Stereological study of the zona fasciculata of the adrenal cortex in stress situations (hypothermia, catabolism)

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Quantitative cytoarchitecture of the liver of the shrew Crocidura russula (fam. Soricidae). Ultrastructural and morphometric comparison with rat liver

The livers of two groups of the shrew Crocidura russula, kept under standardized physiological conditions, were investigated with electron microscopy and morphometry. The adaptations to the extremely high basal metabolism of these small mammals are reflected in the architectural characteristics of the hapatocytes, which, in comparison with those of the rat, show a smaller cell volume of the mononuclear hepatocytes (3,800 micrometers3), and increased number of cells per cm3 of liver tissue (250 X 10(6)), and a relative larger liver volume (4.85 ml per 100 g body weight). The ground substance is reduced by the other cell compartments to 4%. The volume density of the glycogen differs from 5-15% and the variation of the SER is from 10-20%. The RER (constant at about 35%) and the mitochondria (around 30%) form the main part of the cytoplasm of the hepatocyte. The mean volume of individual mitochondria amounts to 2.5 micrometers3. The chrondriome in the cell shows important numerical-volumetrical transformations, i.e, an increase in the individual volume of mitochondria correlating with a decrease in the number of the mitochondria per volume unit and vice versa. The adaptations to the high basal metabolism and the special conditions of life (short phases of activity, long resting times) are considered in relation to the possible functional activity of the megamitochondria.