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Biomedical subjects

A R Singh

Publications and source records attributed to A R Singh.

6 recordsLinked to original sources
PubMed1976

Carcinogenic activity of a chlorinated polyether polyurethan.

On the basis of the results of an earlier study, a particular polyurethan sample (Y-238) was selected for further evaluation of its carcinogenic potential. This sample was subjected to physical and chemical tests for elucidation of its chemical structure, molecular weight, and molecular weight distribution. Additional biological tests were conducted on male NBR rats by implanting various quantities of the sample i.p., while others received an intrabronchus implant. Tumors, assessed histologically as malignant, were observed following both routes of implantation. The most common neoplasms of the pulmonary site was epidermoid carcinoma, while fibrosarcoma was the most common neoplasm in the peritoneal cavity. Data from the i.p. implantation suggested a dose-related incidence of cancers.

Animals↗
PubMed1975

Maternal-fetal transfer of 14C-di-2-ethylhexyl phthalate and 14C-diethyl phthalate in rats.

14C-Di-2-ethylhexyl and 14C-diethyl phthalates were administered intraperitoneally to pregnant rats on either Day 5 or 10 of gestation. Rats were sacrificed at 24-hr intervals starting on Days 8 and 11, respectively; maternal blood, fetal tissue, amniotic fluid, and placentas (whenever possible) were obtained. The 14C-activity of each sample was determined by scintillation counting. It was found that both diesters and/or their metabolic products were present in each of these compartments throughout the gestation period, thus suggesting that the embryo-fetal toxicity and teratogenesis reported previously could be the results of a direct effect of the compound (or its metabolites) upon developing embryonic tissue. Additionally, the reduction in concentration of 14C from these tissues as a function of time was found to fit a first-order excretion curve. From this model curve, the half-life for both compounds was calculated; the average was about 2.33 days for di-2-ethylhexyl phthalate and 2.22 days for diethyl phthalate.

Amniotic Fluid↗
PubMed1975

Carcinogenesis from polyurethans.

Seventeen polyurethans, containing various substituent groups, and a polyethylene were implanted i.p. in groups of male black Bethesda rats and were evaluated for carcinogenesis over a 2-year period. Thirteen of the polyurethans and the polyethylene were similarly studied in females. Tumor development in these animals was expressed in terms of the incidence in the at-risk population, and the tumorigenic latent period was approximated for each sample. Twenty months after implantation, the relative tumorigenicity (area under the corrected cumulative tumor mortality versus time curve) in the males ranged from 0 (for the unimplanted controls) to 6.18 (for Y-238); for female rats this range was 0.29 (for unimplanted controls) to 5.72 (for Y-238). Estimated latent periods in the males ranged from 5 months (for Y-304) to 16 months (for Y-303), and 22.5 months for the unimplanted controls; for the females, the range was from 9 months (for Y-290) to 13.5 months (for Y-217), and 14 months for the unimplanted controls. The relative tumorigenicity of each sample was also compared to its in vitro activation energy for thermal decomposition. These data are discussed in terms of solid-state versus chemical carcinogenesis.

Animals↗