Introduction: Humans with glucocorticoid receptor (GR) deficiency and global heterozygous GR knockout (GR+/−) show compensatory activation of the hypothalamic-pituitary-adrenal axis, resulting in salt-sensitive hypertension due to increased mineralocorticoid activity. Previous studies suggest renal mechanisms, including changes in cell proliferation, gene expression and electrolyte transport, may contribute to this phenotype but underlying adaptive adrenal responses have yet to be investigated.
Methods: Bromodeoxyuridine (BrdU) infusion was used to label proliferating cells and apoptosis was assessed by TUNEL staining. Cell size and cell proliferation were quantified in fixed adrenal sections from GR+/− mice and wild-type littermate (WT) controls using Image J software. Zonal expression of aldosterone synthase (AS; Cyp11b2) and 11-beta hydroxylase (11β-OH; Cyp11b1) was assessed using immunofluorescence.
Results: Compared to WT adrenals, the outer zona fasciculata (OZF) cells of GR+/− adrenals were larger (P=0.0001), medulla cells were smaller (P=0.025) and zona glomerulosa (ZG) cells appeared unaffected. Irrespective of genotype, BrdU+ve nuclei were more abundant in the outer cortex. However, the adrenal cortex of GR+/− mice (P<0.05) had fewer BrdU-labelled cells and the distribution of labelled cells was shifted markedly (P<0.001) away from the ZG towards the medulla. Dual immunofluorescent staining for BrdU and either AS (expressed only in ZG cells) or 11β-OH (expressed only in ZF cells) showed that, in GR+/− adrenals, AS may be increased but not in association with proliferating cells. Nearly all BrdU+ve cells expressed 11β-OH. Tunel staining showed no difference in apoptosis between genotypes.
Conclusion: Impaired negative feedback of the hypothalamo-pituitary-adrenal axis in GR+/− mice causes ACTH-dependent hypertrophy but not hyperplasia of the glucocorticoid-synthesizing zona fasciculata cells of the adrenal cortex. Although adrenal aldosterone synthesis may be increased in GR+/− mice, it is not yet clear that this is sufficient to explain mineralocorticoid-dependent hypertension. The distribution of BrdU labelled nuclei may indicate altered adrenocortical cell turnover.