Angiotensin II Type 2 Receptor Counter-Regulates Type 1 Receptor in Catecholamine Synthesis in Cultured Porcine Adrenal Medullary Chromaffin Cells

Abstract

Abstract-We previously showed that CGP 42112 (an angiotensin type 2 [AT 2 ] agonist) markedly reduces catecholamine biosynthesis by decreasing cGMP production mediated by AT 2 , a subtype of Ang II receptor that is dominantly expressed in cultured porcine chromaffin cells. To elucidate the relationship of the 2 types of Ang II receptors, angiotensin type 1 (AT 1 ) and AT 2 , in the synthesis of catecholamine in adrenal medullary cells, we have examined the effect of Ang II plus CV-11974 (an AT 1 antagonist that selectively simulates AT 2 stimulation) and the effect of Ang II plus PD 123319 (an AT 2 antagonist that selectively simulates AT 1 stimulation) on catecholamine synthesis. We found that Ang II reduced cGMP production via AT 2 , in a similar manner to that found with CGP 42112. Stimulation of AT 1 significantly upregulated protein kinase C activity. Tyrosine hydroxylase (TH) is a rate-limiting enzyme involved in the biosynthesis of catecholamine, and this catecholamine synthesis depends both on TH enzyme activity and on the levels of TH protein after TH gene transcription. We found that AT 2 stimulation significantly inhibited TH enzyme activity, whereas AT 1 stimulation significantly upregulated TH enzyme activity. The stimulatory effect of AT 1 was completely inhibited by Ro-32-0432 (a protein kinase C inhibitor) and PD 98059 (a MAP kinase kinase-1 [MEK-1] inhibitor). Pretreatment of cells with either 8-Br-cGMP (a membrane-permeable cGMP analog) or Zaprinast (a phosphodiesterase inhibitor) abolished the inhibitory effect of AT 2 on TH enzyme activity, indicating that the stimulatory effect of AT 2 may be mediated through a reduction in cGMP concentration. Similar to the effect on TH enzyme activity, AT 2 stimulation significantly reduced TH mRNA and protein levels and net catecholamine content below basal levels, whereas AT 1 stimulation increased them. We confirmed these findings by gel mobility shift assay. Our results show that stimulation of AT 2 reduces catecholamine biosynthesis via a decrease in cGMP levels. In contrast, stimulation of AT 1 stimulates catecholamine biosynthesis through activation of PKC. Thus, we conclude that AT 1 and AT 2 have counter-regulatory roles in the synthesis of catecholamine in adrenal medullary chromaffin cells. Key Words: receptors, angiotensin II Ⅲ tyrosine hydroxylase Ⅲ cyclic GMP Ⅲ angiotensin antagonist Ⅲ catecholamines T here are 2 major subtypes of Ang II receptor, type 1 (AT 1 ) and type 2 (AT 2 ). 1 Most of the stimulatory effects of Ang II, such as those on the cardiovascular system and on fluid volume homeostasis, are mediated by AT 1 . AT 1 is linked with activation of phospholipase C and with a subsequent increase in [Ca 2ϩ ] i and protein kinase C (PKC) activity. 1 In contrast, the physiological role of and signal transduction pathways connected with AT 2 are not established. In adults, AT 2 expression is restricted to only a few organs, such as adrenal medulla. 2 It has been shown that stimulation of AT 2 induces a decrease in intracellular cGMP leve...

Angiotensin-(1–7) Inhibitory Mechanism of Norepinephrine Release in Hypertensive Rats

“…22,23 In addition, a counter-regulatory role in catecholamines synthesis by adrenal medullary chromaffin cells has been reported. 24 Supporting this hypothesis, we suggest that AT 2 sites counter-regulate the facilitatory actions of Ang II on NE release at its type 1 receptors because the AT 2 sites are involved in the decreased NE release caused by Ang-(1-7) (present results).…”

Effects of life-long caloric restriction and voluntary exercise on age-related changes in levels of catecholamine biosynthetic enzymes and angiotensin II receptors in the rat adrenal medulla and hypothalamus

“…In spite of this, the selective blockade of AT 1 receptors is sufficient to prevent Ang II-induced catecholamine release in isolated rat adrenal glands (Wong et al, 1990), and longterm inhibition of this receptor subtype decreases both adrenomedullary TH mRNA and norepinephrine content (Armando et al, 2001(Armando et al, , 2004Jezova et al, 2003). In contrast, the role of the dominant AT 2 receptor subtype in the regulation of adrenomedullary catecholamine biosynthesis is not clear, since both activation (Takekoshi et al, 2000(Takekoshi et al, , 2002 and inhibition (Jezova et al, 2003) of this receptor subtype were found to reduce TH expression and catecholamine biosynthesis.…”

“…One explanation might be that the effects of exercise-induced AT 1 downregulation are masked by other beneficial effects of CR. For example, elevated levels of AT 2 receptors caused by CR may have an inhibitory effect on TH and DβH expression by opposing AT 1 signaling (Takekoshi et al, 2000(Takekoshi et al, , 2002, therefore downregulation of AT 1 receptors due to exercise does not have further effects on baseline TH and DβH levels.…”

Midkine is a potent regulator of the catecholamine biosynthesis pathway in mouse aorta

“…Since therapies targeting both AT1 and AT2 receptors and angiotensin converting enzyme have proven successful in regulating the catecholaminergic system in different cardiovascular pathologies, such as hypertension and heart failure (Kawai et al, 2000;Takekoshi et al, 2002), it is suggested that these therapies may be used to target downstream signaling pathways stimulated in common by either MK or PTN in conditions in which expressions of either Mk and Ptn (or both) are elevated, such as systemic sclerosis with diffuse scleroderma (Whitfield et al, 2003). Other functions of Mk expression may be regulated through the catecholamine and/or renin-angiotensin pathways as well; Mk −/− mice have reduced neointima formation in restenosis injury models that is reversible by systemic administration of MK (Horiba et al, 2000) and antisense Mk oligodeoxyribonucleotides suppress neointima formation after injury (Hayashi et al, 2005).…”