Role of the spinal cord NO/cGMP pathway in the control of arterial pressure and heart rate

The NO-cGMP-PKG Axis in HFpEF: From Pathological Mechanisms to Potential Therapies

Heart failure with preserved ejection fraction (HFpEF) accounts for almost half of all heart failure (HF) cases worldwide. Unfortunately, its incidence is expected to continue to rise, and effective therapy to improve clinical outcomes is lacking. Numerous efforts currently directed towards the pathophysiology of human HFpEF are uncovering signal transduction pathways and novel therapeutic targets. The nitric oxide-cyclic guanosine phosphate-protein kinase G (NO-cGMP-PKG) axis has been described as an important regulator of cardiac function. Suppression of the NO-cGMP-PKG signalling pathway is involved in the progression of HFpEF. Therefore, the NO-cGMP-PKG signalling pathway is a potential therapeutic target for HFpEF. In this review, we aim to explore the mechanism of NO-cGMP-PKG in the progression of HFpEF and to summarize potential therapeutic drugs that target this signalling pathway.

KMUP-1 regulates the vascular calcification in chronic renal failure by mediating NO/cGMP/PKG signaling pathway

OBJECTIVE

To explore the potential mechanism of KMUP-1 in the vascular calcification of chronic renal failure (CRF) through mediating NO/cGMP/PKG pathway, and provide novel insights into the CRF treatment.

METHODS

CRF rats were treated by KMUP-1 with/without L-NNA (a NOS inhibitor) and then performed by ELISA, alizarin red staining, Von Kossa staining, Masson's trichrome, Sirius red staining and CD3 immunohistochemical staining. Simultaneously, vascular smooth muscle cells (VSMCs) were collected from rats to confirm the effect of KMUP-1 on vascular calcification in vitro via NO/cGMP/PKG pathway. Besides, protein and mRNA expressions were determined via Western blotting and qRT-PCR, respectively.

RESULTS

CRF rats were elevated in 24-h urine protein, blood urea nitrogen (BUN), serum creatinine, Cys-C levels and inflammatory cytokines. Besides, CRF rats also showed increased calcium content and ALP level with up-regulated mRNA of osteogenic differentiation-related markers. Furthermore, the up-regulated expressions of eNOS and PKG, as well as down-regulated levels of NOx and cGMP were also found in CRF rats. However, renal failure and vascular calcification of CRF were improved significantly by KMUP-1 treatment via activation of NO/cGMP/PKG pathway. Moreover, KMUP-1 treatment attenuated calcified VSMCs, accompanied by the decreases in the calcified nodules, level of calcium and activity of ALP. In addition, either L-NNA treatment for CRF rats or the calcified VSMCs could antagonize the improving effect of KMUP-1.

CONCLUSION

KMUP-1 can improve the renal function and vascular calcification in CRF rats at least in part by activating NO/cGMP/PKG pathway.

Puerarin Reduces Blood Pressure in Spontaneously Hypertensive Rats by Targeting eNOS

Puerarin is an isoflavonoid isolated from the root of Pueraria lobata (Gegen in Chinese) that has been widely used to treat cardiovascular and cerebrovascular diseases in China. Here, we investigated the hypotensive effects and mechanisms of puerarin in spontaneously hypertensive rats. The qPCR array technique was used to determine the expression of hypertension-related genes. Then, the differentially expressed genes were analyzed using the STRING database. The systolic blood pressure and diastolic blood pressure of rats decreased after the administration of puerarin for nine weeks. Puerarin, but not losartan, also slowed the heart rate of rats. NO and cGMP levels were improved by puerarin. Eighteen differentially expressed hypertension-related genes were identified by comparing the model group with the control group and the high-dose puerarin group with the model group. NO and cGMP levels were increased by high-dose puerarin. High-dose puerarin increased the levels of the phosphorylated eNOS protein and decreased AT1 and Cav1 levels. Based on our results, eNOS was a key target in the mechanism by which puerarin reduced blood pressure, and puerarin represents a potential antihypertensive agent.

Nitric Oxide Orchestrates a Power-Law Modulation of Sympathetic Firing Behaviors in Neonatal Rat Spinal Cords

Nitric oxide (NO) is a diffusible gas and has multifarious effects on both pre- and postsynaptic events. As a consequence of complex excitatory and inhibitory integrations, NO effects on neuronal activities are heterogeneous. Using in vitro preparations of neonatal rats that retain the splanchnic sympathetic nerves and the thoracic spinal cord as an experimental model, we report here that either enhancement or attenuation of NO production in the neonatal rat spinal cords could increase, decrease, or not change the spontaneous firing behaviors recorded from splanchnic sympathetic single fibers. To elucidate the mathematical features of NO-mediated heterogeneous responses, the ratios of changes in firing were plotted against their original firing rates. In log-log plots, a linear data distribution demonstrated that NO-mediated heterogeneity in sympathetic firing responses was well described by a power function. Selective antagonists were applied to test if glycinergic, GABAergic, glutamatergic, and cholinergic neurotransmission in the spinal cord are involved in NO-mediated power-law firing modulations (plFM). NO-mediated plFM diminished in the presence of mecamylamine (an open-channel blocker of nicotinic cholinergic receptors), indicating that endogenous nicotinic receptor activities were essential for plFM. Applications of strychnine (a glycine receptor blocker), gabazine (a GABA_A receptor blocker), or kynurenate (a broad-spectrum ionotropic glutamate receptor blocker) also caused plFM. However, strychnine- or kynurenate-induced plFM was diminished by L-NAME (an NO synthase inhibitor) pretreatments, indicating that the involvements of glycine or ionotropic glutamate receptor activities in plFM were secondary to NO signaling. To recapitulate the arithmetic natures of the plFM, the plFM were simulated by firing changes in two components: a step increment and a fractional reduction of their basal firing activities. Ionotropic glutamate receptor activities were found to participate in plFM by both components. In contrast, GABA_A receptor activities are involved in the component of fractional reduction only. These findings suggest that NO orchestrates a repertoire of excitatory and inhibitory neurotransmissions, incurs a shunting effect on postsynaptic membrane properties, and thus, alters sympathetic firing in a manner of plFM. We propose that the plFM mediated by NO forms a basic scheme of differential controls for heterogeneous sympathetic regulation of visceral functions.

Anti-proliferative effect of the extract of Guangzao (Fructus Choerospondiatis) on cultured rat cardiac fibroblasts

OBJECTIVE

To ascertain if total flavonoids of Guangzao (Fructus Choerospondiatis) (TFFC) extracted from Guangzao (Fructus Choerospondiatis) can inhibit angiotensin II-induced proliferation of cardiac fibroblasts (CFs).

METHODS

CFs were cultured by the differential attachment method. A model of cell proliferation was established by stimulation with Ang II. Cardiac fibroblasts growth was determined using a hemocytometer. Cell proliferation was detected by methyl thiazole tetrazolium. Lactate dehydrogenase activity was measured by chemical colorimetric method.

RESULTS

Proliferation of TFFC-treated (25, 50, 100 mg/L) fibroblasts was significantly less than that of cells in the angiotensin II group (P < 0.01), and TFFC inhibited proliferation in a dose-dependent manner. These inhibitory effects were partly blocked by pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) and 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ).

CONCLUSION

TFFC inhibited angiotensin II-induced proliferation of cardiac fibroblasts via a mechanism that probably involves activation of the NO-cyclic guanosine monophosphate signaling pathway.

Remote intrathecal morphine preconditioning confers cardioprotection via spinal cord nitric oxide/cyclic guanosine monophosphate/protein kinase G pathway

BACKGROUND

Remote intrathecal morphine preconditioning (RMPC) induces cardioprotection, but the underlying mechanisms of this effect is unknown. The aim of this study was to investigate the role of spinal cord nitric oxide/cyclic guanosine monophosphate/protein kinase G (NO/cGMP/PKG) signal pathway in the cardioprotection of RMPC in rats.

MATERIALS AND METHODS

Anesthetized, open chest, male Sprague-Dawley rats were assigned to one of eight treatment groups 3 d after intrathecal catheter placement. Before ischemia and reperfusion, RMPC received intrathecal morphine (3 μg/kg) by three cycles of 5-min infusions interspersed with 5-min infusion free periods. Intrathecally administrated a nonspecific nitric oxide synthase (NOS) inhibitor Nω-Nitro-L-arginine methyl ester (30 nmol), a specific guanylate cyclase inhibitor oxadiazolo [4,3-a] quinoxalin-1-one (11 nmol) and PKG inhibitor KT-5823 (20 pmol) 10 min before RMPC was used to evaluate the role of NO/cGMP/PKG of spinal cord. Ischemia and reperfusion injury were then induced by 30 min of left coronary artery occlusion, followed by 120 min of reperfusion. Infarct size, as a percentage of the area at risk, was determined by 2,3,5-triphenyltetrazolium staining. The content of cyclic guanosine monophosphate in the thoracic spinal cord was determined by radioimmunity protocol; the contents of nitric oxide and activity of NOS in the thoracic spinal cord were determined by nitrate reductase reduction and colorimetric methods; the expression of neuronal NOS (nNOS) and PKG in the thoracic spinal cord were determined by immunohistochemical and Western blotting method; the expression of nNOS messenger RNA was determined by reverse transcription-polymerase chain reaction method.

RESULTS

RMPC group markedly reduced the infarct size compared with the control group. However, the cardioprotection of RMPC could be abolished by pretreatment with Nω-Nitro-L-arginine methyl ester, Oxadiazolo [4,3-a] quinoxalin-1-one, and KT-5823. RMPC enhanced nitric oxide , NOS, and cyclic guanosine monophosphate levels in the spinal cord. Meanwhile, RMPC increased PKG and nNOS protein or messenger RNA expression in the spinal cord.

CONCLUSIONS

Spinal cord NO/cGMP/PKG signaling pathway mediates RMPC-induced cardioprotective effect.

Spinal neuronal NOS activation mediates intrathecal fentanyl preconditioning induced remote cardioprotection in rats

Fentanyl has been widely used in anesthesia and analgesia, especially for cardiovascular surgeries. The aim of the study was to evaluate whether remote intrathecal fentanyl preconditioning (RFPC) provides cardioprotection and the role of spinal nitric oxide synthase (NOS) system in this effect. Fentanyl (0.3μg/kg) was administered intrathecally during RFPC by 3 cycles of 5-minute infusions interspersed with 5-minute infusion free periods. A non-specific nitric oxide synthase (NOS) inhibitor NG-nitro l-arginine methyl ester (l-NAME, 30nmol) and a selective nNOS inhibitor 7-nitroindazole (7-NI, 100nmol) were administered intrathecally 10min before RFPC, and were used to evaluate the involvement of the NOS system of the spinal cord. RFPC group markedly reduced the infarct size compared with control. However, the cardioprotection of RFPC could be abolished by pretreatment with l-NAME and 7-NI. RFPC merely increased the expression of nNOS and did not affect iNOS and eNOS expression. l-NAME reversed nNOS expression up-regulation induced by RFPC treatment. The present study demonstrated that RFPC effectively induced cardioprotection through activating the nNOS in the spinal cord.