Angiotensin II type 2 receptor counter-regulates type 1 receptor in catecholamine synthesis in cultured porcine adrenal medullary chromaffin cells

Cardiovascular effect of inflammation and nonsteroidal anti-inflammatory drugs on renin-angiotensin system in experimental arthritis

A co-morbidity of inflammatory conditions is increased cardio-renal risks. Additionally, nonsteroidal anti-inflammatory drugs (NSAIDs) which are used to treat pain and inflammation are also associated with increase in such risks. We hypothesized that inflammation and NSAIDs impose the cardio-renal risk through the activation of the renin-angiotensin-system (RAS), a regulating pathway of the renal and cardiovascular homeostasis. We investigated the effect of adjuvant arthritis and NSAIDs on the RAS. Western blotting and ELISA were used to measure the RAS components. Inflammation caused significant imbalances in the cardiac and renal angiotensin converting enzymes, their biologically active angiotensin peptides (AngII and Ang1-7) and the target proteins involved in the peptide-receptor binding (AngII type 1 and type 2, and Ang1-7 receptor, Mas) toward cardio-renal toxicity. However, 7 days treatment of arthritic animals with NSAIDs (rofecoxib, meloxicam, celecoxib and flurbiprofen) restored the constitutive balances, perhaps due to their anti-inflammatory properties. Inflammation exerts its cardio-renal effects by causing imbalance in the RAS. NSAIDs through their anti-inflammatory effect restore this imbalance. Thus, mechanisms other than imbalances in the RAS may be involved in the NSAIDs cardiotoxicity.

Regulation of nonclassical renin-angiotensin system receptor gene expression in the adrenal medulla by acute and repeated immobilization stress

The involvement of the nonclassical renin-angiotensin system (RAS) in the adrenomedullary response to stress is unclear. Therefore, we examined basal and immobilization stress (IMO)-triggered changes in gene expression of the classical and nonclassical RAS receptors in the rat adrenal medulla, specifically the angiotensin II type 2 (AT2) and type 4 (AT4) receptors, (pro)renin receptor [(P)RR], and Mas receptor (MasR). All RAS receptors were identified, with AT2 receptor mRNA levels being the most abundant, followed by the (P)RR, AT1A receptor, AT4 receptor, and MasR. Following a single IMO, AT2 and AT4 receptor mRNA levels decreased by 90 and 50%, respectively. Their mRNA levels were also transiently decreased by repeated IMO. MasR mRNA levels displayed a 75% transient decrease as well. Conversely, (P)RR mRNA levels were increased by 50% following single or repeated IMO. Because of its abundance, the function of the (P)RR was explored in PC-12 cells. Prorenin activation of the (P)RR increased phosphorylation of extracellular signal-regulated kinase 1/2 and tyrosine hydroxylase at Ser31, likely increasing its enzymatic activity and catecholamine biosynthesis. Together, the broad and dynamic changes in gene expression of the nonclassical RAS receptors implicate their role in the intricate response of the adrenomedullary catecholaminergic system to stress.

Angiotensin II type 2 receptor signaling affects dopamine levels in the brain and prevents binge eating disorder

INTRODUCTION

Binge eating disorder (BED) is associated with dopaminergic activation as food reward, resulting in metabolism-related disorders. Stimulation of angiotensin type 2 (AT2) receptor is reported to inhibit dopamine synthesis. We investigated the possible roles of AT2 receptor-mediated dopamine regulation in the pathogenesis of BED.

MATERIALS AND METHODS

Male C57BL/6 mice, type 2 diabetic (KKAy) mice and AT2 receptor-null (AT2KO) mice at eight weeks old were treated with AT2 receptor agonist, compound 21 (C21) or saline for two weeks. Mice were subjected to fasting for two days followed by re-feeding for seven days.

RESULTS

Treatment with C21 attenuated the rebound proportion of body weight, food intake and water intake in KKAy mice, but not in C57BL/6 and AT2KO mice. Dopamine concentration in the striatum was further increased by fasting in KKAy and AT2KO mice. Administration of C21 significantly attenuated this fasting-induced increase in dopamine level only in KKAy mice. Dopamine receptor D1, D2 expression in the substantia nigra were markedly lower in KKAy mice compared with C57BL/6 mice, while administration of C21 increased their expression in KKAy mice.

CONCLUSIONS

Our study suggests that AT2 receptor stimulation may be a new therapeutic approach to improve eating disorder associated with dopamine resistance.

Bradykinin B2 receptor in the adrenal medulla of male rats and mice: glucocorticoid-dependent increase with immobilization stress

Bradykinin, acting via the bradykinin B2 receptor (B2R), is a potent stimulator of adrenomedullary catecholamine biosynthesis and release and likely plays an important role in the adrenomedullary stress response. However, the effects of stress on the expression of this receptor in the adrenal medulla are currently unclear. Here, we examined the changes in adrenomedullary B2R gene expression in male rats in response to single (1 time) and repeated (6 times) exposure to 2 hours immobilization stress (IMO). Immediately after 1 or 6 times IMO, B2R mRNA levels were increased by 9-fold and 7-fold, respectively, and returned to unstressed control levels 3 hours later. This large, but transient, increase in mRNA elicited a doubling of protein levels 3 hours after the stress exposure. Next, the role of the hypothalamic-pituitary-adrenocortical axis in the stress-induced upregulation of B2R gene expression was examined. Treatment with endogenous (corticosterone) and synthetic (dexamethasone) glucocorticoids dose-dependently increased B2R mRNA levels in adrenomedullary-derived PC12 cells. Furthermore, cortisol supplementation at levels mimicking stress exposure elevated B2R mRNA levels in the adrenal medulla of hypophysectomized rats. In response to 1 exposure to IMO, the stress-triggered rise in plasma corticosterone and adrenomedullary B2R mRNA levels was attenuated in CRH-knockout mice and absent in pharmacologically adrenalectomized rats, indicating a requirement for glucocorticoids in the upregulation of B2R gene expression with stress. Overall, the increase in B2R gene expression in response to the stress-triggered rise in glucocorticoids likely enhances catecholamine biosynthesis and release and may serve as an adaptive response of the adrenomedullary catecholaminergic system to stress.

Regulation of angiotensin II type 2 receptor gene expression in the adrenal medulla by acute and repeated immobilization stress

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 (AT(1A)) and type 2 (AT(2)) receptors in rat adrenal medulla in response to immobilization stress (IMO). AT(2) receptor mRNA levels decreased immediately after a single 2-h IMO. Repeated IMO also decreased AT(2) receptor mRNA levels, but the decline was more transient. AT(1A) 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 (AT(1) receptor antagonist) or with CGP42112 (AT(2) receptor agonist) treatment. Involvement of stress-triggered activation of the hypothalamic-pituitary-adrenocortical or sympathoadrenal axis in AT(2) receptor downregulation was examined. Cultured cells treated with the synthetic glucocorticoid dexamethasone displayed a transcriptionally mediated decrease in AT(2) receptor mRNA levels. However, glucocorticoids are not required for the immediate stress-triggered decrease in AT(2) 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 AT(2) receptor gene expression and may mediate this response. Overall, the effects of stress on adrenomedullary AT(1A) and AT(2) receptor expression may contribute to allostatic changes, such as regulation of catecholamine biosynthesis.

Apelin secretion and expression of apelin receptors in 3T3-L1 adipocytes are differentially regulated by angiotensin type 1 and type 2 receptors

Adipocytes play pivotal roles in regulating metabolism through secretion of a variety of adipokines, which in turn is regulated by other metabolic factors (e.g., insulin). Understanding the regulations of adipokine secretion is important because adipokines are implicated with metabolic disorders, such as, obesity and diabetes mellitus. Here, we investigated the regulatory roles of angiotensin II (AngII) on the secretion of apelin in 3T3-L1 adipocytes, and distinct signaling pathways mediated by AngII receptor type 1 (AT₁) and type 2 (AT₂) were revealed. It was found that activation of AT₁ receptors stimulates apelin secretion in Ca²⁺, protein kinase C, and MAPK kinase dependent ways while activation of AT₂ receptors inhibits apelin secretion through cAMP and cGMP dependent pathways. Furthermore, we demonstrate that the expression of apelin receptor (APJ) is also similarly regulated by AT₁ and AT₂ receptors. Finally, a detailed AngII signaling map is proposed.

Pregnancy and Ovarian Steroid Regulation of Angiotensin II Type 1 and Type 2 Receptor Expression in Ovine Uterine Artery Endothelium and Vascular Smooth Muscle

Although pregnancy is clearly associated with refractoriness to infused angiotensin II (AII) in the uteroplacental unit, there is still dispute over the mechanism by which angiotensin type 1 and type 2 receptors (AT1R and AT2R) may mediate this response in the uterine artery. This is in large part due to incomplete knowledge of levels of AT1R and AT2R expression and function in uterine artery endothelium (UA Endo) in the nonpregnant (NP) and pregnant (P) states, combined with the disagreement on whether AII may act through release of adrenomedullary catecholamines. The authors have previously described an increase in AT1R in UA Endo but not UA vascular smooth muscle (VSM) during pregnancy as compared to the nonpregnant intact ewe. Herein they report that the pregnancy-associated increase in AT(1)R expression in UA Endo is regulated by ovarian steroids. Using a recently developed antibody to AT2R, the authors now show there is no change in AT2R in UA Endo or VSM associated with ovarian function, and although AT2R is not changed in UA Endo by pregnancy, there is a significant decrease observed in UA VSM at that time. The authors also examined changes in receptors in UA Endo and VSM in estrogen (E2beta)-primed ewes in view of the common use of this model as a control for physiologic studies. In contrast to their findings in nonprimed nonpregnant or pregnant animals, the authors observed a significant increase in both AT1R and AT2R in UA Endo in response to the supraphysiologic priming with E2beta. In order to address the possible functionality of AT1R or AT2R in UA Endo, the authors used the uterine artery endothelial cell (UAEC) model of UA endothelial cells maintained in culture to passage 4. Differences in expression of AT1R or AT2R were normalized at passage 4 in P-UAECs and NP-UAECs. Treatment with AII activated phospholipase C (PLC) in both NP- and P-UAECs but signaling through the extracellular signal-regulated kinase (ERK) pathway was dramatically enhanced in P-UAECs compared to NP-UAECs. Surprisingly, both phosphoinositol turnover and ERK2 phosphorylation responses failed to display the expected dose-responses. Inhibition of AII-stimulated ERK2 phosphorylation with antagonists DUP 753 (AT1R, 10 microM) and PD 123319 (AT2R, 10 microM) failed to selectively inhibit ERK2 phosphorylation. The authors conclude that (a) the net effect of pregnancy may be an increase in the AT1R/AT2R ratio in both UA Endo and VSM but through apparently distinct mechanisms, (b) the ovariectomized animal model is similar to the luteal state for AT1R and AT2R expression, while the E2beta-primed model does not resemble the nonpregnant or pregnant state, and (c) there is a real possibility that AII may mediate its effects either through a complex AT1R-AT2R interaction or via an as-yet unidentified non-AT1, non-AT2 receptor.

Effect of age on angiotensin II-mediated downregulation of adrenomedullary catecholamine biosynthetic enzymes

Expression of catecholamine biosynthesizing enzymes, tyrosine hydroxylase (TH) and dopamine beta hydroxylase (DbetaH) increase with age in the adrenal medulla, however, the underlying mechanisms are unclear. In the present study, we examined the effect of peripheral angiotensin II (AngII) on the expression of TH and DbetaH, in the adrenal medulla of young (6 mo) and old (23 mo) Fischer-344 rats. Saline or AngII (230 ng/kg/min sc) was infused for 3 days using osmotic minipumps. Adrenomedullary TH and DbetaH mRNA levels increased significantly with age, and while AngII reduced the expression of these enzymes in young animals, it had no such effect in the old animals. Neuropeptide Y (NPY), which is co-released with catecholamines in the adrenal medulla and stimulates the synthesis of TH and DbetaH, was also upregulated with age and downregulated in response to AngII in young rats. However, in the old animals, the already elevated NPY expression remained unchanged following AngII treatment. This data indicate that the hypertensive effect of peripheral AngII is compensated by an inhibition of adrenomedullary catecholamine biosynthesis in young animals, but this mechanism is impaired in senescence, potentially contributing to the age-related increase in catecholamine biosynthesis.

Effect of caveolin-1 scaffolding peptide and 17β-estradiol on intracellular Ca2+ kinetics evoked by angiotensin II in human vascular smooth muscle cells

Caveolae are identifiable plasma membrane invaginations. The main structural proteins of caveolae are the caveolins. There are three caveolins expressed in mammals, designated Cav-1, Cav-2, and Cav-3. It has been postulated that Cav-1 acts as a scaffold protein for signaling proteins; these include ion channels, enzymes, and other ligand receptors like membrane-associated estrogen receptor (ER)α or ERβ. Caveolae-associated membrane proteins are involved in regulating some of the rapid estrogenic effects of 17β-estradiol. One important system related to the activity of ERα and caveolae is the renin-angiotensin system. Angiotensin II (ANG II) has numerous actions in vascular smooth muscle, including modulation of vasomotor tone, cell growth, apoptosis, phosphatidylinositol 3-kinase (PI3K)/Akt activation, and others. Many proteins associated with caveolae are in close relation with the scaffolding domain of Cav-1 (82–101 amino acid residues). It has been proposed that this peptide may acts as a kinase inhibitor. Therefore, to explore the ability of Cav-1 scaffolding peptide (CSP-1) to regulate ANG II function and analyze the relationship between ERα and ANG II type 1 and 2 (AT1 and AT2) receptors, we decided to study the effects of CSP-1 on ANG II-induced intracellular Ca2+ kinetics and the effect of 17β-estradiol on this modulation using human smooth muscle cells in culture, intracellular Ca2+ concentration measurements, immuno- and double-immunocytochemistry confocal analysis of receptor expression, immunoblot analysis, and immunocoprecipitation assays to demonstrate coexpression. We hypothesized that CSP-1 inhibits ANG II-mediated increases in intracellular Ca2+ concentrations by interfering with intracellular signaling including the PI3K/Akt pathway. We also hypothesize that AT2 receptors associate with Cav-1. Our results show that there is a close association of AT1, AT2, and ERα with Cav-1 in human arterial smooth muscle cells in culture. CSP-1 inhibits ANG II-induced intracellular signaling.

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

We examined if life-long mild caloric restriction (CR) alone or with voluntary exercise prevents the age-related changes in catecholamine biosynthetic enzyme levels in the adrenal medulla and hypothalamus. Ten-week-old Fisher-344 rats were assigned to: sedentary; sedentary+8% CR; or 8% CR+wheel running. Rats were euthanized at 6 or 24 months of age. Tyrosine hydroxylase (TH) mRNA expression was 4.4-fold higher in the adrenal medullae and 60% lower in the hypothalamus of old sedentary rats compared to young (p<0.01). Life-long CR reduced the age-related increase in adrenomedullary TH by 50% (p<0.05), and completely reversed the changes in hypothalamic TH. Voluntary exercise, however, had no additional effect over CR. Since angiotensin II is involved in the regulation of catecholamine biosynthesis, we examined the expressions of angiotensin II receptor subtypes in the adrenal medulla. AT(1) protein levels were 2.8-fold higher in the old animals compared to young (p<0.01), and while AT(1) levels were unaffected by CR alone, CR+wheel running decreased AT(1) levels by 50% (p<0.01). AT(2) levels did not change with age, however CR+wheel running increased its level by 42% (p<0.05). These data indicate that a small decrease in daily food intake can avert age-related changes in catecholamine biosynthetic enzyme levels in the adrenal medulla and hypothalamus, possibly through affecting angiotensin II signaling.

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

To discover regulatory pathways dependent on midkine (Mk the gene, MK the protein) signaling, we compared the transcriptional profiles of aortae obtained from Mk -/- and wild type (WT, +/+) mice; the comparison demonstrated an extraordinary high level expression of tyrosine hydroxylase (12-fold), the rate-limiting enzyme in catecholamine biosynthesis, DOPA decarboxylase (73-fold), and dopamine beta-hydroxylase (75-fold) in aortae of Mk -/- mice compared with aortae of WT (+/+) mice. Phenylethanolamine-N-methyltransferase, the enzyme catalyzing the conversion of norepinephrine into epinephrine, was not detected in either Mk -/- and WT (+/+) mouse aorta. The protein levels of tyrosine hydroxylase, DOPA decarboxylase and dopamine beta-hydroxylase confirmed the analysis of the transcriptional profiles. Surprisingly, MK failed to regulate the enzymes of the catecholamine biosynthesis pathway in 10 other tissues studied. Furthermore, the expression levels of the enzymes of catecholamine biosynthesis in aortae of Mk -/- mice were effectively the same as those in aortae of Pleiotrophin (Ptn the gene, PTN the protein) genetically deficient (Ptn -/-) mice when compared with WT (+/+) mice. The remarkable increases in levels of expression of tyrosine hydroxylase, DOPA decarboxylase and dopamine beta-hydroxylase suggest that MK together with PTN are very important regulators of the catecholamine pathway in mouse aorta and may critically regulate catecholamine biosynthesis and function in inflammatory and the other pathological conditions in which Mk or Ptn are upregulated. The data also establish that norepinephrine is effectively the only catecholamine synthesized in mouse aorta.

Angiotensin II AT1and AT2Receptor Types Regulate Basal and Stress-Induced Adrenomedullary Catecholamine Production through Transcriptional Regulation of Tyrosine Hydroxylase

The sympathoadrenal response to stress includes a profound increase in adrenomedullary catecholamine synthesis driven by stimulation of tyrosine hydroxylase (TH) transcription. We studied the role of Angiotensin II type 1 and 2 (AT(1) and AT(2)) receptors during isolation stress, and under basal conditions. Pretreatment of rats with the AT(1) receptor antagonist candesartan for 14 days prior to isolation completely prevented the stress-induced stimulation of catecholamine synthesis, decreasing tyrosine hydroxylase transcription by preventing the expression of the transcriptional factor, Fos-related antigen 2 (Fra-2). In addition, AT(1) receptor antagonism prevented the stress-induced increase in adrenomedullary AT(2) receptor binding and protein. Treatment of non-stressed, grouped animals under basal conditions with the AT(1) receptor or with PD 123319, an AT(2) receptor antagonist, decreased the adrenomedullary norepinephrine (NE) content and TH transcription. While AT(1) receptor antagonism decreased the levels of Fra-2 and the phosphorylated forms of cAMP responsive element binding protein (pCREB) and EKR2 (p-ERK2, phosphor-p42 MAP kinase), the AT(2) antagonist decreased Fra-2 with no change in the phosphorylation of CREB or EKR2. Our results demonstrate that both adrenomedullary AT(1) and AT(2) receptor types maintain and promote the adrenomedullary catecholamine synthesis and the transcriptional regulation of TH. Instead of opposing effects, however, our results indicate a complex synergistic regulation between the AT(1) and AT(2) receptor types.

Angiotensin-(1–7) inhibits the angiotensin II-enhanced norepinephrine release in coarcted hypertensive rats

Since it has been suggested that angiotensin (Ang) (1-7) functions as an antihypertensive peptide, we studied its effect on the Ang II-enhanced norepinephrine (NE) release evoked by K+ in hypothalami isolated from aortic coarcted hypertensive (CH) rats. The endogenous NE stores were labeled by incubation of the tissues with 3H-NE during 30 min, and after 90 min of washing, they were incubated in Krebs solution containing 25 mM KCl in the absence or presence of the peptides. Ang-(1-7) not only diminished the K+-evoked NE release from hypothalami of CH rats, but also blocked the Ang II-enhanced NE release induced by K+. Ang-(1-7) blocking action on the Ang II response was prevented by [D-Ala7]Ang-(1-7), an Ang-(1-7) specific antagonist, by PD 123319, an AT2-receptor antagonist, and by Hoe 140, a B2 receptor antagonist. Ang-(1-7) inhibitory effect on the Ang II facilitatory effect on K+-stimulated NE release disappeared in the presence of Nomega-nitro-L-arginine methylester and was restored by L-arginine. Our present results suggest that Ang-(1-7) may contribute to blood pressure regulation by blocking Ang II actions on NE release at the central level. This inhibitory effect is a nitric oxide-mediated mechanism involving AT2 receptors and/or Ang-(1-7) specific receptors and local bradykinin generation.

Angiotensin II AT2 receptor subtype: an uprising frontier in cardiovascular disease?

The renin-angiotensin system (RAS) plays a pivotal role in the regulation of fluid, electrolyte balance and blood pressure, and is a modulator of cellular growth and proliferation. Biological actions of RAS are linked to the binding of the effector molecule, angiotensin II (AngII), to specific membrane receptors, mostly the AT1 subtype and, to a lesser extent, other subtypes. Following the identification and characterization of the AT2 subtype receptor, it has been proposed that a complex interaction between AngII and its receptors may play an important role in the effects of RAS. In this paper current information on AngII subtype receptors--their structure, regulation and intracellular signalling--are reviewed, with a particular emphasis on the potential relevance for cardiovascular pathophysiology. In addition, we discuss modulation of expression of the AT2 receptor and its interaction with the AT1 receptor subtype, as well as the potential effects of this receptor on blood pressure regulation. A better understanding of the integrated effects of the AngII subtype receptors may help to elucidate the function of the RAS, as well as their participation in the mechanisms of cardiovascular disease and attendant therapeutic implications.

Angiotensin II AT(1) and AT(2) receptors contribute to maintain basal adrenomedullary norepinephrine synthesis and tyrosine hydroxylase transcription

Angiotensin II (Ang II) AT(1) 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 AT(2) type. We asked the question whether AT(1) and AT(2) receptors regulate basal catecholamine synthesis. Long-term AT(1) receptor blockade decreased adrenomedullary AT(1) receptor binding, AT(2) receptor binding and AT(2) 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 AT(2) receptor blockade decreased AT(2) receptor binding, TH mRNA, NE content and Fra-2 protein, although not affecting AT(1) receptor binding or receptor protein, pCREB or ERK2. Angiotensin II colocalized with AT(1) and AT(2) receptors in ganglion cell bodies. AT(2) receptors were clearly localized to many, but not all, chromaffin cells. Our data support the hypothesis of an AT(1)/AT(2) 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 AT(1) and AT(2) receptors involve the Fos-related antigen Fra-2, AT(1) receptor transcriptional effects include pCREB and ERK2, indicating common as well as different regulatory mechanisms for each receptor type.

Upregulation of catecholamine biosynthetic enzymes by nitric oxide

Nitric oxide (NO) is recognized as an essential intercellular messenger in central and peripheral nervous systems. In the present study, whether NO exerts effects on catecholamine (CA) biosynthetic enzymes was determined in primary cultured bovine chromaffin cells. The NO generators sodium nitroprusside (SNP) and S-nitroso-N-acetyl-D,L-penicillamine, in a dose-dependent manner, upregulated transcript levels of tyrosine hydroxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase, accompanied by long-term increases in their enzyme activities and the intracellular CA levels. The SNP effect was diminished by co-treatment with LY83583, an inhibitor of soluble guanylate cyclase, or H-8, a cyclic GMP (cGMP)-dependent protein kinase inhibitor. Co-treatment with 8-Br-cGMP did not increase further the expression of these enzyme genes induced by SNP. Taken together, the data suggest that NO leads to long-term upregulation of the CA system via induction of the genes involved and that this is mediated by cGMP-dependent signaling pathway.