Aldosterone increases RAMP1 expression in mesenteric arteries from spontaneously hypertensive rats

Vasomotor action of androgens in the mesenteric artery of hypertensive rats. Role of perivascular innervation

Androgens may exert cardiovascular protective actions by regulating the release and function of different vascular factors. In addition, testosterone (TES) and its 5-reduced metabolites, 5α- and 5β-dihydrotestosterone (5α- and 5β-DHT) induce vasorelaxant and hypotensive effects. Furthermore, hypertension has been reported to alter the release and function of the neurotransmitters nitric oxide (NO), calcitonin gene-related peptide (CGRP) and noradrenaline (NA). Since the mesenteric arteries possess a dense perivascular innervation and significantly regulate total peripheral vascular resistance, the objective of this study was to analyze the effect of TES, 5α- and 5β-DHT on the neurogenic release and vasomotor function of NO, CGRP and NA. For this purpose, the superior mesenteric artery from male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats was used to analyze: (i) the effect of androgens (10 nM, incubated for 30 min) on the neurogenic release of NO, CGRP and NA and (ii) the vasoconstrictor-response to NA and the vasodilator responses to the NO donor, sodium nitroprusside (SNP) and exogenous CGRP. The results showed that TES, 5α- or 5β-DHT did not modify the release of NO, CGRP or NA induced by electrical field stimulation (EFS) in the arteries of SHR; however, in the arteries of WKY rats androgens only caused an increase in EFS-induced NO release. Moreover, TES, and especially 5β-DHT, increased the vasodilator response induced by SNP and CGRP in the arteries of SHR. These findings could be contributing to the hypotensive/antihypertensive efficacy of 5β-DHT previously described in conscious SHR and WKY rats, pointing to 5β- DHT as a potential drug for the treatment of hypertension.

Aldosterone Induces Tissue Inhibitor of Metalloproteinases-1 Expression and Further Contributes to Collagen Accumulation

Aldosterone induces myocardial fibrosis. Tissue inhibitor of metalloproteinases-1 (TIMP-1) is a key factor of myocardial fibrosis. This study tested the hypothesis that aldosterone induces TIMP-1 expression and contributes to the fibrotic process. We prospectively enrolled 54 patients with primary aldosteronism, and measured plasma TIMP-1 and echocardiographic parameters. In the cell study, we investigated the possible molecular mechanism by which aldosterone induces TIMP-1 secretion and the effects on collagen accumulation. In the animal study, we measured serum TIMP-1 levels, cardiac TIMP-1 levels, and cardiac structure in an aldosterone infusion mouse model using implantation of aldosterone pellets. In patients with primary aldosteronism, plasma TIMP-1 was correlated with 24-hour urinary aldosterone, left ventricular mass, and impairment of left ventricular diastolic function. In human cardiac fibroblasts, TIMP-1 protein and mRNA expressions were significantly increased by aldosterone through the glucocorticoid receptor/PI3K/Akt/nuclear factor-κB pathway. TIMP-1 small-interfering RNA significantly reduced aldosterone-induced collagen accumulation, and aldosterone did not alter the levels of collagen1a1 or matrix metalloproteinase-1 mRNA. The aldosterone-induced TIMP-1 expression was inversely related to matrix metalloproteinase-1 activity. Furthermore, in the animal model, the serum and cardiac levels of TIMP-1 were significantly elevated in the mice that received aldosterone infusion. This elevation was blocked by RU-486 but not by eplerenone, suggesting that the effect was through glucocorticoid receptors. In a long-term aldosterone infusion model, serum TIMP-1 was associated with serum aldosterone level, cardiac structure, and fibrosis. In conclusion, aldosterone induced TIMP-1 expression in vivo and in vitro. This increased TIMP-1 expression resulted in enhanced collagen accumulation via the suppression of matrix metalloproteinase-1 activity.

Regulation of RAMP expression in diseases

Receptor-activity modifying proteins (RAMPs) belong to a single family of transmembrane proteins. RAMPs determine ligand specificity of G-protein coupled receptors; calcitonin receptor and the calcitonin-receptor like receptor (CLR). To date, three members of RAMP family (RAMP-1, -2, -3) have been identified. The co-expression of RAMP-1 with CLR constitutes the calcitonin gene related peptide receptor whereas the association of the RAMP-2 or RAMP-3 with CLR forms the adrenomedullin (AM) receptor. Alterations in signaling and subcellular distribution of G-protein coupled receptors can be responsible for the regulation of many disease conditions. These changes may be mediated by the different isoforms of RAMPs associated with such receptors. In this chapter, we describe the differential responses associated with upregulation of RAMPs in disease conditions. For instance, the upregulation of all three RAMP isoforms contributes to the cardioprotective effects of the CLR/RAMP ligands. On the other hand, strong evidence exists for the involvement of AM in various cancers and that its action is mediated by the upregulation of RAMP isoforms, RAMP-2 and -3. Though limited, a few studies have been reported on the differential response associated with the upregulation of RAMP in other disease conditions such as sepsis, liver cirrhosis, glomerulonephritis, Type 1 diabetes and Parkinson's disease. Thus, the regulation of RAMP expression is involved in the pathophysiology associated with various diseases.

Cirrhosis decreases vasoconstrictor response to electrical field stimulation in rat mesenteric artery: role of calcitonin gene-related peptide

Our study determines alterations in the vasoconstrictor response elicited by electric field stimulation (EFS) in mesenteric arteries from cirrhotic rats treated with CCl(4), and how calcitonin gene-related peptide (CGRP) participates in this response. Vasoconstriction induced by EFS was analysed in the absence and presence of the CGRP receptor antagonist CGRP(8-37) in arterial segments from control and cirrhotic rats. The vasodilator response to exogenous CGRP was tested in both groups of rats, and the interference of the guanylate cyclase inhibitor ODQ or the K(ATP) channel blocker glibenclamide was analysed only in segments from cirrhotic rats. The vasodilator response to the K(ATP) channel opener pinacidil and to 8-bromo-cyclic GMP was tested. The K(ATP) currents were recorded using the patch-clamp technique. Expression of receptor activity-modifying protein 1 (RAMP1), calcitonin receptor-like receptor, Kir 6.1 and sulfonylurea receptor 2B (SUR2B) was also analysed. Release of CGRP and cGMP was measured. The EFS-elicited vasoconstriction was less in segments from cirrhotic rats. The presence of CGRP(8-37) increased the EFS-induced response only in segments from cirrhotic rats. The CGRP-induced vasodilatation was greater in segments from cirrhotic rats, and was inhibited by ODQ or glibenclamide. Both pinacidil and 8-bromo-cyclic GMP induced a stronger vasodilator response in segments from cirrhotic rats. Pinacidil induced greater K(ATP) currents in cirrhotic myocytes. Expression of RAMP1, calcitonin receptor-like receptor, Kir 6.1 and SUR2B was not modified by liver cirrhosis. Liver cirrhosis increased CGRP release, but did not modify cGMP formation. The decreased vasoconstrictor response to EFS in cirrhosis is mediated by increased vasodilator response to CGRP, as well as increased K(ATP) channel gating. This effect of CGRP may play a role in the splanchnic vasodilatation present in liver cirrhosis.

Receptor activity modifying proteins and their potential as drug targets

The receptor activity modifying proteins (RAMPs) are a family of membrane proteins that interact with some G protein-coupled receptors (GPCRs) to regulate their function. RAMPs can alter GPCR pharmacology and can regulate their signaling as well as trafficking to and from the cell surface. GPCRs have been successfully exploited as drug targets for many years. RAMPs therefore provide a new avenue for drug development, offering opportunities for regulating the function of therapeutically relevant RAMP-interacting GPCRs. RAMPs could be directly targeted themselves or advantage could be taken of the unique RAMP/GPCR interfaces for generating more selective drugs.

Aldosterone and the vascular system

Aldosterone can act in different tissues exerting physiological and pathological effects. At the vascular level, aldosterone affects endothelial function since administration of aldosterone impaired endothelium-dependent relaxations. In addition, the administration of mineralocorticoid receptor antagonists ameliorate relaxation to acetylcholine in models of both hypertension and atherosclerosis and in patients with heart failure. A reduction in nitric oxide levels seems to be the main mechanism underlying this effect due to a reduction in its production as well as an increase in its degradation by reactive oxygen species. Aldosterone is a pro-inflammatory factor that can participate in the vascular inflammatory process associated with different pathologies including hypertension through activation of the NFkappaB system, which mediates the vascular production of different cytokines. This mineralocorticoid also participates in the vascular remodeling observed in hypertensive rats since the administration of eplerenone improved the media-to-lumen ratio in these animals. This effect seems to be due to an increase in extracellular matrix. In summary, aldosterone through mineralocorticoid receptors can participate in the vascular damage associated with different pathologies including hypertension through its prooxidant, pro-inflammatory and profibrotic effects that triggered endothelial dysfunction, an inflammatory process and vascular remodeling.

Increased expression in calcitonin-like receptor induced by aldosterone in cerebral arteries from spontaneously hypertensive rats does not correlate with functional role of CGRP receptor

OBJECTIVE

To analyze the effect of aldosterone on the expression of calcitonin gene-related peptide (CGRP) receptor components, calcitonin-like receptor (CL receptor) and receptor activity modifying protein 1 (RAMP1), as well as the effect of this mineralocorticoid on CGRP-mediated vasodilation in middle cerebral arteries from Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR).

RESULTS

CGRP 0.1 nM-0.1 microM induced a concentration-dependent relaxation that was nitric oxide independent and higher in SHR middle cerebral arteries. CL receptor and RAMP1 expression were similar in both strains. The relaxation to CGRP was not modified by aldosterone 1 microM in either strain, although aldosterone 1 microM increased expression of CL receptor without modifying RAMP1 in segments from SHR rats.

CONCLUSIONS

CGRP elicits greater vasodilation in middle cerebral arteries from SHR than WKY rats, that is nitric oxide independent, and by mechanism independent of CGRP receptor components expression. Although aldosterone increases the expression of CL receptor in SHR, it does not alter vasodilation to CGRP, since RAMP1 expression is not increased. These results indicate that the increase in CL receptor, without an increase in RAMP1, does not correlate with changes in functional role of the CGRP receptor.

Dexamethasone decreases contraction to electrical field stimulation in mesenteric arteries from spontaneously hypertensive rats through decreases in thromboxane A2 release

Glucocorticoids play a role in the control of vascular smooth muscle tone through the alteration of vasoconstrictor and vasodilator factor production. We studied the effect of dexamethasone on vasoconstriction induced by electrical field stimulation (EFS) in rat mesenteric arteries (MAs) and the role of hypertension in this effect. Endothelium-denuded MAs were obtained from Wistar-Kyoto rats and spontaneously hypertensive rats (SHRs). EFS response was analyzed by isometric tension recordings and cyclooxygenase (COX-1 and COX-2) expression by Western blot. Noradrenaline (NA) release was evaluated in segments incubated with [(3)H]NA. Dexamethasone (0.1 and 1 microM; 2-8 h) reduced vasoconstriction to EFS (200 mA, 0.3 ms, 1-16 Hz), in a dose- and time-dependent manner only in SHRs. However, the EFS-induced release of [(3)H]NA was increased in SHR arteries preincubated with dexamethasone (1 microM; 6 h). The thromboxane A(2) (TxA(2)) synthase inhibitor furegrelate (10 microM), the selective COX-2 inhibitor NS-398 (N-[2-cyclohexyloxy-4-nitrophenyl] methanesulfonamide; 10 microM), or the TxA(2) receptor antagonist SQ 29548 (1 microM), reduced EFS and NA induced vasoconstrictor responses. However, the effect of these drugs was abolished in arteries preincubated with dexamethasone. Both dexamethasone and phentolamine (1 microM) inhibited the increased thromboxane B(2) levels observed after EFS. COX-2 protein expression was reduced by dexamethasone in SHR arteries. Results suggest that dexamethasone reduces vasoconstriction to EFS in MAs from SHRs by decreasing COX-2 expression, thereby decreasing the smooth muscle TXA(2) release induced by alpha-adrenoceptor activation. The undetectable COX-2 expression in MAs from normotensive animals explains the noneffect of dexamethasone in their arteries.

RAMPs: the past, present and future

The discovery of receptor-activity-modifying proteins (RAMPs) as accessory proteins required for the appropriate localization and function of certain G-protein coupled receptors (GPCRs) produced a paradigm shift in our understanding of GPCR regulation. Three RAMPs have now been demonstrated to be crucial for various aspects of the life cycle of calcitonin-like receptor (CLR) including endoplasmic reticulum-to-Golgi translocation, internalization and recycling. Although the RAMP-CLR interaction was the first to be identified, other GPCRs belonging to both the class B and C families of GPCRs also seem to be regulated by RAMPs. The recent advances in our knowledge of the cellular and biochemical regulation of RAMPs and how they in turn regulate the life cycle of GPCRs could lead to therapeutic advances in several diseases.

Pathophysiology and therapeutic possibilities of calcitonin gene-related peptide in hypertension

Calcitonin gene related peptide (CGRP), a 37 amino acid neuropeptide, is the most potent vasodilator known. Participation of CGRP in hypertension and related diseases, such as preeclampsia or vasospasm after subarachnoid haemorrage, is one of the most studied topics. In this review we summarize the published roles of CGRP in pathophysiology of hypertension in humans and in experimental models. We also discuss the effects of direct administration of CGRP in the treatment of hypertension and of anti-hypertensive drugs that enhance the release or response of endogenous calcitonin gene-related peptide: angiotensin converting enzyme inhibitors, selective antagonists for the angiotensin II receptor, beta-blockers, magnesium sulphate for preeclampsia and rutaecarpine, as well as the possibilities using CGRP in gene therapy for prevention of vasospasm after subarachnoid haemorrage.