Allometric analysis of organ weights: II. Beagle dogs

Circumstances, Descriptive Characteristics, and Pathologic Findings in Dogs Suspected of Starving

The authors reviewed the case circumstances, population characteristics, gross, and histopathologic findings in 40 cases of emaciated dogs with a suspected diagnosis of starvation. The dogs’ estimated age ranged from 3 months to geriatric. Nineteen breeds were represented, including small-breed ( n = 11), large-breed ( n = 13), and pit bull–type ( n = 16) dogs. The median body condition score was 1 out of 9 (Purina scale). Various diseases were identified as the cause of death in 7 dogs, while the cause of death in the other 33 dogs was starvation due to exogenous causes (SEC). Circumstances associated exclusively with SEC included being found in a vacated residence and death during temperature extremes or severe weather. Dogs with SEC did not differ significantly from diseased dogs in body condition score, sex, neuter status, or breed category (small, large, or pit bull type). Gross findings associated exclusively with SEC included severe hair matting and traumatic injuries. Diseased dogs had an empty stomach significantly more often than SEC dogs, which frequently had food and/or foreign material in the stomach. In 5 of the 7 cases where disease was the cause of death, disease involved the gastrointestinal tract. Gross and histopathologic changes commonly found in SEC and diseased dogs included the following: gross loss of muscle mass and absence of subcuticular fat; serous atrophy of omental, perirenal, epicardial, and bone marrow fat; atrophy of the liver, skin, thyroid gland, and testicle; gastric mucosal petechiae and ecchymoses; melena; and splenic hemosiderophages.

Anatomical and physiological basis for the allometric scaling of cisplatin clearance in dogs

Cisplatin is a platinum-containing cytotoxic drug indicated for the treatment of solid tumors in veterinary and human patients. Several of the algorithms used to standardize the doses of cytotoxic drugs utilize allometry, or the nonproportional relationships between anatomical and physiological variables, but the underlying basis for these relationships is poorly understood. The objective of this proof of concept study was to determine whether allometric equations explain the relationships between body weight, kidney weight, renal physiology, and clearance of a model, renally cleared anticancer agent in dogs. Postmortem body, kidney, and heart weights were collected from 364 dogs (127 juveniles and 237 adults, including 51 dogs ≥ 8 years of age). Renal physiological and cisplatin pharmacokinetic studies were conducted in ten intact male dogs including two juvenile and eight adult dogs (4-55 kg). Glomerular filtration rate (GFR), effective renal plasma flow, effective renal blood flow, renal cisplatin clearance, and total cisplatin clearance were allometrically related to body weight with powers of 0.75, 0.59, 0.61, 0.71, and 0.70, respectively. The similar values of these diverse mass exponents suggest a common underlying basis for the allometry of kidney size, renal physiology, and renal drug handling.

Effects of four-week feed restriction on toxicological parameters in beagle dogs

This study was conducted to examine any changes caused by feed restriction in dogs to contribute to safety evaluation in toxicity studies. Two male 7-month-old beagle dogs/group were fed 300 (control), 150 (50% of control), or 70 g/animal of diet daily (23% of control) for 4 weeks. Effects of feed restriction, except for clinical signs, were noted depending on the feed dosage in almost all examinations. The principal outcomes were: decreased body weight and water consumption, ECG changes (decreased heart rate and prolonged QTc), and hematopoietic and lymphopoietic suppression (decreased reticulocyte ratio or white blood cell count in hematology, decreased nucleated cell count in bone marrow, decreased erythroid parameters in myelography, and hypocellularity of bone marrow and thymic atrophy in histopathology). In addition, some changes were noted in urinalysis (decreased urine volume and sodium and potassium excretion), blood chemistry (decreased ALP and inorganic phosphorus and increased creatinine), organ weights, and gastric histopathology. These results provide important reference data for distinguishing the primary effects of test compounds from secondary effects of decreased food consumption in toxicity studies in beagle dogs.

Postnatal growth considerations for PBPK modeling

A physiologically based pharmacokinetic (PBPK) model and Windows-based program (called PostNatal) was developed that focuses on postnatal growth, from birth through adulthood, using appropriate growth curves for each species and gender. Postnatal growth algorithms relating organs/tissues weights with total body weight for male and female humans, dogs, rats, and mice are an integral part of the software and are utilized to assign the appropriate weight and blood flow for each of 22 organs/tissues for each simulation. Upper limits of body weight were chosen that reflect the available data used to define the algorithms; above these limits a set percent body weight was assigned to all organs/tissues.

Age-related variations in the testes and prostate of beagle dogs

Variations in the weight and histology of the testes and prostate of Beagle dogs are described. Data were abstracted from records of toxicity studies performed at the Huntingdon Research Centre during the years 1967--77. A sample of 198 dogs aged between 37 weeks and 7.75 years was analysed. When juvenile dogs are studied, a significant proportion show low testicular weight, incomplete spermatogenesis and immature prostate development after 13-week observation periods. The occurrence of these normal variations may complicate the assessment of gonadal toxicity. In other respects, relatively few spontaneous variations from normal are likely to be encountered in these organs after observation periods lasting up to 2 years. 10% of dogs maintained for a 7-year observation period developed testicular neoplasms and a further 8% showed interstitial cell hyperplasia. Epithelial hyperplasia of the ductus epididymis and benign prostate enlargement were also normal features of the aged male Beagle.

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

It is demonstrated in simulations that, if adjustment for inequality in body weight is to be made by covariance analysis and the comparison is carried out in terms of adjusted means of organ weights thus obtained, the test of significance for an organ weight change can be unbiased, or the chances for detecting spurious effects on organ weights remain at about 5% and the chances for detecting treatment effects are far above the 5% irrespective of differences in body weight. Since the use of relative organ weights frequently violates the unbiasedness, it is concluded that if a treated group differs from the control in body weight the comparison of adjusted means of organ weights by covariance analysis will be far more justifiable than that of relative weights.

Allometric analysis of the atrioventricular heart-valve weights in beagle dogs

A statistical analysis of atrioventricular heart valve weights of 218 beagle dogs was performed. Applying the allometric function, the correlation between body or heart weight and the weights of the mitral valve, tricuspid valve-angular/parietal leaflet and tricuspid valve-septal leaflet could be described statistically. In the age range between 2 and 81 weeks a significant linear, positive correlation was found for all three parts. The mitral valve and the angular and parietal leaflet of the tricuspid valve show a negative allometry or slower growth rate than body or heart, whereas the septal leaflet grows isometrically. Sex differences were not found. The relevance of such data for the evaluation of certain pathological findings is discussed.