Authors of papers in biological journals need to make their uses of statistical methods and software explicit and maximally comprehensible. Editors and referees have important responsibilities for this. Inexact use of technical terminology causes confusion. Computer software is invaluable but not infallible. Graphical presentation should not conceal numerical results. Tests of statistical significance should be reserved for specific needs, which will rarely include multiple comparison procedures. Experiments that involve repeated measurements need special care in statistical analysis. Full attention should be given to principles of statistical estimation as well as to choice of appropriate statistical technique. At all times, ethical standards of scientific integrity must contribute to precision and clarity. Clinical research that neglects well-established statistical principles may be intrinsically unethical.
Both male and female guinea pigs are widely used in tests to detect the skin-sensi-tizing potential of new chemicals. The aim of the present study was to investigate the influence of the animal gender on sensitization rates, with the guinea-pig maximization test (GPMT) using OECD recommended positive control sensitizers, and the differences of the density of Langerhans cells in male and female guinea pigs. The sensitization rates of males and females challenged with HCA, MBT or benzocaine gave almost the same results. There were no statistical differences between the mean responses of males and females. These results were confirmed by rechallenge with the OECD recommended positive controls. Furthermore, the density of Langerhans cells in abdominal epidermis in males (1229±45cells/mm2) was the same as that in females (1242±89cells/mm2). These results indicate that there is no significant influence of guinea-pig gender in the assessment of skin-sensitizing potential using the GPMT.
In this study, we examined whether the production of hydrogen peroxide by peroxisome proliferators causes oxidative DNA damage in the form of 8-oxodeoxyguanosine (8-oxodG) and hepatic injury, and whether it is related to their tumor-promoting or carcinogenic activities in female rats treated with the peroxisome proliferators clofibrate and perfluorodecanoic acid (PFDA). Clofibrate has tumor-promoting and carcinogenic activities, whereas PFDA does not. We also tested whether peroxisome proliferators directly induce mutagenic events in Salmonella typhimurium strains TA 98 and TA 1537. Rats were treated either by 5% clofibrate in diet or by an i.p. injection of corn oil containing 10 mg/kg body weight of PFDA every week for 2 or 8 weeks. 8-OxodG in liver DNA was analyzed by HPLC coupled with an electrochemical detector. Hepatic injury was evidenced by liver enlargement and by levels of serum enzymes, aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and hepatic γ-glutamylpeptidase (γ-GT) activity. Clofibrate and PFDA increased the activity of catalase about or less than 2-fold, whereas FAO activity was increased about 6 to 7-fold by clofibrate and about 3 to 4-fold by PFDA. Neither clofibrate nor PFDA induced mutation at any dose tested. Clofibrate significantly increased the formation of 8-oxodG, but PFDA only slightly increased. Serum AST and ALT levels, and hepatic γ-GT activity were not significantly changed at both time points, whereas the ratio of liver/body weight was significantly increased by clofibrate and PFDA at 8 weeks. These data imply that the magnitude of the production of hydrogen peroxide-generated FAO is related to the induction of oxidative DNA damage by peroxisome proliferators, and their tumor-promoting or carcinogenic activities. However, the effect of hydrogen peroxide in hepatic injury is not clear.
Experimental cutaneous calcification was induced by a subcutaneous injection of lead acetate in parathyroidectomized (PTX) rats and vitamin D-deficient rats whose plasma calcium concentrations were controlled by diets containing various amounts of calcium. Although, in PTX rats, the calcium content of the calcified plaque induced by lead acetate was correlated with their plasma calcium concentration, calcium content of the calcified plaque in vitamin D-deficient rats with normocalcemia was significantly lower than those in control and PTX rats with normocalcemia. A subcutaneous administration of 1α, 25-dihydroxyvitamin D3 (1α, 25(OH)2D3) following the lead acetate injection increased calcium content of the calcified plaque in vitamin D-deficient mice, suggesting the involvement of vitamin D in the cutaneous calcification. As the synthesis of osteocalcin, osteopontin and interleukin-1 (IL-1) receptor is well known to be increased by 1α, 25(OH)2D3, gene expressions of mRNAs of these proteins were examined in the skin with calcified plaque by reverse transcription polymerase chain reaction (RT-PCR) analysis. These mRNA expressions in the skin with calcified plaque were increased by a subcutaneous administration of 1α, 25(OH)2D3 following the lead acetate injection. On the contrary, they decreased in vitamin D-deficient mice. These findings suggest that vitamin D is directly involved in the process of experimental calcification.
The protective effects of 1, 3-dithia-2-thioxo-cyclopent-4-ene (DT827A), 4-phenyl-1, 3-dithia-2-thioxo-cyclopent-4-ene (DT827B) and 4-(4-fluorophenyl)-1, 3-dithia-2-thioxo-cyclopent-4-ene (DT827C) on liver injury induced by D-galactosamine plus carbon tetrachloride (D-GalN+CCl4)and that of DT827B on liver injury induced by thioacetamide were studied using male rats. Out of the three DT827 series of compounds, DT827B was more effective on liver injury induced by the combination exposure to D-GaIN+CCl4 for 4 weeks, and accordingly the following two experiments were carried out using DT827B only. Twelve-week administration of DT827B at dose levels of 5, 10 and 20 mg/kg/day revealed a therapeutic effect against liver injury induced by D-GaIN+CCl4 dose-dependently, and another twelve-week administration of DT827B at the same three dose levels also revealed a therapeutic effect against liver injury induced by thioacetamide dose-dependently. A hepatoprotective potential of DT827B was suggested under the conditions of these studies.
Prothrombin time (PT) and activated partial thromboplastin time (APTT) were studied under excessive sodium citrate using the plasma from rats and beagle dogs. Addition of sodium citrate into the plasma caused a prolongation of PT and APTT. The prolongation was dependent on the concentration of sodium citrate or calculated hematocrit. The degree of prolongation was more severe in rats than in dogs, and in APTT than in PT. These results suggest that an artificial prolongation of PT and APTT occurs under excessive sodium citrate (e.g., elevated hematocrit), and that the degree differs between species and between parameters.