Angiotensin II AT1 and AT2 Receptors Contribute to Maintain Basal Adrenomedullary Norepinephrine Synthesis and Tyrosine Hydroxylase Transcription

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Abstract
Angiotensin II (Ang II) AT1 receptors have been proposed to mediate the Ang II-dependent and the stress-stimulated adrenomedullary catecholamine synthesis and release. However, in this tissue, most of the Ang II receptors are of the AT2 type. We asked the question whether AT1 and AT2 receptors regulate basal catecholamine synthesis. Long-term AT1 receptor blockade decreased adrenomedullary AT1 receptor binding, AT2 receptor binding and AT2 receptor protein, rat tyrosine hydroxylase (TH) mRNA, norepinephrine (NE) content, Fos-related antigen 2 (Fra-2) protein, phosphorylated cAMP response element binding protein (pCREB), and ERK2. Long-term AT2 receptor blockade decreased AT2 receptor binding, TH mRNA, NE content and Fra-2 protein, although not affecting AT1 receptor binding or receptor protein, pCREB or ERK2. Angiotensin II colocalized with AT1 and AT2 receptors in ganglion cell bodies. AT2 receptors were clearly localized to many, but not all, chromaffin cells. Our data support the hypothesis of an AT1/AT2 receptor cross-talk in the adrenomedullary ganglion cells, and a role for both receptor types on the selective regulation of basal NE, but not epinephrine formation, and in the regulation of basal TH transcription. Whereas AT1 and AT2 receptors involve the Fos-related antigen Fra-2, AT1 receptor transcriptional effects include pCREB and ERK2, indicating common as well as different regulatory mechanisms for each receptor type.