Adrenal Gland, Cortex, X-Zone - Atrophy



comment:
The X-zone appears a few days after birth in mice of both sexes and is fully developed by weaning. The X-zone is located at the junction of the cortex and the medulla and is populated by cells with more eosinophilic cytoplasm than those of the zona fasciculata ( Figure 1

Normal regression (involution) of the X-zone in females of many mouse strains, including the B6C3F1 strain, progresses in morphologically distinct stages. The onset of regression begins with vacuolization of scattered constituent cells ( Figure 1


The function of the X-zone is unknown. Its normal development and regression are mediated by gonadal and thyroid hormones, so factors that alter levels of these hormones can affect the X-zone. For example, gonadectomy prolongs the persistence of the X-zone in female mice and prepubertal male mice and can cause the reappearance of the X-zone in postpubertal males. Administration of androgens like testosterone is followed by rapid disappearance of the X-zone in female mice. Administration of certain other chemicals can also affect the X-zone, resulting in asynchronous deviations, such as accelerated regression ( Figure 3




recommendation:
Adrenal cortical X-zone regression is a normal physiologic process, and its various stages are often incidental findings in mice of both sexes and at various ages. Features of normal X-zone regression stages (e.g., vacuolization, degeneration) and its end-stage sequelae (e.g., X-zone collapse, fibrosis, and pigment-cell accumulation) should not be mistaken for pathologic lesions. Thus, physiologic X-zone regression should not be diagnosed when it occurs in a similar, age- and sex-appropriate manner in both the control and treated mice in a given study. Abnormally accelerated (rapid) regression or, conversely, excessively lengthy persistence of the X-zone can be effects of treatment with various chemicals and exogenous hormones. However, in these cases, the X-zone morphology of treated animals will not be distinctive or exhibit pathognomonic pathologic features. Instead, the existence of a toxic effect manifests only as a disparity in the appearance (temporal stage) of the X-zone in treated animals compared with normal, age- and sex-appropriate concurrent study controls. For these reasons, X-zone toxicity in treated animals cannot be diagnosed in isolation but must be evaluated in the context of the physiologic temporal stage occurring in the study controls.references:
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