Absorption and disposition of cobalt naphthenate in rats after a single oral dose

The absorption and disposition of inorganic cobalt salts after oral administration have not been completely characterized. The objective of this project was to investigate the absorption and disposition of cobalt naphthenate in Fischer 344 rats following a single oral dose. Cobalt naphthenate was given orally at 3 doses: 0.333, 3.33, or 33.3 mg Co(II)/kg. Tissues, urine, and feces were collected over a 36-h period from the low- and high-dose groups; blood was collected from all 3 dose groups. The majority of the dose in both the low- and high-dose groups was excreted in the feces (42% and 73.1%, respectively), indicating that cobalt was incompletely absorbed from the gastrointestinal tract following oral dosing. The percent of the dose excreted in the urine was similar for low and high doses (31.8% and 26.3%, respectively). Cobalt concentrations were found to be highest in the liver and kidneys. The blood versus time cobalt concentration curves for the low-dose, intermediate-dose, and high-dose groups were elevated 4- to 5-fold, 14- to 25-fold, and 25- to 60-fold over control blood levels, respectively. The peak plasma concentrations of 0.6 and 1.7 microg Co(II)/ml occurred at approximately 4.3 h for the intermediate-dose group, and 3.3 h for the high-dose group. The terminal elimination half-lives were 24.7 and 24 h for the intermediate- and high-dose groups, respectively. Thus, although the extent of cobalt absorption as indicated by the blood concentrations and areas under the blood-time curves was not proportional to dose, the calculated pharmacokinetic values for the time to peak blood concentration and the apparent elimination rate constants were independent of dose. The amount excreted in the urine was also proportional to the dose. These apparent anomalies were not related to protein binding in blood.

Disposition, toxicity, and intestinal absorption of cobaltous chloride in male Fischer 344 rats

The absorption and disposition of inorganic cobalt salts after oral administration have not been well characterized. The objectives of this study were to compare in vivo results with cobalt transport through the in vitro everted small intestine and to relate the disposition results to a biochemical indicator of cobalt toxicity. Cobalt chloride was given to male Fischer 344 rats orally at 33.3 mg Co(II)/kg or intravenously at 4.16 mg Co(II)/kg. By 36 h, 74.5% of the oral dose was eliminated in the feces. The liver, kidney, and heart accumulated cobalt to the greatest extent. Following the single oral dose, the blood cobalt concentration-time curve was triphasic, peaked at 3.2 h, and had an absorptive half-life of 0.9 h, an elimination phase half-life of 3.9 h, and a terminal elimination half-life of 22.9 h. Following intravenous administration, 10.1% of the dose was excreted in the feces, indicating that cobalt can be secreted in the bile. Following a single intravenous injection, the concentration-time curve displayed three segments. The first segment, which occurred during the first 4 h, had a rapid half-life of 1.3 h. The second phase, from 4 to 12 h, demonstrated a slower clearance rate with a half-life of 4.3 h. The final and slowest phase, from 12 to 36 h, had a half-life of 19 h. Intestinal jejunal ring experiments indicated that cobalt transport has both active and passive components; however, cobalt transport through the in vitro rat everted duodenum indicated that cobalt transport had almost exclusively passive components with facilitated diffusion. The finding that uptake was saturable may explain the small extent of absorption following oral dosing. Heme oxygenase studies following subcutaneous and intravenous administration resulted in an increase in activity (twofold) over controls, while oral administration did not. We concluded that the extent of cobalt absorption across the gastrointestinal tract is incomplete, and that the concentration administered and the route of exposure may determine its systemic toxicity.

Comparative 90-day feeding study with low-viscosity white mineral oil in Fischer-344 and Sprague-Dawley-derived CRL:CD rats

A 90-day study was conducted to compare the effects of dietary administration of a food-grade white oil in female Fischer-344 (F-344) and Sprague-Dawley-derived (CRL:CD) rats. Animals were fed a low viscosity (15 mm2/sec at 40 degrees C) paraffinic white oil (designated as P 15[H]) at 0, 0.2, or 2.0% of the diet for 30, 61, or 92 days. There were no significant adverse clinical observations or unscheduled deaths. In the F-344 rats, occasional treatment-related changes were seen in hematology and clinical chemistry parameters. At necropsy, mesenteric lymph nodes were enlarged, and there was an increase in absolute and relative liver, mesenteric lymph node, and spleen weights as compared to controls. Histopathologic effects included hepatic and mesenteric lymph node microgranulomas and mesenteric lymph node histiocytosis. In CRL:CD rats, the only effects noted were accumulations of chronic inflammatory cells in the liver at the high dose only, without the formation of discrete microgranulomas. A dose-related increase in mineral hydrocarbon (MCH) material in the liver and mesenteric lymph nodes was observed in both F-344 and CRL:CD rats. Although increased, liver MhC content was significantly less (approximately 50%) in CRL:CD rats than the levels detected in the F-344 rats. Mesenteric lymph node MHC levels did not differ significantly between the strains. This study demonstrated strain differences among rats in histopathologic effects of white oil, with the CRL:CD rat essentially showing no response compared to the F-344 rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of fluidizing bed aerosol generators to establish a dust mixture of two substances at a fixed ratio for inhalation toxicity studies

A method was developed to use two fluidizing bed generators to deliver a mixture of 1 mg cobalt + 15 mg tungsten carbide/m3 to an inhalation exposure chamber with the output from the cobalt generator split to provide the same cobalt concentration to a cobalt-only chamber. To provide a more uniform delivery of material and to minimize the amount of starting dust needed, a subsystem that produced timed bursts of compressed air was used to prevent the accumulation of dust along the aerosol transport tubes. The addition of an electrostatic precipitator placed in the exhaust lines reduced the amount of dust delivered to the high-efficiency particulate air filters, thereby reducing the number of filter changes.