Investigations on the turnover of adrenocortical mitochondria. IV. A stereological study of the effect of chronic treatment with ACTH on the size and number of rat zona reticularis mitochondria

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.).

Adrenal morphometry in unilateral and sham adrenalectomized Syracuse high and low avoidance rats

Syracuse high (SHA) and low (SLA) Long-Evans rats, bred for differences in avoidance performance, exhibit dramatic differences in adrenal gland weight. Here we examined adrenal weight and composition (i.e., the size of the medulla, zonae fasciculata/reticularis and glomerulosa) following unilateral adrenalectomy and sham surgery in these strains. Adrenals of SLA animals, regardless of treatment, were heavier and contained larger medullas and cortices than did adrenals of SHA animals. When individual regions were expressed as a percent of total adrenal area, SHA glands (age 31-45 days), although smaller in weight, contained a larger percentage of glomerulosa than did adrenals of SLA animals. Unilateral adrenalectomy produced significant compensatory growth in SHA and SLA animals as indexed by increases in adrenal weight as soon as 7 days after surgery. The adrenal enlargement was the net result of an increase in absolute size of the fasciculata/reticularis (significant 14 days following surgery) and a decrease in the absolute size of glomerulosa (significant 7 days following surgery). These results suggest that SHA and SLA adrenal differences may be the result of genetically determined differential pituitary-adrenal activity.

Stereological analysis of the guinea pig adrenal: effects of dexamethasone and ACTH treatment with emphasis on the inner cortex

This paper describes the morphological responses of adult male guinea pig adrenals to dexamethasone (DEX) and adrenocorticotrophic hormone (ACTH), in both qualitative and quantitative terms. Most organelles and inclusions are affected, but their responses often vary in the different cell types examined: zona fasciculata externa and interna, and zona reticularis. Following DEX the volume of lipid droplets increases in cells of zona fasciculata externa but decreases in zona reticularis; smooth endoplasmic reticulum decreases in fasciculata externa but increases in reticularis. Following ACTH, exactly the opposite occurs. This strongly suggests differing functions for these subcellular entities in each cell type, particularly for the smooth reticulum, as well as for the cells themselves. The volume of the Golgi complex markedly decreases following DEX in all cells but increases only in zona fasciculata interna and zona reticularis following ACTH. These deeper cortical cells are known to secrete at least one sulfated steroid, dehydroepiandrosterone sulfate, and these changes in the Golgi complex strengthen the suggestion that the Golgi plays a role in sulfation of steroids. Mitochondrial volume and number decrease in all cells following DEX, supporting their role in steroidogenesis. Further decreases in their volume, accompanied by increases in their number following ACTH, may be related to a proliferation of mitochondria in response to ACTH. Changes in peroxisome volume and number, following DEX and ACTH, suggest a possible role for these organelles in steroid cell metabolism. Lysosomes decrease in volume in all cells following ACTH. This does not support the recently suggested concept that they play a role in steroid secretion.

Investigations on the turnover of adrenocortical mitochnodria. VII. Effects of ACTH on the half-life of mitochondria from the zona reticularis of the rat adrenal cortex

The half-life of mitochondria from the zona reticularis of the rat adrenal was calculated by determining the radioactivity decay curves of the mitochondrial compartment of 3H-thymidine-injected animals, using autoradiographic methods. ACTH was found to enchance significantly the half-life of the organelles.