Mitsuru Shimizu

Effects of fasting on cadmium toxicity, glutathione metabolism, and metallothionein synthesis in rats.

Acute oral toxicity of Cd (as cadmium chloride) was enhanced in rats fasted 24 hr, as shown by a markedly decreased LD50. To examine the relationship among Cd toxicity, hepatic glutathione (GSH), and metallothionein (MT) during fasting, rats were administered 75 mg Cd/kg orally 24 hr after fasting and euthanized after a further 4 or 24 hr for various assays. Serum glutamic-pyruvic transaminase activity 24 hr after Cd treatment was higher in fasted rats than in fed rats. Both total GSH and nonprotein sulfhydryl (NPSH) concentrations in liver decreased to 50% of control levels after 28 hr of fasting and returned to 75% of control values by 48 hr. Total hepatic GSH concentration in fed rats decreased 4 and 24 hr after Cd treatment, whereas that in fasted rats remained unchanged at 4 hr and decreased significantly at 24 hr. Cd uptake by the liver (both concentration and content) 24 hr after Cd treatment was higher in fasted rats than in fed rats. Hepatic MT concentration was markedly increased by Cd treatment and higher in fasted rats than in fed rats. There was no relationship between Cd toxicity and hepatic thiobarbituric acid (TBA) value, an indicator of lipid peroxidation. Fasting had no effect on hepatic GSH peroxidase and GSH reductase activities. These enzymes probably are not involved in Cd toxicity. On histological examination, focal degenerative and necrotic changes were observed from the midlobular to the pericentral region in the livers of fed rats 24 hr after Cd treatment. These changes were enhanced by fasting, diffusing from the pericentral to the periportal region. Histochemical examination revealed a heterogeneous distribution of GSH in the livers of fed rats, with strong staining of GSH in the periportal region. This heterogeneous distribution of GSH in liver was not observed in fed rats 4 hr after Cd treatment or in fasted rats at 24 hr. The present results suggest that hepatic GSH plays an important role in protection against Cd toxicity before the onset of MT synthesis. Animals in bad condition, such as that resulting from interruption of nutrient supply, cannot be protected against Cd toxicity even if the hepatic MT level is high.

Comparative teratogenicity of Di-n-butyltin diacetate with n-butyltin trichloride in rats

Teratological tests were conducted on di-n-butyltin diacetate (DBTA), and n-butyltin trichloride (MBTC). Pregnant Wistar rats were treated orally with DBTA at doses of 0, 1.7, 5.0, 10.0, and 15.0 mg/kg/day or with MBTC at doses of 0, 50, 100, 200, and 400 mg/kg/day during days 7–17 of gestation. Cesarean sections were performed on day 20 of gestation. Thymic atrophy of the pregnant rats was observed in a dose-dependent manner by DBTA treatment. The incidence of dead or resorbed fetuses and total resorption fetuses increased at the highest dose of DBTA. The incidence of fetuses with external malformations, such as cleft mandible, cleft lower lip, ankyloglossia (tongue-tie) and schistoglossia (cleft tongue), increased in a dose-dependent manner by DBTA treatment. The incidence of fetuses with skeletal malformations such as anomaly of mandibular fixation, fused ribs, fused cervical vertebral arches and fused thoracic vertebral arches also increased at 10.0 and 15.0 mg/kg. However, MBTC, one of the main metabolites of di-n-butyltin, failed to show any evidence of teratogenic activity at any doses tested. The results indicate that DBTA has potent teratogenic effects on rat fetuses, and DBTA is different from MBTC with respect to teratogenic effects.

Effects of feeding and fasting on hepatolobular distribution of glutathione and cadmium-induced hepatotoxicity.

Relationship between hepatolobular distribution profile of glutathione (GSH) and cadmium (Cd)-induced hepatotoxicity was examined in both fed and fasted rats by computerized densitometry of histochemically stained GSH in the liver sections using an image analyzer system. In fed rats, density gradient distribution of hepatolobular GSH, which was higher in the periportal region than in the perivenous one, was always observed even at a diurnally minimal concentration of GSH. This heterogeneous distribution of GSH, however, disappeared in fasted rats, even though the hepatic GSH concentration recovered to 81% of the control level in rats fasted for 48 h. In histopathological examination on livers 24 h after oral treatment of fed and fasted rats with 60 mg Cd/kg, zonal necrotic changes were observed from the perivenous to midlobular region but not in the periportal one in fed rats even at a diurnally minimal concentration of hepatic GSH. On the other hand, necrotic changes in the liver extended to the panlobular region including the periportal one in fasted rats. These necrotic changes were greater with a longer duration of fasting. These results suggest that the density gradient distribution of hepatic GSH but not the actual concentration of the compound plays an important role in protecting rats against acute hepatotoxicity of Cd.

Effects of diethylene glycol monomethyl ether on pregnancy and postnatal development in rats

The effects of oral treatment of Wistar rats with diethylene glycol monomethyl ether (diEGME) were examined. In a preliminary dose-finding study with non-pregnant rats, diEGME treatment at doses up to 4,000 mg/kg/day on 11 consecutive days decreased relative weights of thymus and pituitary gland, white and red blood cell counts, hemoglobin concentrations and hematocrit levels. In pregnant rats, treatment at doses of >3,000 mg/kg/day (over gestation days 7–17) caused total resorption of all litters. In teratology and postnatal studies, pregnant rats were treated with diEGME at doses of 0, 200, 600, and 1,800 mg/kg/day from day 7 through 17 of gestation. At 200 mg/kg, there were no adverse effects on either dams, fetuses, or neonates. At 600 mg/kg, dams were not affected, but fetal body weights were decreased, and fetal thymus and ossification were adversely affected. At 1,800 mg/kg, maternal thymus weights and food consumption were decreased, and visceral malformations of the cardiovascular system were seen in 28.0% of the fetuses. Only 6.3% of the pups delivered by dams treated with 1,800 mg/kg of diEGME survived for 4 days after birth. Thus, diEGME was teratogenic in Wistar rats, but the spectrum differed from that in Sprague-Dawley rats. In addition to teratogenicity, diEGME had significant adverse effects on postnatal development. The most sensitive organ to diEGME was the thymus in both dams and fetuses.

Critical gestational day of teratogenesis by Di-n-butyltin diacetate in rats

There is growing concern about the biological effects of organotin compounds widely distributed in the environment. Despite the large amount of toxicological data, only recently have the teratological and embryolethal effects of organotins on mammals been reported with the limited chemical species, for example, tri-n-butyltin compounds (Davis et al. 1987; Itami et al. 1990; Noda et al. 1991a), di-n-butyltin compounds (Noda et al. 1988; Ema et al. 1990), and triphenyltin compounds (Schatzow 1985; Noda et al. 1991b). In our previous studies, we have demonstrated that external malformations (cleft mandible, cleft lower lip, ankyloglossia and schistoglossia) and/or skeletal malformations (fused ribs, fused cervical vertebral arches and fused thoracic vertebral arches) occurred in rat fetuses after maternal exposure to di-n-butyltin diacetate (DBTA) throughout gestation (Noda et al. 1988) and during the period of organogenesis (Noda et al. in press). Similar observations with di-n-butyltin dichloride have been reported by Ema et al. (1991).

Synthesis of regioisomeric dimethylbenzyl mercapturic acids anticipated from the metabolism of 1,2,3-trimethylbenzene

Abstract The synthesis of two regioisomeric mercapturic acids, N-acetyl-S-(2,3-dimethylbenzyl) -L-cysteine and N-acetyl-S-(2,6-dimethylbenzyl)-L-cysteine, was undertaken to investigate the operation of mercapturic acid pathway in the metabolism of 1,2,3-trimethylbenzene. The method applied was based on that we described recently in the synthesis of mercapturic acids derived from m- and p-xylenes.