Inhibitory effect of tetrachloro-p-hydroquinone and other metabolites of hexachlorobenzene on hepatic uroporphyrinogen decarboxylase activity with reference to the role of glutathione.

Exposure of rats to HCB caused a dose-dependent depletion of GSH. Chlorophenolic and sulfur-containing metabolites of HCB incubated with GSH-free rat liver cytosolic protein drastically diminished the UROD activity. In addition, HCB also exhibited inhibitory potency. The most effective compounds studied were TCH and its oxidation product, chloranil. Incubation of liver cytosolic protein and of GSH with HCB and its metabolites yielded results that suggested interaction between the compounds and cell constituents--an interaction that may cause inhibition of the hepatic UROD activity in the HCB-exposed organism.

Elimination of porphyrins and their precursors in rats pretreated with hexabromobenzene.

The elimination times of porphyrins and their precursors and of hexabromobenzene (HBB) itself were studied in female rats given 15 mg HBB by stomach tube every other day for 4 months. The concentrations of HBB in the blood, liver and adipose tissue were in the ratio 1:1.5:25, 24 hr after the last dose. Two weeks after the end of treatment, HBB was no longer detectable in the tissues. In animals given a single oral dose of 16.6 mg HBB/kg body weight, HBB was no longer detectable in adipose tissue 12 days after dosing. The half-life of HBB in adipose tissue was about 2.5 days in the animals given HBB for 4 months, and at the end of the treatment the concentrations of porphyrin in the liver, urine and faeces were increased to about 1000, 600-700 and 60-70 times the control values. The amounts of delta-aminolaevulinic acid and porphobilinogen in the urine of treated animals were 6-7 times those in controls. After the end of HBB treatment, it took almost 1.5 yr for delta-aminolaevulinic acid and porphobilinogen excretion to return to normal. Nearly 2 yr were needed for complete elimination of the accumulated liver porphyrins.

Excretion of metabolites of hexachlorobenzene in the rat and in man.

From the urine of rats treated with hexachlorobenzene (HCB), 21 metabolites were separated by capillary gas chromatography. Sulfur-containing metabolites were present in larger numbers and greater amounts than phenolic compounds. In studies on the origin of pentachlorophenol in man, HCB was determined in adipose tissue and pentachlorophenol in urine, and in 48 out of 60 females, 80-90% of the daily urinary pentachlorophenol appeared to be formed from HCB.

Metabolic fate of hexabromobenzene in rats.

To study the metabolic fate of hexabromobenzene (HBB) in female rats, the substance was administered in oral doses of 16.6 mg/kg body weight every other day for 2 weeks and the animals' excreta were examined for metabolites. Unchanged HBB, pentabromobenzene, oxygen- and sulphur-containing metabolites were detected in feces and urine. The sulphur-containing substances contained free mercapto groups except for the presence in feces of a methylmercapto derivative. The amount of sulphur-containing metabolites was estimated to be 15 times greater than that of oxygen-containing compounds. The relative proportions of the unchanged compound and its metabolites in the excreta were about 1:4.

Enteral absorption and biotransformation of the food additive octyl gallate in the rat.

Following oral administration of 14C-labelled octyl gallate in a single dose of 15 mg/kg to female rats, only 20-30% of the radioactivity administered was detected in the tissues, while 60-80% of the dose was found in the contents of the gastro-intestinal tract up to 12 hr after administration. Isotope dilution analysis demonstrated the presence of the unchanged ester in the tissues. In the liver, the highest concentration of the ester demonstrated was 1.6 micrograms/g. in a rat killed 10 min after treatment. In the 24 hr following ip administration of labelled octyl gallate, about 91% of the administered radioactivity was recovered. Most of this was in the form of metabolites, only 9% being accounted for as unchanged ester.

Steric factors in the pharmacokinetics of lindane and alpha-hexachlorocyclohexane in rats.

1. The elimination of alpha-1,2,3,4,5,6-hexachlorocyclohexane (alpha-HCH) by rats, as assessed by g.l.c. determination of the chemical's disappearance from depot fat, exhibited a sex difference (males:females = 4:1) and a sizeable deuterium isotope effect (6.3 in males). 2. Lindane (gamma-HCH), by contrast, disappeared from depot fat, skeletal muscle, brain and blood at nearly the same rates in both sexes. Perdeuteration, though effective in reducing hepatic removal, did not significantly retard the overall elimination of this isomer (isotope effect in males less than 2). Partial explanation of this finding is that lindane and lindane-d6 are equally subject to dechlorination in the gut. 3. alpha-HCH distributed into cerebral white matter in preference to grey matter to a much higher degree than did lindane and the beta-isomer of HCH, and elimination from that tissue was slow. The finding is considered to indicate a stereoselective affinity of alpha-HCH to some component(s) of myelin.

Rat liver alterations after chronic treatment with hexachlorobenzene.

Groups of female rats were treated orally with 0.5, 2.0, 8.0, and 32 mg/kg hexachlorobenzene twice a week for 203 days. The liver content of hexachlorobenzene was found to be dose-dependent. In the animals treated with the highest dose the concentration was 273 mug/g hexachlorobenzene. In the fresh and fixed hepatic tissue of the treated animals pink fluorescence was observed. Electron microscopy revealed a dose dependent enlargement of all hepatocytes due to proliferation of the SER in the centrolobular area or to increased glycogen deposits (beta- or alpha-particles) and SER in the intermediary and periportal area. Numerous porphyrin deposits and siderosomes, intimate disorganisation and moderate dislocation of the RER and a moderate enlargement of bizarre-sharped mitochondria were recognized. The relationship between porphyrin crystals and mitochondria on the one hand and between SER and glycogen deposits on the other is discussed.

Studies on the toxicology of hexachlorobenzene. IV. Sulphur-containing metabolites.

After administration of hexachlorobenzene rats excrete sulphur-containing conjugates from which pentachlorothiophenol can be split off. In the present study we describe the identification of pentachlorothiophenol and pentachlorothioanisol in the livers of animals treated with hexachlorobenzene. In order to clarify the further fate of these two substances, we administered them to rats, and isolated the conversion products excreted in the urine and feces. The metabolites of pentachlorothiophenol and pentachlorothioanisol are excreted in both conjugated and free form. From extracts of the excreta, we isolated tetra- and trichlorobenzene with two or three sulphur-containing substituents on the ring, analogous compounds in which thiol groups were converted into sulphoxide and sulphone groups, as well as analogous compounds with a phenolic oxygen in addition to sulphur, and sulphur-containing compounds in which clorine was replaced by hydrogen. Following administration of the sulphoxide and of the sulphone of pentachlorothioanisol under analogous conditions, pentachlorothiophenol and pentachlorothioanisol and their metabolites were detected in the excreta of the animals. No evidence was obtained that the parent compounds are excreted in the unchanged form.

Effect of hypophysectomy on the stimulation of liver growth by alpha-hexachlorocyclohexane, phenobarbital, and partial hepatectomy in the rat.

alpha-Hexachlorocyclohexane (alpha-HCH) or phenobarbital (PB) elicit growth and cell multiplication in rat liver. In hypophysectomized rats, alpha-HCH and PB induce an increase in liver mass, but no increase in liver DNA. Hypophysectomy without additional treatment results in a decrease of liver size and RNA, while the DNA content remains unchanged, thereby leading to a relative DNA surplus. 1/3-hepatectomy in hypophysectomized animals leads to a small increase of hepatic DNA only; after 2/3-hepatectomy 75-80% of the original liver DNA are restored. In rats with intact hypophysis losses of liver DNA are known to be restored completely. The findings suggest that the relative DNA surplus in hypophysectomized rats prevents the stimulation of DNA synthesis by weak growth stimuli such as alpha-HCH, PB, and 1/3-hepatectomy. If the relative DNA surplus is eliminated by partial hepatectomy, the inducers do produce DNA multiplication. It is concluded that the induction of liver growth and cell multiplication by alpha-HCH and PB does not require the presence of the hypophysis or one of its hormones.

Studies on the toxicology of hexachlorobenzene. II. Identification and determination of metabolites.

Female rats were dosed intraperitoneally with 14C-hexaxhlorobenzene. The drug was administered on 2 or 3 occasions. The total doses amounted to 260 and 390 mg/kg 14C-hexachlorobenzene, respectively. Urine and feces from the animals were collected over a period of 4 weeks after the first injection. Both excreta and some tissues of the animals were examined for their content of radioactivity and for hexachlorobenzene and its metabolites. Gas chromatography, isotope dilution analysis, and combined gas chromatography-mass spectrometry were used to identify the metabolites of hexachlorobenzene. In urine pentachlorophenol, tetrachlorohydroquinone, and pentachlorothiophenol were present as major metabolites. One of the isomers of tetrachlorothiophenol was present as a minor metabolite. In the feces pentachlorophenol and pentachlorothiophenol only were identified. At the end of the experiment, carbon-14 excreted with urine and feces amounted to 7% and 27%, respectively, of the radioactivity administered. More than 90% of carbon-14 excreted in urine was contained in the major metabolites. In the feces about 30% of the excreted radioactivity was bound to metabolites and about 70% was contained in the unchanged drug, while in the tissues of the animals only pentachlorophenol was detected in measurable amounts, accounting for 10% of label in blood and less than 0.1% of carbon-14 determined in body fat. Total radioactivity contained in the metabolites detected in the animal body and in the excreta at the end of the experiment accounted for about 16% of the administered radioactivity.

Studies on the toxicology of hexachlorobenzene. I. Pharmacokinetics.

In female rats dosed orally with 14C-hexachlorobenzene the extent of intestinal absorption of carbon-14 has been found to be dependent on the form of application. When the substance was given as a solution in oil about 80% of the dose administered was absorbed, but when given as an aqueous suspension only 6%. In animals treated with 14C-hexachlorobenzene dissolved in oil, all tissues contained radioactivity. Highest levels were found in adipose tissue, lowest in blood and muscle. Peak values of radioactivity were reached between 2 to 5 days after application. Elimination was studied after intraperitoneal application of 4 mg/kg14C-hexachlorobenzene dissolved in oil. Two weeks after administration, 34% of the radioactivity administered was recovered in the feces and 5% in urine. About 80% of carbon-14 excreted in feces and about 4% in urine was contained in the unchanged drug. This indicates that biodegradation of hexachlorobenzene in the rat is not insignificant. No radioactivity was detected in the expired air.