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.

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.