Melvin W. Carter

Covariance analyses with heterogeneity of slopes in fixed models.

Techniques that describe the use of covariance when heterogeneity of slopes exists are severely limited. Although a few procedures for model selection have been recommended, none, except the hierarchical approach, is straightforward and usable with present computer programs. The hierarchical subset selection procedure presented in this paper is based on the proposition that heterogeneity may be present only for certain terms in the model. After hierarchical selection, those terms which do not involve heterogeneity are interpreted as in the usual analysis for covariance. The interpretations of those terms which do involve heterogeneity are modified with respect to significance tests performed at various values of the covariate. The hierarchical subset selection method allows one to investigate heterogeneity of slopes in covariance models as functions of the classification variables present in the design.

Leaf litter processing in aquatic systems: A two variable model

A negative exponential model with one independent variable, days or accumulated time, was examined for adequacy as a descriptive equation for aquatic leaf litter processing. The effect of adding a second independent variable, degree days or accumulated temperature, to the model was also examined. The two variable negative exponential model was shown to have two advantages over the single variable model. The expanded model provided an adequate fit of litter processing data for more cases than the single variable model. Also, the two variable model allowed determination of rate coefficients corresponding to each temperature level of the experiment rather than assuming a single, constant rate coefficient as with the one variable model. The trends of the temperature dependent rate coefficients were useful for examining processing differences between experiments for different sites and seasons.

Developmental toxicity of nine selected compounds following prenatal exposure in the mouse: naphthalene-, p-nitrophenol, sodium selenite, dimethyl phthalate, ethylenethiourea, and four glycol ether derivatives

Ethylene glycol dimethyl ether (EGdiME), diethylene glycol dimethyl ether (diEGdiME), triethylene glycol dimethyl ether (triEGdiME), diethylene glycol diethyl ether (diEGdiEE), ethylenethiourea (ETU), sodium selenite (SS), dimethyl phthalate (DMP), naphthalene (NAP), or p-nitrophenol (PNP) were administered by gavage for eight consecutive days to female CD-1 mice. Weight loss was insensitive as an index of sublethal adult toxicity and was inadequate for determining a maximum tolerated dose. LD50 values indicate that SS, NAP, and PNP were more toxic (8.4, 353.6, and 625.7 mg/kg, respectively) than the polyglycol ethers, ETU, and DMP (LD50 values ranged from 2525.8 to 6281.9 mg/kg). Each of the compounds was administered on d 7 through 14 to pregnant animals at a single dose estimated to be at or just below the threshold of adult lethality. In such a reproductive study, each of the compounds could be categorized on the basis of the pattern of maternal lethality and fetotoxicity which it produced. The number of dams with complete resorptions was significantly increased after administration of ETU, and no mice in the EGdiME-, diEGdiME-, or triEGdiME-treated groups delivered any viable offspring. Maternal lethality was significant in the EGdiME, triEGdiME, PNP, and NAP groups. There was a slight reduction in the average number of live pups per litter in the diEGdiEE- and PNP-treated groups and a significant reduction in the NAP group. The number dead per litter was increased with diEGdiEE. SS and DMP had no effect on maternal or fetal survival at the doses administered. Individual pup weight at d 1 postpartum was only significantly reduced by diEGdiEE, and no gross congenital abnormalities were detected in neonates from any treatment group. These results provide guidelines for the subsequent toxicity testing of these chemicals.

A developmental toxicity study of tretinoin administered topically and orally to pregnant Wistar rats

BACKGROUND Although it is well established that oral tretinoin produces embryofetal developmental toxicity in various laboratory animals, the toxic potential of topical tretinoin has not been clearly established. OBJECTIVE This study of tretinoin administration to pregnant Wistar rats was conducted to determine whether topical tretinoin is associated with adverse effects on reproductive function or embryofetal growth and development and to compare outcomes with topical and oral tretinoin. METHODS Topical and oral tretinoin (1 to 20 mg/kg and 1 to 10 mg/kg, respectively) or vehicles alone were administered on gestational days 6 through 16 and 15, respectively. RESULTS Topical tretinoin: After topical treatment, dams receiving 10 mg/kg daily or greater had severe local and systemic toxicity prompting discontinuation of tretinoin. At doses of 2.5 mg/kg or greater, dam weight gain and food consumption were significantly less than those of control dams. Offspring of dams receiving 5 mg/kg weighed significantly less, and offspring of dams receiving 2.5 mg/kg or greater had a significantly greater occurrence of supernumerary ribs compared with control offspring. Oral tretinoin: After oral treatment, in the absence of maternal toxicity, significantly more offspring of dams receiving 5 mg/kg or greater had supernumerary ribs, and offspring of the 10 mg/kg treatment group had a greater incidence of cleft palate than had control offspring. CONCLUSION The local and systemic maternal toxicity found in association with supernumerary ribs and low weights in the offspring at topical tretinoin doses of 2.5 and 5 mg/kg suggests that these developmental effects may be nonspecific or maternally mediated. Oral tretinoin at doses of 10 mg/kg, however, is clearly associated with embryofetal alterations in the Wistar rat.

Induction of maternal toxicity in the rat by dermal application of retinoic acid and its effect of fetal outcome

Time-mated Sprague-Dawley rats were administered all-trans-retinoic acid (RA) dermally on gestational days 11 through 14 at three dosage levels (25, 100, and 250 mg/kg body weight). Dams administered ethylenethiourea (ETU) dermally on gestational days 11 to 12 or RA orally on day 12 were used to indicate the strains sensitivity to teratogenesis. The chemicals were dissolved in dimethylsulfoxide (DMSO) for dermal application or suspended in corn oil for treatment by gavage. The maternal weight gain, pup weight, number of resorptions and number of fetuses with gross malformations, and skeletal/organ-level anomalies were determined. Beginning with day 15, dams dermally treated with RA exhibited dermal lesions at the site of application, most dams showed vaginal bleeding by day 16, and approximately 20% did not survive to day 19. Relative to the DMSO control group, maternal weight gain in the dermal RA groups was decreased by approximately 50% at the lowest dose, with essentially no weight gain at the intermediate- and high-dose levels. The decrease in average fetal weight at the two higher doses was significant, whereas the resorption and malformation frequencies were not significantly increased by dermal treatment with RA. Without significantly affecting fetal weight or resorption frequency, dermal application of ETU significantly increased the frequency of skeletal anomalies, primarily tail defects. Oral administration of RA did not increase the malformation frequency nor produce significant maternal or fetotoxic effects. In summary, treatment of pregnant Sprague-Dawley rats by dermal application of RA dissolved in DMSO resulted in significant toxicity to the dam.(ABSTRACT TRUNCATED AT 250 WORDS)

A Comparison of Five Statistical Methods for Analyzing Pretest-Posttest Designs.

Five methods for analyzing data arising from research involving pretests and posttests are considered. These methods include: (1) posttest analysis only; (2) analysis of raw gain scores (posttest minus pretest); (3) analysis of the data with a pretest-posttest factor included in the statistical model; (4) analysis of posttest data with pretests as a covariate, and (5) analysis of gain scores with pretests as a covariate. The characteristics of each are discussed, with a conclusion that the fifth method is superior to the others when the assumptions underlying covariance analysis are met.

Effects of dietary endrin on reproduction of mallard ducks (Anas platyrhynchos)

Effects of dietary endrin treatments (0.5 and 3.0 ppm) on development, egg production, and accumulated residue in treatment adults and their eggs were examined for mallard ducks (Anas platyrhynchos). Egg production, fertility, and hatchability were not affected, although a 9.6% drop in embryo survival was observed for the 3.0 ppm treatment. Hatchling survival to 14 days was not affected by endrin treatments. Males treated with 3.0 ppm sustained a 4.5% loss in body weight. Treated females developed a higher body fat content and greater accumulation of endrin than males. Endrin was deposited in the eggs of treated females at about the same dietary concentration of endrin in their feed.

Estimation and hypothesis in linear models-A reparameterization approach to the cell mlans modll

A general approach to analysis of fixed effects models through a reparameterization of the cell means model is outlined. After applying a Q-op3rator, distribution theory for the model is developed. Methods of estimation and hypothesis testing are given and the exact form of each hypothesis is shown. The implementation of these results in a currently available computer package is discussed.

Latin square changeover design in physical education research.

Abstract The Latin square changeover design, which may be applied to the study of physiological parameters, is investigated. The utility of the design in relation to identifying and estimating residual treatment effects is discussed, with an example of an application of the design. The example involves a caloric cost study in which each subject receives six different treatments. Therefore, the possibility of carry-over effects is considered. Analysis techniques are discussed, including problems related to the confounding of effects resulting from the designs nonorthogonality. The magnitudes of the carry-over effects are calculated. Finally, the design is compared to the randomized block and Latin square designs, and the relative efficiency of the changeover design is demonstrated.

Purification and kinetics of Δ1-pyrroline-5-carboxylate reductase from Drosophila melanogaster

Δ1-Pyrroline-5-carboxylate reductase has been purified 650-fold from homogenized whole, adult Drosophila melanogaster. Affinity chromatography on Blue Sepharose CL-6B yielded a 50-fold purification in a single step. The enzyme utilizes either NADPH or NADH as cofactor. It can oxidize proline and reduce NADP+ at pH 9.6. The data are consistent with the possibility that the reaction mechanism is of the Bi Bi Ping Pong type with both substrate and cofactor inhibiting at high concentrations.