Production of low-fatmilk. I. Effect of quality and quantity of concentrate on the volatile fatty acids of the rumen and on the composition of the milk.
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Animals↗
Biomedical subjects
T R Lewis
Publications and source records attributed to T R Lewis.
Subchronic inhalation of triethylamine vapor in Fischer-344 rats: organ system toxicity.
Male and female F-344 rats were exposed at 0, 25, or 247 ppm triethylamine (TEA) vapor, 6 hr per day, 5 days per week for up to 28 weeks in order to characterize the subchronic organ system toxicity. Rats were weighed biweekly and scheduled sacrifices were performed following about 30, 60, and 120 days of exposure. No statistically significant treatment-related effects on organ weights, hematology, clinical chemistry, or electrocardiographic indices were observed. Body weight gain was not affected by TEA treatment. No physiologic or pathologic evidence of cardiotoxicity was seen in rats exposed to either TEA concentration for up to 28 weeks. No gross or histopathologic lesions attributable to TEA exposure were noted in any of the organs examined, including the nasal passages. This latter finding is in marked contrast to previously reported findings from this laboratory in which squamous metaplasia, suppurative rhinitis, and lymphoid hyperplasia were found in the respiratory epithelium of F-344 rats exposed to the structurally related chemical, diethylamine, under the same conditions as this study (Lynch et al., 1986).
Administration, Inhalation↗
Neurobehavioral effects of methyl N-butyl ketone and methyl N-amyl ketone in rats and monkeys: a summary of NIOSH investigations.
The results from four NIOSH investigations concerning the neurobehavioral effects of methyl n-butyl ketone (MBK) and methyl n-amyl ketone (MAK) on experimental animals are summarized. The investigations were initiated following clinical reports of neurologic sequelae in humans exposed to these ketone solvents. In order to explore both acute and chronic effects of MBK and MAK, two general types of studies were conducted: 1) neurophysiologic evaluation of monkeys and rats following chronic inhalation, and 2) behavioral effects in rats following oral or intraperitoneal administration. Results from chronic inhalation studies after 4 months of 1000 ppm MBK exposure (all exposures: 6 hrs/day, 5 days/week) showed the following: decreased motor nerve conduction velocities (NCV) in the ulnar and sciatic-tibial nerves, reduced amplitude of evoked muscle action potentials (MAP), lengthened latency of components of the visual evoked brain potential, decreased body weight, and hindlimb drag. Decrements in sciatic-tibial NCV and MAP amplitude were found after 9 months exposure to 100 ppm MBK. In contrast, exposure to approximately 1000 ppm MAK for 9 months had no adverse affects on neurophysiologic indicators of nervous system integrity. Dose-response investigations of the effects of MBK (oral) and MAK (ip) showed for both solvents a reduction in the response rate of rats trained on a multiple schedule of reinforcement.
Action Potentials↗
Toxicity of low concentration long-term exposure to an airborne mixture of nitrous oxide and halothane.
To evaluate experimentally the questions of reproductive, teratological, cytogenetic, and tumorigenic sequelae of long-term exposures to escape levels of halothane plus nitrous oxide (N2O), male and female rats were exposed either to air, to 1 ppm halothane plus 50 ppm N2O, or to 10 ppm halothane plus 500 ppm N2O for 7 hr/day, 5 days/wk for appropriate periods of time. In one experiment, young adult female rats were exposed for 60 days, then mated and reexposed either staring with Day 1 or Day 6 of gestation until Day 15. The former were permitted to deliver naturally while the latter were delivered by C-section on Day 20. The young adult males used in breeding were also exposed for 60 days prior to mating and then for a total of 52 weeks thereafter. At termination, bone marrow cell and spermatogonial metaphase preparations were made and assessed for cytogenetic abnormalities. The mated females were evaluated for ovulation, pre- and post-implantation loss, fetal growth, fetal abnormalities, and early post-natal development, as appropriate. In a parallel experiment, 50 male and 50 female weanling rats in each group were exposed for 104 weeks to the same levels and then evaluated for tumor development with emphasis on the reticuloendothelial system. The results indicated a significant reduction in ovulation and implantation efficiency from exposure to the higher levels and slightly retarded fetal development at both levels. No teratological or abortifacient effects were noted. No tumorogenic effects were observed. However, cytogenetic damage to both bone marrow and spermatogonial cells was seen at both levels.
Air Pollutants↗
Subchronic inhalation toxicity of nitromethane and 2-nitropropane.
Nitromethane (NM) and 2-nitropropane (2-NP) and versatile compounds employed in a wide variety of industrial applications, thus providing ample opportunity for occupational exposure. The purpose of this study was to determine the subchronic inhalation toxicity of NM and 2-NP in order to recommend acceptable exposure levels in the workplace. Fifty male rats and 15 male rabbits were exposed to either 98 ppm or 745 ppm of NM or 27 or 207 ppm of 2-NP 7 hours/day, 5 days/week, for periods up to 24 weeks. Fifty rats and 15 rabbits were exposed to filtered air for similar lengths of time and served as controls. Ten rats from each exposure and control group were sacrificed following 2 days, 10 days, 1 month, 3 months, and 6 months of exposure. Five rabbits from each exposure or control group were sacrificed at 1, 3, and 6 months of exposure. Effects relatable to exposure to NM were decreased body weight gain in rats following 8 weeks of exposure to 745 ppm, and a thyroid effect evidenced by an increased thyroid weight and decreased serum thyroxin levels, most notable in rabbits. Liver weights were significantly elevated in rats exposed to 207 ppm of 2-NP for 1, 3, and 6 months. No exposure-related gross or microscopic alterations were seen in any of the tissues examined for rats and rabbits exposed to 745 and 98 ppm of NM and 27 ppm of 2-NP or in tissues of rabbits exposed to 207 ppm of 2-NP. Liver neoplasms were seen in all 10 rats killed following 6 months of exposure to 207 ppm of 2-NP, indicating that 2-NP is a potent carcinogen in the rat.
Animals↗