Effects of inhalation exposures to an M1-receptor agonist on ventilation in rhesus monkeys.

Information was needed on effects of possible occupational inhalation exposure to an M1-receptor agonist (xanomeline) such as might occur during the manufacturing process. Both acute and repeated inhalation exposures to xanomeline were carried out in six male rhesus monkeys using a head-dome exposure system. Exposure concentrations ranged from 0.3 to 10 mg/m3. The exposure durations were up to 2 weeks. Decreases in tidal volume and increases in respiratory frequency were both time and concentration related during acute exposures. These effects were blocked with atropine pre-treatment. Correlation with pulmonary resistance measurements in two monkeys suggested that these were bronchoconstrictive changes that increased with severity with time at a given concentration and with concentration when measured after a constant exposure time. The dose-response was relatively steep with 10 mg/m3 becoming intolerable to the monkeys after approximately 15 minutes, but no measurable effects were observed at 0.3 mg/m3 after up to 4 hours of exposure. To investigate the effects of repeated exposures, monkeys were exposed for 4 hr/day, 5 days/wk for 2 weeks to 0.0 (air only), 0.3, and 1.2 mg xanomeline/m3 of air. When compared to the air-only exposure, 0.3 mg/m3 caused no significant changes in tidal volume. In contrast, 1.2 mg/m3 caused a rapid and significant decrease in tidal volume that was sustained throughout the 4-hr exposure. A slower rise in breathing frequency also occurred. Repeated exposures did not alter the effects seen after a single exposure. It is concluded that xanomeline, a M1-receptor agonist, can acutely alter normal ventilation in non-human primates at airborne concentrations > or = 0.6 mg/m3 and should be carefully controlled in a manufacturing environment. The no-observed-effect concentration was 0.3 mg/m3.

Stereoselective disposition of the enantiomers of the benzoquinolinone LY191704, a human type I 5 alpha-reductase inhibitor. Differences between rats and dogs.

The benzoquinolinone LY191704, a potent and selective human type I 5 alpha-reductase inhibitor, is a racemic mixture of the compounds LY300502 and LY300503. Rats were treated orally with 10, 30, or 100 mg of LY191704/kg/day for 1 month. Plasma concentrations of LY191704 increased with dose. Both the AUC and maximal concentration values were reduced at 30 and 100 mg/kg on the last day, compared with the first day of treatment. In rat plasma the ratio of LY300502 to LY300503 ranged from 1.6 to 2.0 after the first dose and from 1.6 to 2.4 after the last dose. In dogs administered the same daily oral doses of LY191704 for 1 month, the plasma ratio of LY300502 to LY300503 was essentially unity at the beginning and end of the study. After daily oral administration of LY300502 or LY300503 to rats, at 30, 100, or 300 mg/kg for 14 days, the mean dose-normalized AUC value for LY300503 was 56% of that for LY300502 after the first dose and 38% after the last dose. The rate of metabolic oxidation for LY300502 in rat liver microsomes was approximately 32% of that for LY300503, whereas no differences were observed in the metabolism of the enantiomers in dog liver microsomes. The differences observed between LY300502 and LY300503 were attributed to preferential metabolism of LY300503 in rats. The data indicated that LY300503 was subject to a greater rate of metabolism than LY300502 and induced its own metabolism in rats and that the preferential metabolism of LY300503 was species-specific.

A convenient method for the determination of hepatic lauric acid omega-oxidation based on solvent partition.

Assessment of hepatic omega-oxidation of fatty acids by cytochrome P450IV enzymes in toxicology studies can be a means of evaluating test compound effects on peroxisomal proliferation. Routine assay of omega-oxidation, however, requires a simpler method of enzymatic analysis than currently described GC, TLC, or HPLC methods. A method depending upon selective solvent separation of radiolabeled lauric acid from radiolabeled 11- or 12-hydroxydodecanoic acid has been developed. Following enzymatic incubation and addition of 15% methanol to the acidified postincubation mixtures, partitioning with an alkane solvent such as iso-octane, cyclohexane, or n-hexane separated the lauric acid and the hydroxylated products into two immiscible phases. Approximately 97% of the substrate partitioned into the organic phase, and approximately 84% of the hydroxylated products partitioned into the aqueous phase. Subsequent quantitation of the enzymatic activity required only liquid scintillation counting of the aqueous phase. Hepatic homogenates from male rats treated with 0.01, 0.05, 0.125, and 0.25% clofibric acid in the diet for 7 days had enzyme levels 1.3, 6.1, 11.1, or 15.9 times control values, respectively, when assayed by a conventional TLC method, and 1.3, 5.3, 12.3, or 15.3 times control values when assayed by the solvent partition method. The data indicate that the partition method demonstrates comparable sensitivity and better precision and linearity than a more conventional TLC method when induction of hepatic microsomal enzymes in rats is studied.

Effects of chronic treatment with the leukotriene D4-antagonist compound LY171883 on B6C3F1 mice.

A 2-year toxicity/oncogenicity study was done to evaluate the potential effects of the leukotriene antagonist LY171883 in B6C3F1 mice. Dietary concentrations of LY171883 during the initial 7 months of the study were 0.0, 0.005, 0.015, or 0.05% but were increased to 0.0, 0.0075, 0.0225, or 0.075% during Months 7 through 24. The estimated average daily compound intake was 0.0, 7.3, 22.5, or 80.5 mg/kg for males and 0.0, 9.2, 27.5, or 95.9 mg/kg for females. Survival was not adversely affected by treatment, however, body weight of males and females in the high dose group was significantly lower than that of controls. The chronic toxicity was localized primarily to the liver. Liver weights were increased in males in the high dose group and in females in the mid and high dose groups. Microsomal p-nitroanisole-O-demethylase activity was increased in mid and high dose females. Hepatic peroxisomal beta-oxidation was increased approximately twofold in both sexes in the high dose group only. Centrilobular eosinophilic granular change of hepatocytes was a common histopathologic finding in male and female mice in the high dose group, with the incidence and severity being greater in females. An increased incidence of hepatocellular carcinomas was observed in female mice in the mid and high dose groups. The number of male mice in the high dose group with hepatocellular carcinomas was higher than that of controls but the change was not statistically significant. Hepatocellular adenomas were increased in females in the high dose group but not in males. All groups of treated females had increased nodular hepatocellular hyperplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

The toxicity and mechanism of action of bromethalin: a new single-feeding rodenticide.

Bromethalin is a new rodenticide for the control of commensal rodents. Doses in excess of the LD50 (2 mg/kg in rats) will cause death within 8-12 hr and it is preceded by one to three episodes of clonic convulsions with death usually due to respiratory arrest. Multiple low doses or sublethal intoxication yields hind leg weakness and loss of tactile sensation in rodents. Histopathology of the brain and spinal cord of these animals revealed a spongy degeneration of the white matter which was shown upon ultramicroscopic examination to be intramyelenic edema. No inflammation or cellular destruction of neuronal tissue was noted. LD50 values ranged from 1.8 mg/kg in the cat to approximately 13 mg/kg in rabbits. The only apparent nonsusceptible species was the guinea pig which could tolerate doses in excess of 1000 mg/kg without effect. Identification of the desmethyl metabolite was demonstrated in the blood and liver of treated animals by comparison of chromatographic retention times to that of a reference standard, but direct mass spectral identification was unsuccessful in part due to the low dose which could be administered. Therefore, the metabolism of bromethalin was studied by indirect means. Animals were pretreated with three inducers of microsomal drug metabolism: phenobarbital, 3-methylcholanthrene (3MC), and Aroclor 1254 (Aroclor) and one inhibitor, SKF-525A. Pretreated mice or rats were given an LD50 dose of bromethalin or the desmethyl analog and the percentage of surviving animals was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Coupled beta-cyclodextrin and reverse-phase high-performance liquid chromatography for assessing biphenyl hydroxylase activity in hepatic 9000g supernatant.

Coupled beta-cyclodextrin bonded-phase and reverse-phase high-performance liquid chromatography with fluorescence detection has been employed to detect the major hydroxylated metabolites of biphenyl following in vitro incubation with hepatic 9000g supernatant. The method requires only 0.3 mg of protein and its sensitivity was as low as 0.36 nmol metabolite formed/mg protein/h (0.32 pmol injected) for 2-, 3-, and 4-hydroxybiphenyl. Microsomes need not be purified and no organic extraction or derivatization was required. The method was employed successfully with samples from rats and mice treated with Aroclor, beta-naphthoflavone, or phenobarbital; from monkeys dosed with Aroclor; and from untreated dogs.

Characterization of liver enlargement induced by compound LY171883 in rats.

Compound LY171883 caused dose-related and reversible hepatomegaly in male Fischer 344 rats. Histological examination revealed hepatocellular hypertrophy with no other evidence of liver disease. There were only minor changes in serum glucose, total bilirubin, alkaline phosphatase, and alanine transaminase which were generally unrelated to dose and dissociable from the hepatomegaly. Total liver DNA increased but the DNA concentration decreased, indicating that liver growth involved a combination of hypertrophy and hyperplasia. Total liver protein and RNA increased. Hepatic mitochondrial protein content increased but cytochrome oxidase activity was not changed. There were minor changes in mitochondrial respiratory parameters; however, all the values were in the normal range and there was no indication of mitochondrial toxicity. Microsomal protein, drug-metabolizing activity, and cytochrome P-450 increased, but glucose-6-phosphatase activity was not changed. The induction of drug-metabolizing enzymes and absence of toxicity were evidence that the hepatomegaly was an adaptation to an increased functional load in the liver. An increase in catalase activity suggested that the response may have also involved peroxisomes. In addition to rats, LY171883 administration caused hepatomegaly in mice and hamsters at daily exposures exceeding 100 mg/kg. The response was not observed in guinea pigs, beagle dogs, or rhesus monkeys given maximum tolerated doses, indicating LY171883-induced hepatomegaly is not a response common to all species. The doses required to elicit hepatomegaly greatly exceeded doses that produce pharmacological efficacy in animals and those that are expected to be used clinically. Since humans will not receive doses comparable to those given rodents, and considering that the primate species tested did not experience hepatomegaly, it is unlikely that the effect observed in rodents can be extrapolated to humans.