Excess mortality in two-year rodent carcinogenicity studies.

This paper considers the impacts of various patterns of differential or excess mortality on the biological and statistical interpretation of 2-year rodent carcinogenicity studies. It provides suggestions on experimental design that are intended to maximize the value of such studies for carcinogenic risk assessment. Specifically, it recommends dose reduction, possibly to the level of dose cessation, when biologically feasible and considers the merits of termination of the entire study as alternatives to the commonly employed strategy of terminating particular dose groups. It then recommends statistical analysis modifications that are appropriate when these suggestions on experimental design are adopted. One of the recommended modifications is a new statistical test to determine whether a dose group exceeds the maximum tolerated dose (MTD) on the basis of mortality. While the authors provide recommendations for the most commonly occurring exigencies, they acknowledge the need for and strongly support the practice of active engagement of the appropriate regulatory agency, e.g., the FDA, prior to any action.

Echocardiography, a non-invasive method for the investigation of heart morphology and function in laboratory dogs: 1. Method and reference values for M-mode parameters.

We have set up M-mode echocardiographic (EC) recording in beagles in our laboratory and generated reference values for EC indicators of left ventricle function and morphology. Additionally we assessed the effects of sex, strain and body weight on these parameters and the correlation between parameters. M-mode EC under two-dimensional guidance in longitudinal section was performed on 59 male and 49 female beagles from Marshall (USA) and 13 males and 13 females from Harlan (France). The following parameters were measured or calculated: left ventricle internal diameter in diastole and systole (LVIDd and LVIDs), left ventricle and diastolic and end systolic and stroke volumes (EDV, ESV and SV), cardiac output and index (CO and CI), fractional shortening (FS), ejection fraction (EF), the thickness of the septum and left ventricle posterior wall in diastole (STd and LVPWd) and systole (STs and LVPWs), the percentage of thickening of the septum and left posterior wall (PST and PWT), and the mean and maximal velocities of the left ventricle posterior wall (PWVm and PWVM). Heart rate (HR) was measured by cardiac auscultation. Marshall dogs have higher left ventricle dimensions but lower amplitude and velocity of contraction than Harlan dogs. There were also statistically significant differences between sexes for a number of EC parameters mainly those relating to the size of the left ventricle walls or cavity in diastole. Overall these differences were explained by the correlation between these parameters and body weight. Heart rate correlated only with PWVm and PWVM. There were positive correlations between PST, PWT and EF or FS and between velocities and FS or EF. EDV correlates negatively with EF, FS, PST or PWT.

Fat, frail and dying young: survival, body weight and pathology of the Charles River Sprague-Dawley-derived rat prior to and since the introduction of the VAFR variant in 1988.

Trends in survival and body weight were evaluated in 2140 control Sprague-Dawley-derived [Crl: COBS-CD(SD)BR and Crl: COBS-VAF CD(SD)BR] rats used for 24-month rat carcinogenicity studies between 1979 and 1991. Body weight and survival were remarkably stable in the CD-COBS rats used during 1979-1987: at 24 months, the mean survival in males was 68 +/- 5%, and 60 +/- 5% in females. With the CD-COBS-VAF rat, a variant of the CD-COBS strain used between 1988 and 1991, the survival at 24 months dropped to 41 +/- 3% in males, and 44 +/- 7% in females compared to the CD-COBS. The CD-COBS-VAF rat had a significantly reduced life span (P < 0.001 at 24 months), a significant increase in mean body weight (males at 6 months: 672 +/- 24 g vs. 536 +/- 6 g; females: 359 +/- 7 g vs 308 +/- 3 g; P < 0.001) and food consumption (males at 6 months: 31.3 +/- 3.3 vs. 25.4 +/- 2.1 g d-1; females: 22.0 +/- 2.7 g v. 20.3 +/- 2.0 g d-1; P < 0.001). CD-COBS-VAF rats which failed to survive up to study termination had individual body weights at 3, 6 and 12 months which were significantly higher (P < 0.001) than those which survived until 24 months. Our historical data base of control rats (CD-COBS and CD-COBS-VAF) in carcinogenicity studies revealed a significant (males: P < 0.001); females: P < 0.01) and inverse linear relation between mean 3-month body weight and 24-month survival. When compared to CD-COBS animals, CD-COBS-VAF rats showed an increase in the incidence of pituitary tumours in males, mammary fibroadenomas in females, an increase in the incidence of severity of glomerulonephrosis, and a greater incidence of animals which died without any obvious pathology. It is concluded that, in our Sprague-Dawley substrains, both the individual and the group mean body weights in early adult life appear predictive for the individual and group life expectancy. The decrease in longevity in the CD-COBS-VAF rat is principally due to disease and degeneration processes associated with fast growth and high body weight.

Nucleolar organizer regions in cardiac lesions induced by doxorubicin.

The use of the argyrophilic (Ag) staining technique for nucleolar organizer regions (NORs) revealed nuclear changes in myocytes of the left atrium of 10 rats treated twice a week for 6 weeks with doxorubicin (1 mg/kg body weight) iv and sacrificed after 6 weeks without treatment. The changes were easily detected qualitatively and further assessed by quantification. Cardiac myocytes of doxorubicin-treated rats had larger nuclei and/or a larger quantity of AgNORs that were either dispersed in a number of small dots or clustered in rounded, rod-shaped, or tortuous large structures. AgNOR alterations may reflect a defect of nucleolar association leading to an impairment of protein synthesis that could be involved in doxorubicin cardiotoxicity.