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Biomedical subjects

J R Meeks

Publications and source records attributed to J R Meeks.

10 recordsLinked to original sources
PubMed1993

The Comprehensive Health Organization--a practical solution for an integrated health care system.

This brief report takes a look at the structure and functions of a new type of health care delivery system, the comprehensive health organization (CHO). The development of such a system, however, requires a new mindset or shift of focus: none of the activities of a CHO has been part of the training or experience of providers in the Canadian health care system. The range of services a CHO would offer, whether they would be provided by the CHO or by an outside contractor, the possible risks involved, and who the potential participants would be are also discussed.

Comprehensive Health Care↗
PubMed1989

Health effects of the alkylbenzenes. II. Xylenes.

The alkylbenzenes are a class of six-membered ring aromatic compounds that have a variety of alkyl groups attached. These chemicals are liquids with relatively low boiling points used primarily as solvents or as starting materials in the synthesis of other chemicals and drugs. They are integral components of gasoline, distillate fuels and other petroleum products and are economically important in the chemical, petroleum, pharmaceutical, polymer, paint and dye industries. Alkylbenzenes such as toluene, the xylenes, ethylbenzene, styrene and cumene are produced and utilized in large quantities and therefore, present the possibility of exposure to humans and to wildlife. Fortunately, the toxicity of alkylbenzenes has been found to be rather low and therefore, the human and environmental risks are probably low. In modern industrial activities, exposures to the alkylbenzenes are minimized by workplace controls or personal protective equipment which meet guidelines for maximum allowable exposure concentrations that have been established for the workplace. Nevertheless, considerable quantities of alkylbenzenes are released to the environment each year through solvent and fuel evaporation, accidental spills and misuse, and considerable toxicological information for these materials has appeared in the recent literature. This present paper, the second in a series reviewing the potential health effects of alkylbenzenes, covers the toxicology and disposition of the dimethyl-substituted benzenes (the xylenes) in animals and man.

Animals↗
PubMed1989

Pharmacokinetics and metabolism of benzene in Zymbal gland and other key target tissues after oral administration in rats.

Solid tumors have been reported in the Zymbal gland, oral and nasal cavities, and mammary gland of Sprague-Dawley rats following chronic oral administration of benzene. The cause for the specificity of such lesions remains unclear, but it is possible that tissue-specific metabolism or pharmacokinetics of benzene is responsible. Metabolism and pharmacokinetic studies were carried out in our laboratory with 14C-benzene at oral doses of 0.15 to 500 mg/kg to ascertain tissue retention, metabolite profile, and elimination kinetics in target and nontarget organs and in blood. Findings from those studies indicate the following: a) the Zymbal gland is not a sink or a site of accumulation for benzene or its metabolites even after a single high dose (500 mg/kg) or after repeated oral administration; b) the metabolite profile is quantitatively different in target tissues (e.g., Zymbal gland, nasal cavity), nontarget tissues and blood; and (c) pharmacokinetic studies show that the elimination of radioactivity from the Zymbal gland is biphasic.

Administration, Oral↗
PubMed1988

Health effects of the alkylbenzenes. I. Toluene.

The alkylbenzenes, toluene being the most common example, represent a class of six-membered ring aromatic compounds that have a variety of alkyl groups attached. These chemicals are liquids with relatively low boiling points and are used primarily as solvents or as starting materials in the synthesis of other chemicals and drugs. They are also integral components of gasoline, distillate fuels and other petroleum products. These substituted aromatics are economically important in the chemical, petroleum, pharmaceutical, polymer, paint and dye industries. Alkylbenzenes such as toluene, xylene, ethylbenzene, styrene and cumene are toxicologically important since they are produced, used or disposed of in the largest quantities and therefore might pose significant and potential health risks to man and the environment. In general, the toxicity of alkylbenzenes has been found to be relatively low. Also, for the most part, human and environmental risks are low; however, there may be a few operations where the potential for high exposure could exist. These exposures are minimized by workplace controls or personal protective equipment. Furthermore, health risks for humans are minimized by guidelines for maximum allowable exposure concentrations which have been established for the workplace. This present paper reviews the toxicology and disposition of toluene in animals and humans.

Animals↗
PubMed1986

Systemic toxicity from subchronic dermal exposure, chemical characterization, and dermal penetration of catalytically cracked clarified slurry oil.

Clarified slurry oil (CSO), the heavy residual fraction from the fluidized catalytic cracker, was applied to the shaven backs of groups of 10 male and 10 female Sprague-Dawley rats 5 days/week for 13 weeks at doses of 8, 30, 125, or 500 mg/kg/day, and to another group for 2 weeks at doses of 2000 mg/kg/day. The rats were fitted with cardboard Elizabethan collars to minimize the ingestion of the test material, which was applied undiluted and remained uncovered on the skin. A similar group of rats served as controls; they were treated in the same manner except that no CSO was applied to their skin. There was a dose-related mortality and depression of body weight gain in the rats treated with CSO at doses of 30 mg/kg/day or greater; none of the rats dosed at 2000 mg/kg/day survived more than 2 weeks. The primary target organs of CSO toxicity were the liver, thymus, and bone marrow. The effects on the liver included increased weight (250% at 500 mg/kg/day), cholangiolitis, diffuse liver cell degeneration and hypertrophy, necrosis, fibrosis, decreased serum glucose, increased levels of alkaline phosphatase, aspartate aminotransferase, alanine amino transferase, bilirubin, and triglycerides. The thymus was found to be small and upon microscopic examination to be atrophic or hypoplastic. Erythroid hypoplasia was found in the bone marrow of some of the rats dosed at 30 mg/kg/day and increased in severity with increasing dose. The erythroid hypoplasia was accompanied by a dose-related anemia. Even in the rats dosed at 8 mg/kg/day, very slight abnormalities in the bile ducts were observed upon microscopic examination of the liver. Chromatographic separation and analyses demonstrated that CSO contains about 58% 3- to 5-ring polycyclic aromatic hydrocarbons (PAHs) and approximately 8-10% carbazole derivatives. In vitro and in vivo skin penetration studies demonstrated that the carbazole materials penetrate through the skin to a considerable extent (about 44%); less penetration was observed with 2- or 3-ring (8-13%) or 5-ring PAHs (3%).

Administration, Cutaneous↗
PubMed1983

Ion-pair reverse phase liquid chromatographic determination of sodium acifluorfen in feed.

Ion-pair reverse phase liquid chromatography (LC) and UV detection at 280 nm have been used to determine sodium acifluorfen (sodium-5-[2-chloro-4-(trifluoromethyl)-phenoxy]-2-nitrobenzoate), an experimental diphenyl ether herbicide, in dog feed. Sodium-5-(2,4-dichlorophenoxy)-2-nitrobenzoate is used as the internal standard. The feed is homogenized in 0.01N HCl, followed by ethyl acetate extraction, and centrifugation. The organic layer is removed and evaporated and the residue is reconstituted in methanol and filtered before LC analysis (mobile phase methanol-water (58 + 42), 0.005M in tetrabutylammonium phosphate and 0.045M in (NH4)2HPO4, at pH 7.4). The ion-pair technique offers a high degree of control over the retention characteristics of the herbicide and internal standard. The use of the internal standard permits precise and accurate quantitation and substantially reduces analysis time compared with the external standard method.

Animal Feed↗