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61.
Enlarged hock joints were observed during 1983 in B6C3F1 mice of chronic toxicity and carcinogenicity studies sponsored by the National Toxicology Program (NTP). Subsequently, approximately 9,500 B6C3F1 mice on 32 NTP chemical toxicity and carcinogenicity studies were evaluated for this condition by clinical examination. Group caged male B6C3F1 mice had thickening and reduced mobility of the hock joints at prevalences of 1.2% up to 6 months of age; 23% at 6 to 12 months of age; and 62% at 13 to 26 months of age. Group caged female B6C3F1 mice had a prevalence of 2% or less. Histologically, affected mice had periarticular exostoses on the bones of the hock joints, with formation of bony bridges around joints and deposition of new bone in joint spaces, resulting in partial or complete ankylosis. Individually caged male and female B6C3F1 mice were not affected. The cause of the ankylosis was not determined, but its occurrence in the NTP studies has been reduced by individual caging. 相似文献
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63.
Acute tolerance to the cardiovascular effects of cocaine has been hypothesized from experiments in which the plasma concentrations of cocaine were rapidly changing. We studied the cardiovascular responses of 8 male human subjects for 4 hours following intravenous bolus doses of cocaine, and compared these to responses in the same subjects after intravenous bolus doses of cocaine followed by continuous intravenous infusions of cocaine designed to maintain steady state plasma levels of cocaine. We found little evidence of tolerance to the tachycardia and hypertensive effects of cocaine during a four hour exposure. Lack of tolerance to the cardiovascular effects of cocaine may be a factor in some types of cocaine related toxicity among cocaine abusers. 相似文献
64.
M van Duin J H Janssen J de Wit J H Hoeijmakers L H Thompson D Bootsma A Westerveld 《Mutation research》1988,193(2):123-130
The human DNA-excision repair gene ERCC-1 is cloned by its ability to correct the excision-repair defect of the ultraviolet light- and mitomycin-C-sensitive CHO mutant cell line 43-3B. This mutant is assigned to complementation group 2 of the excision-repair-deficient CHO mutants. In order to establish whether the correction by ERCC-1 is confined to CHO mutants of one complementation group, the cloned repair gene, present on cosmid 43-34, was transfected to representative cell lines of the 6 complementation groups that have been identified to date. Following transfection, mycophenolic acid was used to select for transferants expressing the dominant marker gene Ecogpt, also present on cosmid 43-34. Cotransfer of the ERCC-1 gene was shown by Southern blot analysis of DNA from pooled (500-2000 independent colonies) transformants of each mutant. UV survival and UV-induced UDS showed that only mutants belonging to complementation group 2 and no mutants of other groups were corrected by the ERCC-1 gene. This demonstrates that ERCC-1 does not provide an aspecific bypass of excision-repair defects in CHO mutants and supports the assumption that the complementation analysis is based on mutations in different repair genes. 相似文献
65.
Summary Plants of white clover Trifolium repens were grown under the canopies of three grass species, Lolium perenne, Agrostis tenuis and Holcus lanatus, and under simulated canopies of black polythene and controls were exposed to unfiltered natural radiation. The canopies were adjusted so that they transmitted equal intensities of Photosynthetically Active Radiation (P.A.R.). The ratio of red to far red radiation () was unchanged under the black polythene canopies but was reduced under canopies of Lolium and Agrostis and even more so under Holcus. The effect of canopy filtered radiation on the growth of clover was greatly to reduced internode length, mean number of nodes, the number of branched nodes and the number of rooted nodes and greatly to increase petiole length. The effect of canopies of Holcus was greater than that of the other grass species both in its effect on and on the responses of the clover plant to its shade. 相似文献
66.
G H Greeley Y S Guo G Gomez F Lluis P Singh J C Thompson 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1988,189(3):325-328
The purpose of this study was to determine whether the inhibitory action of peptide YY (PYY) on gastric acid secretion is attributable to the release of gastric somatostatin in rats. Two groups of rats (six rats/group) were anesthetized with urethane and prepared with gastric fistulas and jugular catheters. Pentagastrin (18 micrograms/kg-h) was given intravenously for 150 min to stimulate gastric acid secretion. Intravenous PYY (130 micrograms/kg-h) inhibited pentagastrin-stimulated gastric acid secretion significantly (P less than 0.05). Administration of iv PYY resulted in a 41% reduction (P less than 0.05) in pentagastrin-stimulated gastric acid secretion. In another group of anesthetized rats, administration of PYY (10(-7), 10(-8) M) failed to stimulate a release of somatostatin from the isolated-perfused rat stomach. Our findings indicate that PYY can inhibit gastric acid secretion independently of release of gastric somatostatin in the rat. 相似文献
67.
The joint probability distribution of the number of distinct (not identical by descent) genes from each founder of the Equus przewalskii population that survive in the five horses of the Calgary Zoological Gardens breeding group has been calculated. The dependence structure of this distribution is investigated, and informative marginal distributions are given, among them the distributions of the genetic contributions of each founder to the Calgary horses and the distribution of wild-type genes in these horses. The dependence pattern is found to be complex; there is no substitute for exact calculation of the full joint probability distribution of numbers of surviving genes. Probabilities of gene survival give a more complete summary of the genetic structure of a set of individuals than is provided by more routine measures such as heterozygosity or founder contributions. The feasibility of computing these probabilities for small groups of current individuals descended from few founders via long and complex pedigrees, provides a new approach to assessing such groups, and could be used also in selecting animals to form the founder stock of propagules for future reintroduction programs. 相似文献
68.
R Peto R Gray R Collins K Wheatley C Hennekens K Jamrozik C Warlow B Hafner E Thompson S Norton J Gilliland R Doll 《BMJ (Clinical research ed.)》1988,296(6618):313-316
A six year randomised trial was conducted among 5139 apparently healthy male doctors to see whether 500 mg aspirin daily would reduce the incidence of and mortality from stroke, myocardial infarction, or other vascular conditions. Though total mortality was 10% lower in the treated than control group, this difference was not statistically significant and chiefly involved diseases other than stroke or myocardial infarction. Likewise, there was no significant difference in the incidence of non-fatal myocardial infarction or stroke—indeed, disabling strokes were somewhat commoner among those allocated aspirin. The lower confidence limit for the effect of aspirin on non-fatal stroke or myocardial infarction, however, was a substantial 25% reduction. Migraine and certain types of musculoskeletal pain were reported significantly less often in the treated than control group, but as the control group was not given a placebo the relevance of these findings was difficult to assess. There was no apparent reduction in the incidence of cataract in the treated group.The lack of any apparent reduction in disabling stroke or vascular death contrasts with the established value of antiplatelet treatment after occlusive vascular disease. 相似文献
69.
70.