While the renin–angiotensin system is important for adrenomedullary responses to stress, the involvement of specific angiotensin II (Ang II) receptor subtypes is unclear. We examined gene expression changes of angiotensin II type 1A (AT1A) and type 2 (AT2) receptors in rat adrenal medulla in response to immobilization stress (IMO). AT2 receptor mRNA levels decreased immediately after a single 2-h IMO. Repeated IMO also decreased AT2 receptor mRNA levels, but the decline was more transient. AT1A receptor mRNA levels were unaltered with either single or repeated IMO, although binding was increased following repeated IMO. These effects of stress on Ang II receptor expression may alter catecholamine biosynthesis, as tyrosine hydroxylase and dopamine β-hydroxylase mRNA levels in PC12 cells are decreased with Ang II treatment in the presence of ZD7155 (AT1 receptor antagonist) or with CGP42112 (AT2 receptor agonist) treatment. Involvement of stress-triggered activation of the hypothalamic–pituitary–adrenocortical or sympathoadrenal axis in AT2 receptor downregulation was examined. Cultured cells treated with the synthetic glucocorticoid dexamethasone displayed a transcriptionally mediated decrease in AT2 receptor mRNA levels. However, glucocorticoids are not required for the immediate stress-triggered decrease in AT2 receptor gene expression, as demonstrated in corticotropin-releasing hormone knockout (Crh KO) mice and hypophysectomized rats, although they can regulate basal gene expression. cAMP and pituitary adenylate cyclase-activating polypeptide also reduced AT2 receptor gene expression and may mediate this response. Overall, the effects of stress on adrenomedullary AT1A and AT2 receptor expression may contribute to allostatic changes, such as regulation of catecholamine biosynthesis.
Down-Regulation by cAMP of Angiotensin II Type 2 Receptor Gene Expression in PC12 Cells.