Decrease in the synthesis and release of calcitonin gene-related peptide in dorsal root ganglia of spontaneously hypertensive rat: Role of nitric oxide synthase inhibitors

Antihypertensive properties of a traditional Chinese medicine GAO-ZI-YAO in elderly spontaneous hypertensive rats

AIM

The present study aims to investigate the antihypertensive effect and the underlying mechanism of GAO-ZI-YAO, one of the traditional Chinese medicines, in elderly spontaneous hypertensive rats (SHR).

METHODS

12-month-old male SHRs were randomly divided into five groups on the basis of treatment with different doses of GAO-ZI-YAO or angiotensin II receptor-1 blocker (ARB, Irbesartan) for four weeks. Systolic blood pressure (SBP), and serum levels of nitric oxide (NO), endothelin-1 (ET-1), angiotensin II (Ang II), vascular endothelial growth factor (VEGF), interleukin (IL)-1β, IL-2, IL-6, and tumor necrotic factor (TNF)-α were measured. The pathological changes of ventricular muscle and thoracic aorta were observed by hematoxylin-eosin staining (H&E).

RESULTS

GAO-ZI-YAO treatment reduced SBP in a dose-dependent manner accompanied by the inhibition of the development of cardiovascular remodeling. Although GAO-ZI-YAO treatment markedly increased serum levels of NO and suppressed serum levels of Ang II, this medicine did not affect the serum levels of ET-1 and VEGF. In addition, GAO-ZI-YAO also inhibited inflammatory response parameters (inflammatory cell infiltration in cardiac tissues and serum levels of IL-1β, IL-2, IL-6, and TNF-α) in a dose-dependent manner.

CONCLUSION

GAO-ZI-YAO exerts antihypertensive and anti-cardiovascular-remodeling effects in elderly SHR, which may be through regulation of NO, Ang II production, and inflammation.

Asymmetric dimethylarginine aggravates blood-retinal barrier breakdown of diabetic retinopathy via inhibition of intercellular communication in retinal pericytes

Blood-retinal barrier breakdown is the main pathological characteristics of diabetic retinopathy (DR). Asymmetric dimethylarginine (ADMA) was reported to be elevated in DR patients. In this study, we observed the dynamic profile of ADMA, retinal morphology and permeability of BRB at 2, 4 or 8 week of diabetic rats induced by a single intraperitoneal injection of streptozocin (60 mg/kg) and in cultured rat retinal pericytes pretreated with D-glucose (30 mM) for 1, 3, 5 and 7 days or ADMA (3, 10, 30 μM) for 24, 48 and 72 h, trying to explore the effects of ADMA on blood-retinal barrier in DR. Gap junction intercellular communication (GJIC) and the expression of blood-retinal barrier-specific component connexin 43 (Cx43) were examined in diabetic rats or cultured retinal pericytes to elucidate whether ADMA impacted blood-retinal barrier function via damaging Cx43-GJIC. The results showed that with increasing duration of diabetes, the ultrastructure of blood-retinal barrier of diabetic rats appeared cell junction damage, apoptosis of retinal pericytes and breakdown of barrier successively. The increases in retinal permeability, ADMA levels and Cx43 expression, and abnormal GJIC were observed in diabetic rats and retinal pericytes exposed to D-glucose (30 mM). A glucose-like effect was seen using ADMA or another L-arginine analogue N^G-monomethyl-L-arginine or dimethylarginine dimethylaminohydrolases (DDAHs) siRNA, implicating that ADMA aggravated the breakdown of blood-retinal barrier via damaging Cx43-GJIC.

Effect of Transcutaneous Electrical Stimulation of Nerves on Blood Pressure and Blood Content of Neuropeptide CGRP and Nitric Oxide in Hypertensive Rats with Metabolic Disturbances

The development of arterial hypertension in male Wistar rats with fructose-induced metabolic syndrome (12.5% of fructose solution as the only drinking source for 10 weeks) along with impaired glucose tolerance and increased serum concentration of triglycerides and LPO products caused a decrease in the content of serum blood calcitonin gene-related peptide (CGRP). Low-frequency transcutaneous electrical nerve stimulation (1 mA, 2 Hz, 10 min daily for 2 weeks) performed in 8 weeks after the beginning of fructose treatment reduced systolic BP and serum concentration of triglycerides and LPO produces and improved glucose tolerance. After stimulation, CGRP content in rats maintained on fructose diet returned to normal values and the content of nitric oxide metabolites increased. We hypothesize that CGRP and nitric oxide are involved in mechanisms mediating the therapeutic effect of low-frequency transcutaneous electrical nerve stimulation on arterial hypertension developing in metabolic syndrome.

Exogenous asymmetric dimethylarginine (ADMA) in pathogenesis of ischemia-reperfusion-induced gastric lesions: interaction with protective nitric oxide (NO) and calcitonin gene-related peptide (CGRP)

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) synthesis inhibitor and pro-inflammatory factor. We investigated the role of ADMA in rat gastric mucosa compromised through 30 min of gastric ischemia (I) and 3 h of reperfusion (R). These I/R animals were pretreated with ADMA with or without the combination of l-arginine, calcitonin gene-related peptide (CGRP) or a small dose of capsaicin, all of which are known to afford protection against gastric lesions, or with a farnesoid X receptor (FXR) agonist, GW 4064, to increase the metabolism of ADMA. In the second series, ADMA was administered to capsaicin-denervated rats. The area of gastric damage was measured with planimetry, gastric blood flow (GBF) was determined by H₂-gas clearance, and plasma ADMA and CGRP levels were determined using ELISA and RIA. ADMA significantly increased I/R-induced gastric injury while significantly decreasing GBF, the luminal NO content, and the plasma level of CGRP. This effect of ADMA was significantly attenuated by pretreatment with CGRP, l-arginine, capsaicin, or a PGE₂ analogue. In GW4064 pretreated animals, the I/R injury was significantly reduced and this effect was abolished by co-treatment with ADMA. I/R damage potentiated by ADMA was exacerbated in capsaicin-denervated animals with a further reduction of CGRP. Plasma levels of IL-10 were significantly decreased while malonylodialdehyde (MDA) and plasma TNF-α contents were significantly increased by ADMA. In conclusion, ADMA aggravates I/R-induced gastric lesions due to a decrease of GBF, which is mediated by a fall in NO and CGRP release, and the enhancement of lipid peroxidation and its pro-inflammatory properties.

Angiotensinergic innervation of the kidney: present knowledge and its significance

Intrarenal neurotransmission implies the co-release of neuropeptides at the neuro-effector junction with direct influence on parameters of kidney function. The presence of an angiotensin (Ang) II-containing phenotype in catecholaminergic postganglionic and sensory fibers of the kidney, based on immunocytological investigations, has only recently been reported. These angiotensinergic fibers display a distinct morphology and intrarenal distribution, suggesting anatomical and functional subspecialization linked to neuronal Ang II-expression. This review discusses the present knowledge concerning these fibers, and their significance for renal physiology and the pathogenesis of hypertension in light of established mechanisms. The data suggest a new role of Ang II as a co-transmitter stimulating renal target cells or modulating nerve traffic from or to the kidney. Neuronal Ang II is likely to be an independent source of intrarenal Ang II. Further physiological experimentation will have to explore the role of the angiotensinergic renal innervation and integrate it into existing concepts.

Increased plasma level of asymmetric dimethylarginine in hypertensive rats facilitates platelet aggregation: role of plasma tissue factor

This study was designed to explore the role of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis, in platelet aggregation in hypertension and its possible mechanisms. Spontaneously hypertensive rats (SHR) and L-NAME-induced hypertensive rats were orally administered with L-arginine (1 g/(kg·day) for 14 days. Systolic blood pressure, platelet aggregation, and plasma tissue factor (TF) level and activity were measured. The plasma concentration of ADMA in SHR was determined. In vitro, platelet-rich plasma isolated from Wistar rats was prepared in order to observe the effect of exogenous ADMA on platelet aggregation and TF level and (or) activity in platelet-rich plasma. In both types of hypertensive rats, systolic blood pressure, platelet aggregation, and the level and activity of plasma TF were elevated compared with corresponding control animals. Plasma ADMA level was also increased in SHR. Treatment with L-arginine, a competitor of ADMA, lowered blood pressure and inhibited platelet aggregation concomitantly with a decrease in plasma TF level and activity in both types of hypertensive rats. We also found that exogenous ADMA promoted platelet aggregation and increased TF level and (or) activity in platelet-rich plasma, an effect that was inhibited by pretreatment with L-arginine. Importantly, the enhanced platelet aggregation induced by exogenous ADMA was reduced by pretreatment with anti-TF antibody. The results suggest that endogenous ADMA may be involved in platelet hyperaggregation status in hypertension, and the facilitation of platelet aggregation by ADMA is related to upregulation of the level and activity of plasma TF.

Calcitonin gene-related peptide inhibits angiotensin II-induced endothelial progenitor cells senescence through up-regulation of klotho expression

BACKGROUND

It has been shown that angiotensin II (Ang II) is able to accelerate endothelial progenitor cells (EPCs) senescence through induction of oxidative stress. Calcitonin gene-related peptide (CGRP), a major neurotransmitter of the capsaicin-sensitive sensory nerves, protects endothelial function. Whether CGRP protects against EPCs senescence is unknown.

METHODS AND RESULTS

In cord-derived EPCs, the effects of CGRP on Ang II-induced cell senescence were evaluated by exogenous application of CGRP and rutaecarpine (to stimulate the endogenous CGRP production) or by over-expression of CGRP. The anti-senescence mechanisms of CGRP on EPCs were investigated either by applying CGRP antagonist or by silence of klotho, an anti-aging protein. The results showed that both CGRP and klotho mRNA expression were reduced in Ang II-induced senescent EPCs. Exogenous application of CGRP inhibited Ang II-induced EPCs senescence by down-regulating the expression of NADPH oxidase and reactive oxygen species production. Similarly, rutaecarpine or CGRP I over-expression also inhibited Ang II-induced EPCs senescence. The effects of CGRP and rutaecarpine were reversed by CGRP(8-37), a select antagonist of CGRP receptor and capsazepine, a selective antagonist of transient receptor potential vanilloid 1, respectively. Furthermore, gene silence of klotho markedly attenuated the anti-senescence effect of CGRP on EPCs.

CONCLUSIONS

The results suggest that CGRP can counteract Ang II-induced EPCs senescence through down-regulating the expression of NADPH oxidase and reactive oxygen species production and increasing the production of klotho.

Dimethylarginine metabolism during acute and chronic rejection of rat renal allografts

Background. Dimethylarginines are inhibitors of NO synthesis and are involved in the pathogenesis of vascular diseases. In this study, we ask the question if asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels change during fatal and reversible acute rejection, and contribute to the pathogenesis of chronic vasculopathy.

Methods. The Dark Agouti to Lewis rat strain combination was used to investigate fatal acute rejection. Fischer 344 kidneys were transplanted to Lewis rats to study reversible acute rejection episode and the process of chronic rejection. Isograft recipients and untreated Lewis rats were used as controls. l-arginine derivatives were determined by HPLC, and ADMA-metabolizing enzymes were studied by quantitative RT–PCR and western blotting.

Results. Renal transplantation transiently increased dimethylarginine levels independent of acute rejection. ADMA plasma levels did not importantly differ between recipients undergoing fatal or reversible acute rejection, whereas SDMA was even lower in recipients of Fisher 344 grafts. In comparison to isograft recipients, ADMA and SDMA levels were slightly elevated during reversible, but not during the process of chronic rejection. Increased dimethylarginine levels, however, did not block NO synthesis. Interestingly, protein methylation, but not ADMA degradation, was increased in allografts.

Conclusions. Our data do not support the concept that renal allografts are protected from fatal rejection by dimethylarginines. Dimethylarginines may play a role in triggering chronic rejection, but a contribution to vascular remodelling itself is improbable. In contrast, differential arginine methylation of yet unknown proteins by PRMT1 may be involved in the pathogenesis of acute and chronic rejection.

Involvement of TRPV4-NO-cGMP-PKG pathways in the development of thermal hyperalgesia following chronic compression of the dorsal root ganglion in rats

The aim of the present study was to test the hypothesis that the TRPV4-NO-cGMP-PKG cascade is involved in the maintenance of thermal hyperalgesia following chronic compression of the dorsal root ganglion (DRG) (the procedure hereafter termed CCD) in rats. CCD rats showed thermal hyperalgesia and increased nitrite production. Intrathecal administration of ruthenium red (TRPV4 antagonist, 0.1-1 nmol), TRPV4 antisense ODN (TRPV4 AS, 40 microg, daily for 7 days), N(G)-L-nitro-arginine methyl ester (l-NAME, inhibitor of NO synthase, 30-300 nmol), 1H-[1,2,4]-oxadiazolo [4,3-a] quinoxalin-1-one (ODQ, a soluble guanylate cyclase inhibitor, 50-100 nmol) or 8-(4-Chlorophenylthio) guanosine 3',5'-cyclic Monophosphothioate, Rp-Isomer sodium salt (Rp-8-pCPT-cGMPS, a PKG inhibitor, 25-50 nmol) induced a significant (P<0.001) and dose-dependent increase in the paw withdrawal latency (PWL) compared with control rats, respectively. Ruthenium red (1 nmol), TRPV4 AS (40 microg, daily for 7 days) or L-NAME (300 nmol) decreased nitrite (an index of nitric oxide formation) in the DRG of CCD rats. In addition, the phorbol ester 4alpha-phorbol 12,13-didecanoate (4alpha-PDD, TRPV4 synthetic activator, 1 nmol), co-administered with L-NAME (300 nmol), attenuated the suppressive effect of L-NAME on CCD-induced thermal hyperalgesia and nitrite production. Our data suggested that the TRPV4-NO-cGMP-PKG pathway could be involved in CCD-induced thermal hyperalgesia.