Effects of hypophysectomy and in vivo administration of ACTH or dexamethasone on the level of ACTH receptor mRNA in adrenal glands and adipose tissues of mice

Abstract

Objective: In rodents, ACTH induces steroidogenesis in the adrenal cortex and also lipolysis in adipose tissues via the sole specific receptor for ACTH. Up-regulation of the ACTH receptor (ACTH-R) mRNA by ACTH was found to be evident in adrenocortical cells. However, a role of in vivo ACTH on ACTH-R mRNA expression in the adrenal cortex is not well understood. In addition, so far less attention has been also paid to the regulation of ACTH-R expression in adipose tissues. We investigated the effects of hypophysectomy and in vivo administration of ACTH or dexamethasone on the level of ACTH-R mRNA in the adrenal gland and adipose tissues of mice.

Methods: ACTH mRNA in the adrenal glands and epididymal adipose tissues of mice sacrificed 10 days after hypophysectomy or sham operation, and 24 hours after ACTH-Z (2 IU i.m.) or physiological saline solution (PSS) injection, and also 3-days after dexamethasone (300 microg/day i.m.) or PSS administration was analysed by Northern blot, and intensities of autoradiographic bands were quantified.

Results: In the adrenal gland, in vivo administration of ACTH-Z significantly increased the level of ACTH-R mRNA to 342% of control values, but in vivo administration of dexamethasone or hypophysectomy induced no significant alteration of ACTH-R mRNA. In adipose tissues, these conditions did not significantly alter the level of ACTH-R mRNA.

Conclusion: Low circulating ACTH may not be a substantial factor for ACTH-R gene expression in the adrenal gland, but a high level of in vivo ACTH dose up-regulated the expression. A different regulation of ACTH-R gene expression exists in the adrenal cortex and adipose tissues of mice.