to compare blood affinity and toxicokinetic parameters of toluene in an attempt to understand the susceptibility differences in both species. The in vitro experiment, in which the headspace concentration of toluene was measured within a sealed vial containing blood, highlighted the greater toluene partition coefficient in rat than in guinea pig blood. The in vivo experiment showed that 10min after a single intravenous administration of 28µL of toluene, the solvent concentration is approximately two-fold lower in guinea pig than in rat blood. Based on the toxicokinetic parameters of toluene and on the relative partition coefficient of toluene in blood, it seems plausible that guinea pigs are not susceptible to organic solvents because the solvent concentration in blood does not reach the concentration required to induce permanent damage. Attempts to explain differences of vulnerability between the rat and guinea pig are addressed in the present paper.

Assessment of the developmental toxicity, metabolism, and placental transfer of Di-n-butyl phthalate administered to pregnant rats.

The developmental toxicity and placental transfer of di-n-butyl phthalate (DBP) were evaluated in Sprague-Dawley rats given a single oral dose of DBP on Gestational Day 14. In the developmental toxicity study, dams were dosed with 0, 0.5, 1, 1.5, or 2 g DBP/kg and were necropsied on GD21. Increased incidence of resorptions and reduced fetal body weight were observed at 1.5 and 2 g/kg. Higher incidences of skeletal variations were found at doses > or = at 1 g/kg. No embryotoxic or teratogenic effects were observed at a dose of 0.5 g/kg. In the placental transfer study, dams were dosed with 0.5 or 1.5 g [14C]DBP/kg. Maternal and embryonic tissues were collected at intervals from 0.5 to 48 h. Embryonic tissues accounted for less than 0.12-0.15% of the administered dose. Levels of radiocarbon in placenta and embryo were one-third or less of those in maternal plasma. No accumulation of radioactivity was observed in the maternal or embryonic tissues. From HPLC analyses, it was shown that unchanged DBP and its metabolites mono-n-butyl phthalate (MBP) and MBP glucuronide were rapidly transferred to the embryonic tissues, where their levels were constantly lower than those in maternal plasma. MBP accounted for most of the radioactivity recovered in maternal plasma, placenta, and embryo. Unchanged DBP was found only in small amounts. These findings support the hypothesis that MBP, a potent teratogen, largely contributes to the embryotoxic effects of DBP.

Pregnancy-associated changes in renal toxicity of cadmium-metallothionein: possible role of intracellular metallothionein.

Nulliparous female, 10-day and 20-day pregnant rats were injected intraperitoneally with saline or labelled cadmium-metallothionein (109Cd-MTh) at a single dose of 25 or 250 micrograms Cd as cadmium-metallothionein (Cd-MTh)/kg and sacrificed at 24 h. The renal toxicity was manifested by increased 24-h urinary excretion of beta 2-microglobulin (beta 2-m) and the increased number of damaged convoluted proximal tubules at 24 h. The renal excretion of 109Cd and 109Cd content in the maternal liver and kidney and in the foeto-placental unit were determined. The binding of 109Cd to kidney proteins and the level of intracellular metallothionein (MTh) in livers and kidneys were also determined. It was found that the nephrotoxicity of injected Cd-MTh did not differ in nulliparous and 10-day pregnant rats. This result was consistent with the absence of difference in the renal uptake of 109Cd, its binding to kidney proteins and in the content of endogenous MTh in the kidneys between nulliparous and 10-day pregnant rats. In contrast, 20-day pregnant rats exhibited much more nephrotoxicity than nulliparous rats. The most prominent finding in relation to the extreme sensitivity of 20-day pregnant rats was a lower basal level of intracellular MTh in the kidneys and the accumulation of 109Cd in the high molecular weight proteins in the soluble fraction. It is suggested that the decrease of intracellular MTh in the kidneys of 20-day pregnant rats is the reason for the low protection against the renal toxicity of injected Cd-MTh.

Assay of circulating hyaluronic acid in the rat: study of diurnal variation and effect of anesthesia.

Serum hyaluronic acid (HA) may provide a good marker for the severity of joint disease in the rat since a positive correlation was observed in experimental models of arthritis. However, little is known about its physiological variation in rats. In the present work, we do not find any circadian rhythm of HA in healthy Sprague-Dawley rats in contrast to that observed in humans, whose serum levels vary during daytime. Furthermore, the influence of blood sampling conditions on HA concentrations was evaluated in conscious animals and by using different anesthetics. The greater reproducibility for the assay of HA is observed with the intracardiac puncture under ether inhalation. Blood sample collection in the absence of anesthesia leads to a significant increase in serum levels of HA, which could be attributed partly to enhanced joint movements generated by psychological stress.

Assessment of urinary rat beta 2-microglobulin by enzyme immunoassay.

An enzyme immunoassay (EIA) was developed using unlabelled and peroxidase-labelled rabbit antibodies to assess urinary rat beta 2-microglobulin (beta 2-m) excretion. It consisted in the adsorption of rabbit anti-rat beta 2-m immunoglobulin to a polystyrene surface, the addition of beta 2-m samples or standard and the addition of peroxidase-labelled rabbit anti-rat beta 2-m immunoglobulin. After addition of hydrogen peroxide and o-phenylenediamine, the enzyme activity of the solid phase was measured photometrically at 490 nm. Analytical recovery of pure beta 2-m in urine was 102%. From determinations made on normal female and male rats, the ranges of 24-h urine beta 2-m individually excreted were found to be 0.84-4.77 and 3.7-17.3 micrograms, respectively. The means +/- SEM were 2.49 +/- 0.17 and 10.2 +/- 0.55 micrograms. EIA was of value in evidencing the tubule-damaging properties of sodium chromate and hexachloro-1,3-butadiene in rats.

A sensitive cadmium-affinity assay for the determination of thionein in urine.

A sensitive cadmium-affinity assay was developed for measurement of urinary thionein (Th) level. Acidification with HCl (2.5 M) was used to remove metal ions from purified urinary metallothionein (MTh), adsorbed on activated polystyrene tubes. It was found that the amount of 109Cd bound to standard Th (rabbit Th) was proportional to that of Th in the concentration range of 20-6000 ng/ml. The method exhibited a sensitivity below 20 ng/ml and a precision of about 5%. The results of the Cd-affinity assay were unaffected by dilution of, or addition of standard Th to urine samples. Under the latter circumstances, the Cd-affinity assay was performed with a mean analytical recovery of 100.3 +/- 4%. Addition of Cd, Zn, Hg and Cu (50 micrograms each) or glutathione and cysteine (0.1 mmol) to urine specimens (1 ml) did not interfere with the determination of Th. The mean values of urinary Th in healthy subjects were 200 +/- 53 micrograms/g creatinine (n = 9) and 256 +/- 97 micrograms/g creatinine (n = 8) for men and women respectively. The mean daily excretions of Th by non-fasting female and male healthy adult rats were 9.95 +/- 2.7 micrograms (n = 10) and 18.2 +/- 3.9 micrograms, respectively. The Cd-affinity assay succeeded in indicating Cd exposure and/or development of Cd toxicity in rats.

Assessment of the developmental toxicity and placental transfer of 1,2-diethylbenzene in rats.

Sprague-Dawley rats were administered 1,2-diethylbenzene (1,2-DEB) by gavage on gestational days (GD) 6 through 20 at dose levels of 0 (corn oil), 5, 15, 25 or 35 mg/kg. The dams were euthanized on GD21 and the offspring were weighed and examined for external, visceral and skeletal alterations. Maternal toxicity, indicated by significant decreases in body weight gain and food consumption, was observed at doses of 15 mg/kg and above. Developmental toxicity, expressed as significantly reduced foetal body weights, was seen at doses of 15 mg/kg and higher. There was no evidence of embryolethal or teratogenic effects at any dose tested. The placental transfer of 1,2-DEB was examined after a single oral dose of 25 mg [14C]1,2-DEB/kg on GD18. Maternal and foetal tissues were collected at intervals from 1 to 48 hours. Placental and foetal tissues accounted for less than 0.35% of the administered dose. Levels of radiocarbon in foetuses were lower than those in maternal plasma and placenta at all time points. Analysis performed at 1, 2 and 4 hours indicated that ethyl acetate extractable (acidic) metabolites were predominant in the maternal plasma while n-hexane extractable (neutral) compounds represented the major part of radioactivity in the placenta and foetus. In conclusion, this study demonstrated that 1,2-DEB causes mild foetotoxicity at maternal toxic doses and that the exposure of the developing rat foetus to 1,2-DEB and/or metabolites after maternal administration of 1,2-DEB in late gestation is small.

Creatinine normalization in biological monitoring revisited: the case of 1-hydroxypyrene.

OBJECTIVES: To compare the apparent urinary excretion rates of both creatinine and 1-hydroxypyrene (1-OHP) and to assess the value of creatinine normalization for both toxicokinetic analysis and the routine examination of workers. METHODS: All urine samples were collected from individuals who had been exposed to polycyclic aromatic hydrocarbons (PAHs), occupationally and non-occupationally, for at least 24 consecutive hours. Urinary creatinine and 1-OHP were determined. 1-OHP excretion rates were expressed either as a function of creatinine excretion rate or as unadjusted values. Theoretical relationships between creatinine-normalized excretion of metabolites and body weight-adjusted inhaled dose were drawn for men with a constant body mass index. RESULTS: Creatinine excretion rate paralleled 1-OHP excretion rate. The plot of creatinine excretion rate-adjusted excretion rate of 1-OHP vs time led to smooth curves for determination of toxicokinetic parameters. Creatinine normalization was adequate, even for samples with a urinary creatinine concentration below 0.5 g/l or above 3 g/l. A theoretical analysis revealed that men weighing between 50 kg and 100 kg, exposed to a constant dose of a pollutant producing a urinary metabolite excreted by the same mechanism as creatinine, would exhibit a body weight-adjusted dose span of 2 with an accompanying creatinine-normalized metabolite excretion span of 2.23-fold. CONCLUSION: The kinetics of creatinine excretion parallels that of 1-OHP, and a creatinine excretion rate-normalized excretion rate of 1-OHP appears to allow for a better determination of the toxicokinetic parameters of 1-OHP urinary excretion. At least in the case of 1-OHP, creatinine normalization seems valid, even for very dilute or very concentrated urine samples. Finally, because creatinine normalization not only compensates for variable diuresis but also correlates better with the body weight-adjusted dose of the parent compound, it should be used in biological monitoring of exposure to (PAHs) pyrene and to other substances whose urinary biomarker excretion kinetics parallel that of creatinine.

Polycyclic aromatic hydrocarbon exposure in an artificial shooting target factory: assessment of 1-hydroxypyrene urinary excretion as a biological indicator of exposure.

Five representative workers and two external observers were monitored by personal air and urinary 1-hydroxypyrene (PyOH) sampling for a four-shift working week in an artificial shooting target factory. The targets (clay pigeons), are made from petroleum pitch and molded at 190 degrees C. No respiratory protective mask was worn. Atmospheric concentrations of pyrene and benzo (a) pyrene (BaP) ranged from 0.66 to 5.05 microg/m(3) and 0.037 to 0.270 microg/m(3) respectively with a mean pyrene/BaP ratio of about 20 and a correlation r = 0.51. Maximum PyOH urinary excretion ranged from 1.84 to 10.9 micromol/molCreat. This occurred at the postshift for the observers but often appeared later for workers: up to 10.75 h for the person with the apparently highest dermal exposure. The apparent PyOH excretion half lives ranged from 1.9 to 12.5 h with an arithmetic mean of 6.1 h. All these data were confirmed by additional measurements taken over a weekend after the postshift. The correlation between atmospheric pyrene and urinary PyOH concentrations (increase over the shift) was poor (r = 0.37). It improve greatly (r = 0.74) if the amount of pyrene inhaled over the shift and the corresponding amount of PyOH excreted were considered. The ratio of urinary excreted PyOH to the pyrene inhaled dose (with assumed retention of 100%), ranged from 0.18 to 0.70 (arithmetic mean = 0.34). This suggests that the respiratory tract is the main entrance route for pyrene (apart from the worker who handled crude targets without gloves).

Biliary excretion of hexachloro-1,3-butadiene and its relevance to tissue uptake and renal excretion in male rats.

Renal, biliary, pulmonary and faecal excretion experiments were carried out with labelled hexachloro-1,3-butadiene [( 14C]HCBD) in male Sprague-Dawley rats, given orally (p.o.) and intravenously (i.v.) in doses of 1 and 100 mg kg-1 as a solution in polyethylene glycol. The radioactivity excreted over 72 h was determined in rats fitted with exteriorized biliary cannulae and in rats whose bile ducts remained fully functional, respectively. In addition, bile duct-duodenum cannula-linked rats, of which the donor was given 100 mg kg-1 [14C]HCBD orally and the recipient had also a bile fistula, were examined within 30 h for radioactivity in the excreta, the kidney, the liver and the plasma. In non-cannulated rats, fractional urinary excretion decreased when the dosage increased and amounted to 23% and 8.6% after i.v. injection or 18.5% and 8.9% after p.o. administration of 1 and 100 mg kg-1, respectively. Pulmonary excretion of radioactivity was less than 9% and was not affected by the increase in dosage. In bile duct-cannulated rats, fractional urinary excretions were similar irrespective of the dose and the route of administration and amounted to ca. 7.5% of the dose. Decrease in fractional biliary excretion occurred with increase in dosage (88.7% vs 72%) after i.v. injection and (66.8% vs 58%) after gavage. In cannulated rats, faecal excretion was less than 0.5% after i.v. injection and accounted for 3% and 16% of the dose after p.o. administration of 1 and 100 mg kg-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in urinary proximal tubule parameters in neonatal rats exposed to cadmium chloride during pregnancy.

Pregnant Sprague-Dawley rats were injected intraperitoneally with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.0 or 2.5 mg kg-1 on days 8, 10, 12 and 14 of gestation. On postnatal day (PND) 3, 12 or 49, the offspring were examined for 8- or 24-h urinary excretion of beta 2-microglobulin (beta 2-m), metallothionein (MT) and urinary activity of three proximal tubular enzymes: gammaglutamyl transferase (GGT), alkaline phosphatase (ALP) and N-acetyl-beta-glucosaminidase (NAG). Treatment with CdCl2 did not affect growth or survival of offspring. Significant decreases in the urinary excretion of GGT, ALP and NAG were observed on PND 3, at both doses. Exposure to 4 x 2.5 mg kg-1 resulted in functional deficit of the proximal tubule on PND 3, as evidenced by the significant increase in beta 2-m. Except for a slight but significant increase of beta 2-m in 49-day-old males, all the other urinary parameters returned to control values on PND 12. There was no effect on MT. Results from this study show that prenatal exposure to CdCl2 can induce significant changes in the kidney biochemistry of rats in the early postnatal period.

Role of extracellular glutathione and gamma-glutamyltranspeptidase in the disposition and kidney toxicity of inorganic mercury in rats.

The role of extracellular glutathione (GSH) and membrane-bound gamma-glutamyltranspeptidase (gamma-GT) as contributory factors in the disposition and toxicity of inorganic mercury (HgCl2, 1 mg kg-1, i.p.) was investigated in rats pretreated with acivicin (AT-125, 10 mg kg-1), a gamma-GT inhibitor. A high degree of gamma-GT inhibition (75%) and of protection (90%) against HgCl2-induced nephrotoxicity was obtained in gamma-GT-inhibited rats 24 h post-treatment. Pretreatment with acivicin affected the fractional distribution profile of 203 Hg, resulting in a twofold decrease in the renal incorporation of mercury 4 h post-treatment and a threefold increase in the 24-h urinary excretion of mercury. Plasma radioactivity remained constant over 24 h in rats dosed with 203Hg alone, whereas it decreased by 60% between 4 h and 24 h in gamma-GT-inhibited rats. In gamma-GT-inhibited rats treated with HgCl2 the renal and plasma reduced glutathione (GSH) content increased by 68% and 330% respectively, as compared to controls. The gamma-GT inhibition affected the distribution profile of mercury within urinary proteins, shifting the binding of mercury from the high-molecular-weight fraction (3% against 80%) to the low-molecular-weight fraction (72% against 10%). A significant but less impressive shift of mercury from the high- to the low-molecular-weight fraction also arose in the plasma. These results taken together support the pivotal role of extracellular GSH and membrane-bound gamma-GT in the renal incorporation, toxicity and excretion of inorganic mercury in rats.

Indirect and lactation-associated changes in renal alkaline phosphatase of newborn rats prenatally exposed to cadmium chloride.

Pregnant Sprague-Dawley rats were intraperitoneally injected with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.5 mg kg-1 body wt. on days 8, 10, 12 and 14 of gestation. Offspring were examined for renal alkaline phosphatase activity (ALP) on postnatal days (PND) 3 and 12, and for kidney metallothionein (MTh) and for liver, kidney and entire gastrointestinal tract 109Cd content at birth and on PND 3 and 12. No effects were observed on neonatal survival or on body, liver and kidney weights of pups up to PND 12. Newborns born and fed by mothers exposed to CdCl2 during pregnancy exhibited a significant decrease in ALP activity on PND 3. Conversely, no significant changes were observed in newborns lactated by surrogate non-treated mothers. Renal MTh increased with age but was not influenced by maternal treatment. Traces of 109Cd were present in the liver at birth (5-7 ng). Thereafter, 109Cd was mainly found in the gastrointestinal tract of newborns lactated by their biological mothers (610-690 ng on PND 12), with a marginal uptake in the liver (10-12 ng on PND 12). 109Cd was not detectable in the kidneys at any age (less than 4 ng). These results show that prenatal exposure to Cd cannot be the sole aetiological agent in the induction of the subtle and transitory changes in renal biochemistry observed in offspring born and fed by female rats intraperitoneally injected with 2.5 mg CdCl2 kg-1 body wt. on days 8, 10, 12 and 14 of gestation. The results also contradict the role of a direct effect on the kidney.

Toxicokinetics and metabolism of 1,2-diethylbenzene in male Sprague Dawley rats--part 2: evidence for in vitro and in vivo stereoselectivity of 1,2-diethylbenzene metabolism.

In a previous study, it was shown that the neurotoxic compound 1,2-diethylbenzene (1,2-DEB) is mainly hydroxylated in the alkyl chain to give 1-(2'-ethylphenyl)ethanol (1,2-EPE) and excreted in urine of rats as two glucuronide compounds (GA1 and GA2). Some findings have suggested that the two enantiomers of 1,2-EPE are formed in vivo. In the present study, a chiral high-performance liquid chromatography method was developed to separate the two enantiomers of 1,2-EPE from a synthesized racemic mixture. Absolute configuration of both enantiomers was determined after esterification with (R)-(+)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetic acid and analysis of their (1)H NMR spectra in CCl(4) added with Eu (fod)(3). The two main urinary metabolites, GA1 and GA2, from [(14)C]1,2-DEB-treated Sprague-Dawley rats (80 mg/kg, i.p.) were identified, after hydrolysis with beta-glucuronidase from Escherichia coli, as (R) and (S) glucuronide conjugates of 1,2-EPE, respectively. In vitro hydroxylation of 1,2-DEB and glucuroconjugation of 1,2-EPE were under stereoselective control in S9 fraction or microsomes from male Sprague-Dawley rat liver. The V(max) and K(m) constants for (R)1,2-EPE enantiomer formation determined in S9 fraction were greater than those for the (S) enantiomer. In the plasma of bile duct-cannulated rats, the ratio was 1.2 +/- 0.02 over the 1- to 4-h period after oral administration of [(14)C]1,2-DEB (100 mg/kg). In contrast, the glucuroconjugation rate of (S)1,2-DEB enantiomer was 4 times that of (R)1,2-EPE glucuroconjugation. A similar ratio of (R) to (S)1,2-EPE glucuronide conjugates was obtained in the plasma of bile duct-cannulated rats.

Toxicokinetics of 1,2-diethylbenzene in male Sprague-Dawley rats-part 1: excretion and metabolism of [(14)C]1,2-diethylbenzene.

The excretion and metabolism of neurotoxic 1,2-diethylbenzene (1, 2-DEB) was studied in male Sprague-Dawley rats after i.v. (1 mg/kg) or oral (1 or 100 mg/kg) administration of 1,2-diethyl[U-(14)C]benzene ([(14)C]1,2-DEB). Whatever the treatment, radioactivity was mainly excreted in urine (65-76% of the dose) and to a lower extent in feces (15-23% of the dose), or via exhaled air (3-5% of the dose). However, experiments with rats fitted with a biliary cannula demonstrated that about 52 to 64% of the administered doses (1 or 100 mg/kg) were initially excreted in bile. Biliary metabolites were extensively reabsorbed from the gut and ultimately excreted in urine after several enterohepatic circulations. Insignificant amounts of unchanged 1,2-DEB were recovered in the different excreta (urine, bile, and feces). As reported previously, presence of 1-(2'-ethylphenyl)ethanol (EPE) was confirmed in urine and demonstrated in bile and feces. The two main [(14)C]1,2-DEB metabolites accounted for 57 to 79% of urinary and biliary radioactivity, respectively. Beta-Glucuronidase hydrolysis and electron impact mass spectra results strongly supported their glucuronide structure. Additionally, these two main metabolites were thought to be the glucuronide conjugates of the two potential enantiomers of EPE. The results indicate that the main initial conversion step of the primary metabolic pathway of 1,2-DEB appears to be the hydroxylation of the alpha-carbon atom of the side chain. The presence of two glucuronide conjugates of EPE in the urine in a ratio different from one suggests that the metabolic conversion of 1, 2-DEB is under stereochemical control.

Urinary thiodiglycolic acid and thioether excretion in male rats dosed with 1,2-dichloroethane.

1,2-dichloroethane (DCE) is extensively metabolized and partially excreted in urine as thioether compounds, which include thiodiglycolic acid (TDGA). In this study, we have compared the urinary excretion of TDGA and thioethers in the rat after administration of increasing doses of DCE. Male Sprague Dawley rats were given a single oral dose of labelled [14C]DCE (0.125 to 8.08 mmol kg-1 body wt.) and 24-h urine samples were collected. The TDGA and thioethers were determined in urine by a gas chromatography method and by the thioether assay after alkaline hydrolysis, respectively. The percentage of the administered radioactivity that was excreted in urine decreased with increasing dose of DCE and ranged between 63 and 7.4%. The amount of TDGA increased proportionally to the DCE dose up to 1.01 mmol DCE kg-1 body wt. and corresponded to 0.22 mmol TDGA mmol-1 DCE. Up to 0.25 mmol DCE kg-1 body wt., the amount of thioethers recovered in urine was not significantly different as compared to the vehicle control group (11.8 +/- 0.6 mumol SH equiv. kg-1 body wt., n = 10). From the 0.25-4.04 mmol DCE kg-1 body wt. dose, the amount of thioethers increased linearly with the dose of DCE and corresponded to 0.028 mmol SH equiv. mmol-1 DCE. The ratio between urinary thioethers and TDGA increased with the DCE dose and reached 0.17 +/- 0.01 (n = 5) at a dose of 8.08 mmol DCE kg-1 body wt. Moreover, TDGA contents determined in urine by gas chromatography before and after alkaline hydrolysis were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific amino acids modulate the embryotoxicity of nickel chloride and its transfer to the rat embryo in vitro.

To investigate the effects of amino acids on the embryotoxicity and placental transfer of nickel chloride (NiCl2), Day 10 rat embryos were cultured in rat serum medium containing NiCl2 or 63NiCl2 (0.34 or 0.68 mM Ni), with or without L-histidine (2 mM), L-aspartic acid, glycine (2 or 8 mM), or L-cysteine (2 mM). After 26 hr, conceptuses were assessed for survival, growth and development, and malformations. The 63Ni contents of embryos and yolk sacs and the extent of 63Ni binding to the proteins of the culture medium were also determined. NiCl2 alone did not affect the embryonic development at 0.34 mM and caused growth retardation and brain and caudal abnormalities at 0.68 mM. Coincubation of L-histidine with 0.34 mM Ni increased Ni concentrations in embryonic tissues compared to 0.34 mM 63Ni alone, but did not elicit NiCl2 embryotoxicity. Coincubation of L-cysteine with 0.34 mM Ni elicited growth retardation and brain abnormalities caused by NiCl2 and increased yolk sac concentrations of 63Ni compared to 0.34 mM 63Ni alone. In contrast, coincubation of L-histidine, L-cysteine, or L-aspartic acid with 0.68 mM Ni reduced the growth retardation and the incidence and/or severity of brain defects caused by NiCl2 and decreased the concentrations of 63Ni in the yolk sacs, compared to 0.68 mM 63Ni alone. L-Histidine also reduced the percentage of NiCl2-elicited caudal defects. Coincubation with glycine did not NiCl2-elicited caudal defects. Coincubation with glycine did not affect the embryotoxic profile, nor the placental transfer of NiCl2. In the presence of L-histidine, L-cysteine, or L-aspartic acid, there was a shift of 63Ni binding from the high-molecular-weight proteins of the culture medium to the low-molecular-weight fraction. Thus, specific extracellular amino acids can modulate the embryotoxicity and placental transfer of NiCl2 in vitro. The pattern of this modulation is dependent on the concentration of NiCl2, as well as on the amino acid.

Assay of synovial fluid hyaluronic acid using high-performance liquid chromatography of hyaluronidase digests.

A high-performance liquid chromatographic method for the determination of hyaluronic acid levels in synovial fluids has been developed. The hyaluronidase sample digests, containing an internal standard (benzoic acid), were separated on a reversed-phase octadecylsilyl column eluted with 0.01 M tetrabutylammonium phosphate-acetonitrile (83:17, v/v) at pH 7.35. The determination was made on 1:10 diluted samples, by using a calibration curve from 50 to 500 micrograms/ml of human umbilical cord hyaluronic acid. For validation, the synovial fluids were simultaneously analysed by this method and a radiometric method: a high correlation was found between the two (correlation coefficient 0.94). The proposed method can be used to determine specifically the high hyaluronic acid levels of synovial fluids without interferences from other glycosaminoglycans or non-steroidal anti-inflammatory drug treatment.

Assessment of the developmental toxicity, metabolism, and placental transfer of N,N-dimethylformamide administered to pregnant rats.

This study evaluates the developmental toxicity and placental and milk transfer of N,N-dimethylformamide (DMF) in rats. Sprague-Dawley rats were given 0, 50, 100, 200, and 300 mg DMF/kg/day, by gavage, on Gestational Days (GD) 6 through 20. Maternal toxicity was indicated by depressions in weight gain and food consumption at doses >/=100 mg/kg. Fetal toxicity was indicated by decreased fetal body weight at doses >/=100 mg/kg, and by increased incidences of two skeletal variations (absent or poorly ossified supraoccipital and sternebrae) at 200 and 300 mg/kg. Thus, the maternal and developmental no-observed-adverse-effect level was 50 mg/kg/day. The time course disposition of [14C]DMF was examined over a 48-hr period in GD12- and GD18-pregnant rats after a single oral dose of 100 mg [14C]DMF/kg. Peak concentrations of radiocarbon occurred within 1 hr after dosing. Embryonic (GD12) and fetal (GD18) tissues accounted for 0.15 and 6% of the administered dose, respectively. Levels of radiocarbon in embryonic and fetal tissues were equal or slightly less than in maternal plasma up to 8 and 24 hr, respectively, and higher thereafter. HPLC analysis performed at intervals from 1 to 8 hr on GD12 and 1-24 hr on GD18 indicated that unchanged DMF and metabolites were readily transferred to the embryonic and fetal tissues, where their levels were generally equal to those in maternal plasma. The parent compound accounted for most of the radioactivity until 4-8 hr and then decreased. N-Hydroxymethyl-N-methylformamide (HMMF) and N-methylformamide (NMF) were the predominent metabolites and increased with time. Much lower concentrations were found for formamide and N-acetyl-S-(N-methylcarbamoyl)cysteine. Transfer of radioactivity into milk was studied in dams given a single oral administration of 100 mg [14C]DMF on Lactation Day 14. DMF, HMMF, and NMF were found in the milk at concentrations equal to those in plasma.