An unbiased comparison of organ weights when an inequality in body weight exists

Determining organ weight toxicity with Bayesian causal models: Improving on the analysis of relative organ weights

Regulatory authorities require animal toxicity tests for new chemical entities. Organ weight changes are accepted as a sensitive indicator of chemically induced organ damage, but can be difficult to interpret because changes in organ weight might reflect chemically-induced changes in overall body weight. A common solution is to calculate the relative organ weight (organ to body weight ratio), but this inadequately controls for the dependence on body weight - a point made by statisticians for decades, but which has not been widely adopted. The recommended solution is an analysis of covariance (ANCOVA), but it is rarely used, possibly because both the method of statistical correction and the interpretation of the output may be unclear to those with minimal statistical training. Using relative organ weights can easily lead to incorrect conclusions, resulting in poor decisions, wasted resources, and an ethically questionable use of animals. We propose to cast the problem into a causal modelling framework as it directly assesses questions of scientific interest, the results are easy to interpret, and the analysis is simple to perform with freely available software. Furthermore, by taking a Bayesian approach we can model unequal variances, control for multiple testing, and directly provide evidence of safety.

The relationship between chemical-induced kidney weight increases and kidney histopathology in rats

The kidney is a major site of chemical excretion, which results in its propensity to exhibit chemically-induced toxicological effects at a higher rate than most other organs. Although the kidneys are often weighed in animal toxicity studies, the manner in which these kidney weight measurements are interpreted and the value of this information in predicting renal damage remains controversial. In this study we sought to determine whether a relationship exists between chemically-induced kidney weight changes and renal histopathological alterations. We also examined the relative utility of absolute and relative (kidney-to-body weight ratio) kidney weight in the prediction of renal toxicity. For this, data extracted from oral chemical exposure studies in rats performed by the National Toxicology Program were qualitatively and quantitatively evaluated. Our analysis showed a statistically significant correlation between absolute, but not relative, kidney weight and renal histopathology in chemically-treated rats. This positive correlation between absolute kidney weight and histopathology was observed even with compounds that statistically decreased terminal body weight. Also, changes in absolute kidney weight, which occurred at subchronic exposures, were able to predict the presence or absence of kidney histopathology at both subchronic and chronic exposures. Furthermore, most increases in absolute kidney weight reaching statistical significance (irrespective of the magnitude of change) were found to be relevant for the prediction of histopathological changes. Hence, our findings demonstrate that the evaluation of absolute kidney weight is a useful method for identifying potential renal toxicants.

Relationships between organ weight and body/brain weight in the rat: what is the best analytical endpoint?

Analysis of organ weight in toxicology studies is an important endpoint for identification of potentially harmful effects of chemicals. Differences in organ weight between treatment groups are often accompanied by differences in body weight between these groups, making interpretation of organ weight differences more difficult. Using data from control rats that were part of 26 toxicity studies conducted under similar conditions, we have evaluated the relationship between organ weight and body/brain weight to determine which endpoint (organ weight, organ-to-body weight ratio, or organ-to-brain weight ratio) is likely to accurately detect target organ toxicity. This evaluation has shown that analysis of organ-to-body weight ratios is predictive for evaluating liver and thyroid gland weights, and organ-to-brain weight ratios is predictive for evaluating ovary and adrenal gland weights. Brain, heart, kidney, pituitary gland, and testes weights are not modeled well by any of the choices, and alternative analysis methods such as analysis of covariance should be utilized.

Inhalation toxicity of high flash aromatic naphtha

A petroleum distillate--a high aromatic naphtha--consisting of a 50/50 blended mixture of equivalent products. SHELLSOL A* and SOLVESSO 100**, containing C9 isomers (75 percent) particularly trimethyl benzenes, was examined for systemic toxicity in rats by inhalation exposure. A preliminary 13-week inhalation study with SHELLSOL A had resulted in liver and kidney weight increases in female rats at the high (7400 mg/m3) and medium (3700 mg/m3) exposure levels, and a low grade anaemia in females at all exposure levels (7400, 3700 and 1800 mg/m3). The follow-up 12-month inhalation study in rats described here used atmosphere generated from the SHELLSOL A/SOLVESSO 100 blend of 1800, 900 and 450 mg/m3. Initial reduction in body weight gain occurred in both male and female rats at the higher exposures. Various statistically significant haematological changes were transiently seen in males up to six months, but were not considered biologically significant. High exposure male liver and kidney weights were increased at 6 and 12 months but, in the absence of histopathological changes, were considered to be physiological adaptive responses. No treatment-related histopathological abnormalities were found. It is concluded that chronic exposure to this high aromatic naphtha is without systemic toxicity in rats under the conditions of these studies.

Biochemical, hematological, and histological changes in B6C3F1 mice after intramuscular administration of PROven

Repeated intramuscular administration of PROven to B6C3F1 mice has a potential cardiotoxic effect, an immunogenic effect, and a hematological effect. A significant decrease in two lactic dehydrogenase isoenzymes of myocardial origin was a result of chronic administration of PROven. The immunological effect was observed as a significant increase in beta- and gamma-globulins. The hematological effect of PROven was to increase the number of circulating neutrophils. Both the immunogenic and hematological effect should be anticipated due to the foreign protein nature of PROven. Following intramuscular injections of PROven, severe inflammatory changes including necrosis of skeletal muscle tissue were seen histologically.

Short-term toxicity study in rats of chlorinated cake flour

Male and female Wistar rats were fed for 28 days on a diet containing either chlorinated (1257 or 2506 ppm chlorine) or unchlorinated flour. No significant differences between groups in body weight were observed in the males. A significant inverse correlation between body weight and treatment level, attributable to a corresponding trend in food intakes, was found for the females only. No significant differences between absolute organ weights were found, but when the weights were adjusted for covariance with body weight, dose-related increases in kidney weight (males) and liver weight (both sexes) were found. Histopathological examination revealed no pathological tissue changes attributable to the chlorination of the flour.

The effect of prolonged propranolol administration on myocardial transmural capillary density in young rabbits

1. As a sequel to previous evidence that prolonged beta-adrenoceptor blockade in young rabbits led to a relative increase in the capillarity of ventricular muscle, an attempt has been made to localize and quantify the capillary density from epicardium to endocardium in 12-week old rabbits treated for 6 weeks with propranolol (3 mg kg-1) S.C. twice daily and in litter-mates treated with saline (controls). 2. Full-thickness 0.5 micrometers sections of the left ventricular wall were point-counted in 200 micrometers steps. In the controls the capillary 'volume density' decreased progressively below the epicardial surface from a value of 9% to reach a minimum of 7.1% at a depth of 2.5 mm. Capillary density then increased again towards the endocardium, reaching a maximum of 11.5% in the trabeculae carnae (depth 3.5 mm). 3. In the treated animals the capillary density was increased in the mid wall at 2.3 and 2.5 mm, but significantly decreased in the trabeculae at 3.7 mm (P less than 0.05). 4. A more detailed analysis was undertaken at depths of 0.7 (Epi), 2.3 (Endo) and 3.5 mm (Trab), comprising estimates of capillary number, capillary diameter and intercapillary distance, via the stereological parameters of mean intercept length and mean free distance. 5. In the controls the order was Epi greater than Trab greater than Endo for number, Trab greater than Endo greater than Epi for diameter and Endo greater than Epi greater than Trab for intercapillary distance. 6. In the treated rabbits the mean intercapillary distance was significantly reduced in the epicardial (by 17.5%, P less than 0.05) and endocardial zones (by 32%, P less than 0.005), but was not significantly altered (+3.7%, P greater than 0.05) in the trabeculae. 7. The non-uniform distribution of capillaries in the controls illustrates that detection of changes in transmural capillary density requires that the depth of samples be measured from the epicardial surface and not, owing to the presence of trabeculae carnae, from the endocardium. 8. If similar treatment effects were to occur in man, they would suggest that prolonged beta-blockade could induce an increase in capillary density which would render the ventricular mid wall less susceptible to ischaemia.