# The Effects of ACTH and Dexamethasone on the Transcriptomic Profile of the Rat Adrenal Gland: An In Vivo Study

## TL;DR

This study explores how ACTH and Dexamethasone affect gene activity in rat adrenal glands, revealing distinct responses to acute and prolonged stress signals.

## Contribution

The study identifies distinct transcriptional programs triggered by acute ACTH stimulation versus prolonged ACTH exposure and Dexamethasone treatment in rat adrenal glands.

## Key findings

- Acute ACTH exposure activates immediate-early genes and stress-related pathways like cAMP-PKA-CREB signaling.
- Prolonged ACTH exposure suppresses mitochondrial genes and activates epigenetic repression mechanisms.
- Dexamethasone inhibits cholesterol metabolism pathways via suppression of the SREBP pathway.

## Abstract

The hypothalamic–pituitary–adrenal (HPA) axis plays a pivotal role in regulating stress responses through ACTH-stimulated glucocorticoid production. The transcriptional programmes underlying temporal adaptation to prolonged ACTH exposure and glucocorticoid feedback remain incompletely characterized. Adult male Wistar rats were subjected to acute ACTH stimulation (single injection, 1 h) to elicit an immediate transcriptional response, prolonged ACTH exposure (three injections over 36 h) as a repeated exposure, or Dexamethasone treatment (three injections over 36 h). Plasma corticosterone levels were subsequently measured using an enzyme-linked immunosorbent assay (ELISA). The adrenal transcriptome profiling was performed using Affymetrix arrays. Differentially expressed genes (DEGs; |fold change| ≥ 1.8, adjusted p < 0.05) were analyzed using limma, followed by pathway and network analyses. Acute ACTH exposure resulted in the induction of 569 DEGs (357 upregulated), including immediate-early genes (Nr4a family, AP-1 factors), cAMP-PKA-CREB signalling components, and heat shock proteins. Prolonged ACTH resulted in 98 DEGs (predominantly downregulated), including the suppression of mitochondrial genes and upregulation of Polycomb repressive complex 2 components, suggesting epigenetic transcriptional attenuation. Dexamethasone treatment yielded 75 DEGs with selective suppression of SREBP-mediated cholesterol biosynthesis and uptake pathways. Twelve genes were downregulated by both prolonged ACTH and Dexamethasone, including sterol metabolism and interferon-stimulated genes. Acute and prolonged ACTH exposure engage distinct transcriptional programmes. Acute stimulation activates immediate-early genes and stress responses, while prolonged exposure suppresses mitochondrial gene expression through transcriptional dampening mechanisms. Dexamethasone is associated with the inhibition of cholesterol metabolism via SREBP pathway suppression. These findings illuminate HPA axis adaptation and glucocorticoid-induced adrenal suppression.