Retina derived relaxation is mediated by Kir channels and the inhibition of Ca2+ sensitization in isolated bovine retinal arteries

Retinal relaxing factor (RRF) has recently been identified as a novel paracrine regulator of retinal circulation acting differently from well known mediators of the endothelium and the retina. Herein, we aimed to characterize the relaxing mechanism of the retina, i.e. RRF, by evaluating the role of Ca+2-dependent and -independent signaling mechanisms as well as inward rectifier K+ (KO channels. Retinal relaxation was determined by placing a piece of retinal tissue just on top of the precontracted bovine retinal arteries mounted in a wire myograph. The retina produced a complete relaxation response, which display a biphasic character, in depolarized arteries contracted by L-type Ca2+ channel agonist, Bay k 8644. Blockade of L-type Ca2+ channel by nifedipine, inhibition of sarcoplasmic reticulum Ca2+-ATPase by cyclopiazonic acid or removal of extracellular Ca2+ did not influence the prominent relaxation to the retina. Originally, retinal relaxation was found to be unaffected from the inhibition of myosin light chain kinase by ML7, whereas, completely abolished in the presence of myosin light chain phosphatase (MLCP) inhibitor, Calyculin A. Moreover, the inhibition of Rho kinase by its putative inhibitor, Y-27632 displayed comparable relaxant effects to RRF in retinal arteries precontracted either by prostaglandin F25 or K+, and augmented the moderate response to the retina in K+ precontracted arteries. In addition, retinal relaxation was significantly inhibited and lost its biphasic character in the presence of Kir channel blocker, Ba2+. Our results suggested that inhibition of Ca2+ sensitization through the activation of MLCP, possibly via interfering with Rho kinase, and the opening of Kir channels are likely to be involved in the inhibitory influence of RRF on the retinal arteries. (C) 2015 Elsevier Ltd. All rights reserved

Retina evokes biphasic relaxations in retinal artery unrelated to endothelium, K-V, K-ATP, K-Ca channels and methyl palmitate

Retinal relaxing factor (RRF) is suggested to be released from the retina and to contribute in the maintenance of retinal arterial tone. Herein, we aimed to clarify the effects of retinal tissue in isolated bovine retinal arteries in comparison with choroidal tissue and to evaluate the possible role of endothelium and potassium channels. In parallel, the effects of palmitic acid methyl ester (FAME), a putative vasodilator proposed to be released from the retina, was also examined. A piece of bovine retinal or choroidal tissue was placed within a close proximity on top of retinal arteries mounted in a wire myograph and precontracted with noradrenaline, prostaglandin F-2 alpha, endothelin-1, thromboxane A(2) mimetic, U46619 or potassium (K+). To elucidate possible mechanisms in the effects of retinal tissue, retinal arteries were either deendothelized or incubated with inhibitors of endothelial vasodilators, i.e. nitric oxide (NO) and prostaglandins, or K+ channels. Unlike the choroid, retinal tissue produced rapid, biphasic and complete relaxations in isolated bovine retinal arteries precontracted with various spasmogens acting on distinct receptors. Endothelium removal or preincubation of retinal arteries with inhibitors of NO synthase; L-NOARG (10(-4) M), guanylate cyclase; ODQ (10(-5) M) and cyclooxygenase; indomethacin (10(-5) M), did not cause a significant difference in the relaxation profile. Additionally, retinal relaxations remained unchanged in the presence of respective inhibitors of ATP-sensitive (K-ATP) (glibenclamide, 10(-5) M), voltage-dependent (K-V) (4-aminopyridine, 2 x 10(-3) M), and calcium-activated (K-Ca) (tetraethylammonium 10 mM; charybdotoxin, 10(-7) M; and apamin, 5 x 10(-7) M) K+ channels. Thus, our results provide novel evidence regarding the biphasic relaxing profile of RRF in the retinal artery which was unrelated to endothelium and K+ channels (K-ATP, K-V and K-Ca). Interestingly, PAME (10(-14)-10(-5) M) did not provoke a relaxation in bovine retinal artery suggesting no association with RRF. (C) 2011 Elsevier Inc. All rights reserved

Vasorelaxant and blood pressure lowering effects of alchemilla vulgaris: A comparative study of methanol and aqueous extracts

Background: In the last decade, a growing interest particularly in determining the cardiovascular effects of herbal extracts took place among researchers. Objective: Herein, we aimed to investigate the microvascular and blood pressure lowering effects of two differently processed extracts of the same herb, Alchemilla vulgaris (Rosaceaea), which was revealed to contain high levels of vasoactive compounds. Materials and Methods: For the purpose, endothelium intact rat mesenteric arteries were mounted in a myograph system and contracted with prostaglandin F 2α (PGF 2α: 3 × 10−5 M) or potassium chloride (K + : 40 mM). Then, aqueous and methanol extracts were added at 0.01-10 mg/ml concentrations in a cumulative manner. Results: Both extracts produced relaxations in PGF 2α (3 × 10−5 M) precontracted arteries which were insensitive to the inhibitors of endothelium derived vasoactive substances namely, L G -nitro-L-arginine (10−4 M), ODQ (10−5 M) and indomethacin (10−5 M) or removal of endothelium. Opposite vascular effects were observed when extracts were applied in K + precontracted arteries. In addition, oral administration of the methanol extract of Alchemilla vulgaris, but not the aqueous extract, reduced blood pressure significantly in L-NAME hypertensive rats. Conclusion: Our results demonstrated that the methanol extract of Alchemilla vulgaris has more prominent and favourable vascular effects in normal and experimental hypertensive conditions reinforcing its traditional use in cardiovascular disorders, in particular hypertension. These results most likely give rise to further studies to reveal its mechanism of action and clinical value of this herb

The elevation of intraocular pressure is associated with apoptosis and increased immunoreactivity for nitric oxide synthase in rat retina whereas the effectiveness of retina derived relaxing factor is unaffected

Glaucoma is a progressive ocular disease that stands in the upper rank for the cause of blindness in worldwide. In the present study, we aimed to elucidate the possible disturbances occurred in the layers of retina due to an increase in intraocular pressure (IOP) and to verify the effectiveness of retina derived relaxing factor, i.e., RRF in this pathologic condition. The increase in IOP was induced by cauterization of the three of episcleral veins simultaneously in rats. After 8 weeks period, the retinas excised from the vein cauterized eyes were evaluated for the possible histopathological and ultrastructural alterations as well as for the relaxing effects on isolated bovine retinal and rat mesenteric arteries, in comparison with the retinas obtained from contralateral sham-operated eyes. In the retinas of IOP-elevated eyes, profound morphological deteriorations were determined in the ganglion and outer nuclear cell layers which were associated with an increased number of TUNEL positive cells in the ganglion and inner nuclear cell layers. Increased immunohistochemical stainings for three isoforms of nitric oxide synthase (NOS) were defined in almost all layers of the retinas of IOP-elevated eyes, in which eNOS was abundant particularly in the inner plexiform and ganglion cell layers. An irregular basal folding of retinal pigment epithelium (RPE) and an increased inter lamellar space of photoreceptor cell layer furtherly characterized the prominent degeneration of those layers in the retinas of IOP-elevated eyes. On the other hand, the relaxing effects of the retina obtained from IOP-elevated eyes were determined to be unchanged on the retinal and mesenteric arteries precontracted either with prostaglandin F-2 alpha (PGF(2 alpha), 30 mu M) or potassium chloride (K+, 100 mM), when compared with the relaxations of control retina obtained from contralateral sham operated eyes. Overall, these findings suggested that the elevation of lOP induces prominent structural changes in rat retina particularly in the ganglion and inner layers that is associated with marked apoptosis and increased immunoreactivity for NOS, while the functional effectiveness of retina derived relaxing factor, i.e., RRF is unaffected. (C) 2016 Elsevier Ltd. All rights reserved

Prokineticin receptor-1 induces neovascularization and epicardial-derived progenitor cell differentiation

Objective-Identification of novel factors that contribute to myocardial repair and collateral vessel growth hold promise for treatment of heart diseases. We have shown that transient prokineticin receptor-1 (PKR1) gene transfer protects the heart against myocardial infarction in a mouse model. Here, we investigated the role of excessive PKR1 signaling in heart

Endothelium-dependent vasorelaxant effect of Alchemilla vulgaris methanol extract: a comparison with the aqueous extract in rat aorta

We aimed to investigate the vascular effects of methanol extract (ME) and aqueous extract (AE) of Alchemilla vulgaris (Rosaceaea). Increasing concentrations of the ME (0.01-10 mg/mL) produced relaxations in noradrenaline (NA: 10(-6) M) and K+ (40mM) precontracted aortas while contractions were obtained with the AE (0.01-10 mg/mL). Responses to the ME were inhibited in the presence of putative inhibitors of endothelial vasodilators or after removal of the endothelium. Pretreatment of aortic rings with the ME (10 mg/mL, 20 min) reduced the maximal contractions to NA and K+, whereas an enhanced contractility was observed with the AE (10 mg/mL, 20 min). Total flavonoid content was higher in the ME than in the AE. Quercetin was determined particularly high in the ME while gallic acid was high in the AE. Our results indicated that the ME of A. vulgaris displays favourable vascular effects via endothelium-dependent mechanisms