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Biomedical subjects

B K Leong

Publications and source records attributed to B K Leong.

At least 19 recordsLinked to original sources
PubMed1987

Retinopathy from inhaling 4,4'-methylenedianiline aerosols.

4,4'-Methylenedianiline (MDA) is an important chemical intermediate in the production of isocyanates and polyurethane elastomers and polymers. The health hazards from acute inhalation exposure to the aerosols were evaluated. Guinea pigs of albino and pigmented strains were exposed nose-only to the aerosols of MDA in polyethylene glycol 200 (PEG) solution. The exposure was 4 hr per day, 5 days per week for a total of 10 exposures in 2 weeks. The time-weighted average aerosol concentration was 0.44 +/- 0.09 mg/liter and the optical number length mean diameter of the aerosol particle was 2.4 micron with sigma g of 2.1. During exposures, no overt respiratory distress was observed. Two weeks after the exposures, the guinea pigs were tested for possible dermal sensitization by being challenged with dermal application of MDA-PEG solutions at concentrations of 0, 2, 20, and 200 mg/ml. Neither dermal irritation nor allergic response was detected under this experimental condition. Thereafter, the animals were tracheostomized for measurements of changes in lung insufflation pressure for detecting possible changes in the distensibility of the lungs from a challenge dose of an aerosol of MDA-PEG at a concentration of 200 mg/ml. No significant changes were observed under this testing condition. Finally, the animals were euthanized for histopathologic examinations of eye, lung, liver, and kidney. The most remarkable findings was the degeneration of the inner and outer segments of the photoreceptor cells and the pigmented epithelial cell layer of the retinas of both albino and pigmented strains of guinea pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1983

Enhanced bronchoconstriction responses to prostaglandin F2 alpha following inhalation of sulfur dioxide.

The effect of chronic sulfur dioxide (SO2) inhalation was investigated in pharmacologic-induced bronchoconstriction in beagle dogs. Increases in pulmonary resistance (RL) and decreases in dynamic lung compliance (CDYN) were observed with i.v. and aerosol administration of prostaglandin F2 alpha (PGF2 alpha). After control historical data were accumulated, the animals received exposures of 500 ppm of SO2 for two hours twice a week. After six months of chronic SO2 exposure, a significant enhancement in the RL response to i.v. and aerosolized PGF2 alpha was observed as compared to pre-SO2 data. Tracheobronchial inflammation, as observed by fiberoptic bronchoscopy, occurred as a result of the chronic inhalation of SO2; however, only a small increase in mucous production was observed visually. In addition, hypercapnic and acidotic changes in blood gas profiles were found. Therefore, beagle dogs chronically exposed to SO2, developed hyperactive airways as seen by increased sensitivity to PGF2 alpha. This model appears to reflect many of those changes observed in clinical bronchial hyperreactivity and may provide an additional insight into obstructive airways disease.

Animals↗
PubMed1981

Subchronic toxicity study of 1,2,4-trichlorobenzene in the rat, rabbit and beagle dog.

Male rats, rabbits and dogs were exposed to 0, 30 or 100 ppm of 1,2,4-trichlorobenzene (TCB) for 7 hours/day, 5 day/week for 30 exposures in 44 days. In all 3 species, there were no significant effects on body weight gain, hematologic and serum biochemical tests or gross and histopathologic appearance of tissues. At 100 ppm TCB, both rats and dogs had increased liver weights, and the rats also had increased relative kidney weight at this higher exposure level. Urinary excretion of porphyrins were increased in rats exposed to 30 or 100 ppm TCB, most likely as a result of hepatic induction by TCB. In view of the reversibility of this porphyrin induction noted in a companion study, and the absence of other indications of discernible toxicity, this increased urinary excretion of porphyrins is best considered more of a compound-specific physiologic effect rather than a toxic effect.

Air↗
PubMed1979

Teratogenic potential of inhaled carbon monoxide in mice and rabbits.

Pregnant CF-1 mice and New Zealand rabbits were exposed to carbon monoxide at a concentration of 250 ppm for 7 or 24 hours daily during the period of major organogenesis, days 6 through 15 of gestation in mice and 6 through 18 of gestation in rabbits. Carboxyhemoglobin levels in the range of 10--15% were observed in both species (control animals had 0.7% or less). Carbon monoxide was not found to be teratogenic in either species. In mice, a significant increase in the incidence of some minor skeletal variants was observed. One litter in each of the carbon monoxide-exposed groups of mice was completely resorbed; none of the litters of control mice or of control or exposed rabbits were completely resorbed. The fetuses of mice exposed to carbon monoxide for seven hours daily were heavier than control fetuses, and those exposed for 24 hours daily were lighter than control fetuses. The reason for this result is not known.

Abnormalities, Drug-Induced↗
PubMed1979

Teratogenic potential of dichlorvos given by inhalation and gavage to mice and rabbits.

Dichlorvos (2,2-dichlorovinyl dimethyl phosphate) is an important organophosphate insecticide and anthelmintic with widespread use. The purpose of this study was to evaluate the teratogenic potential of dichlorvos given orally at the maximum tolerated dose to mice (60 mg/kg/day) and rabbits (5 mg/kg/day) and by inhalation in both species at a concentration of 4 microgram/l seven hours daily. Dichlorvos was not found to be teratogenic in either species by either route of administration.

Administration, Oral↗
PubMed1978

Induction of pulmonary carcinoma in rats by chronic inhalation of dust from pulverized asbestos pipe covering.

Rats and hamsters were exposed to the dust of pulverized asbestos pipe covering at an average concentration of 85 mg/m(3) for 6 h/d, 5 d/wk, for 7 mo, followed by a lifetime observation period. In rats, the pulmonary responses were alveolar adenomatous proliferation, nonprogressive fibrosis, squamous metaplasia, and a substantial incidence of pulmonary carcinoma formation. A smaller group of hamsters exposed under these conditions experienced an earlier onset of mortality than control hamsters, which were not subjected to the exposure regimen. Although this prevented conclusive evaluation of the pulmonary response in this species, no pulmonary neoplasms were noted in the surviving hamsters.

Animals↗