Nitric oxide modulation of endothelium-derived hyperpolarizing factor in agonist-induced depressor responses in anesthetized rats.

Vasodilators, such as prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF), released from the vascular endothelium are important in the maintenance of systemic blood pressure. Some studies have shown that NO affects EDHF-induced vasodilator responses in isolated perfused blood vessel segments. However, the effects of NO on EDHF-mediated dilation, and their contribution to systemic blood pressure, have not been clarified. Therefore, in the present study we investigated the mechanisms underlying acetylcholine- and bradykinin-induced depressor responses, as well as the interaction between NO and EDHF, by measuring systemic blood pressure in anesthetized rats. In the presence of indomethacin and N(G)-nitro-l-arginine (l-NA; an NO synthase inhibitor), apamin plus charybdotoxin significantly inhibited depressor responses to acetylcholine and bradykinin, whereas glibenclamide, iberiotoxin, quinacrine, catalase, and combination of ouabain plus BaCl2 failed to inhibit EDHF-induced depressor responses. 4-Aminopyridine significantly inhibited depressor responses to acetylcholine, but not to bradykinin. In the presence of indomethacin and l-NA, carbenoxolone, a gap junction inhibitor, significantly inhibited depressor responses to agonists. l-NA alone significantly potentiated agonist-induced depressor responses. In contrast, infusion of sodium nitroprusside, an NO donor, or 8-br-cGMP significantly inhibited depressor responses to agonist. The findings of the present study raise the possibility that agonist-induced depressor responses are elicited by propagation of endothelial hyperpolarization via apamin- plus charybdotoxin-sensitive K(+) channels to smooth muscle cells through gap junctions, but not by diffusible substance(s). It is suggested that, in anesthetized rats, the EDHF-induced depressor response is attenuated in the presence of endogenous and exogenous NO via an increment in cGMP.

Effects of propionyl-L-carnitine on ischemia-reperfusion injury in hamster cheek pouch microcirculation.

BACKGROUND AND PURPOSE: Propionyl-l-carnitine (pLc) exerts protective effects in different experimental models of ischemia-reperfusion (I/R). The aim of the present study was to assess the effects of intravenously and topically applied pLc on microvascular permeability increase induced by I/R in the hamster cheek pouch preparation. METHODS: The hamster cheek pouch microcirculation was visualized by fluorescence microscopy. Microvascular permeability, leukocyte adhesion to venular walls, perfused capillary length, and capillary red blood cell velocity (V(RBC)) were evaluated by computer-assisted methods. E-selectin expression was assessed by in vitro analysis. Lipid peroxidation and reactive oxygen species (ROS) formation were determined by thiobarbituric acid-reactive substances (TBARS) and 2'-7'-dichlorofluorescein (DCF), respectively. RESULTS: In control animals, I/R caused a significant increase in permeability and in the leukocyte adhesion in venules. Capillary perfusion and V(RBC) decreased. TBARS levels and DCF fluorescence significantly increased compared with baseline. Intravenously infused pLc dose-dependently prevented leakage and leukocyte adhesion, preserved capillary perfusion, and induced vasodilation at the end of reperfusion, while ROS concentration decreased. Inhibition of nitric oxide synthase prior to pLc caused vasoconstriction and partially blunted the pLc-induced protective effects; inhibition of the endothelium-derived hyperpolarizing factor (EDHF) abolished pLc effects. Topical application of pLc on cheek pouch membrane produced the same effects as observed with intravenous administration. pLc decreased the E-selectin expression. CONCLUSIONS: pLc prevents microvascular changes induced by I/R injury. The reduction of permeability increase could be mainly due to EDHF release induce vasodilatation together with NO. The reduction of E-selectin expression prevents leukocyte adhesion and permeability increase.

Inducing effect of total flavones in rhododendra on endothelium-derived hyperpolarizing factor responses in cerebral basilar artery of rats subjected to global cerebral ischemia reperfusion / 中草药

Objective: To study the effect of endothelium-derived hyperpolarizing factor (EDHF)-mediated responses of relaxation and hyperpolarization of vascular smooth muscle cell (VSMC) of rat cerebral basilar artery (CBA) subjected to cerebral ischemia/reperfusion (I/R) to total flavones in rhododendra (TFR). Methods: The model of global cerebral I/R in rats was made by 4-vessel occlusion (4-VO). The vasodilation and resting membrane potential (RMP) of VSMC of rat CBA were detected in vitro. Results: In the presence of 3×10-5 mol/L Nω-nitro-L-arginine-methyl-ester (L-NAME, an inhibitor of nitric oxide synthase) and 1×10-5 mol/L Indomethacin (Indo, an inhibitor of PGI2 synthesis), the global cerebral I/R markedly enhanced 1×10-7-1×10-5 mol/L acetylcholine (Ach)-elicited relaxation and hyperpolarization of RMP of VSMC in rat CBA. In the presence of L-NAME and Indo, 11-2 700 mg/L TFR induced significant and dose-dependent hyperpolarization of RMP of VSMC and relaxation of rat CBA subjected to global cerebral I/R. The hyperpolarization and relaxation were obviously inhibited by tetraethylammonium (an inhibitor IKCa at 1 mmol/L) and 1×10-4 mol/L dl-propargylglycine (PPG), an inhibitor of endogenous hydrogen sulfide (H2S) synthase. Conclusion: Global cerebral I/R could enhance the non-NO-non-PGI2-mediated responses of hyperpolarization and vasorelaxation in rat CAB. In rat CAB subjected to global cerebral I/R, TFR could significantly induce this non-NO-non-PGI2 hyperpolarization and relaxation, the so-called EDHF response that might be mediated by endogenous H2S.

The endothelium in health and disease: A discussion of the contribution of non-nitric oxide endothelium-derived vasoactive mediators to vascular homeostasis in normal vessels and in type II diabetes.

Endothelial dysfunction is considered as a major risk factor of cardiovascular complications of type I and types II diabetes. Impaired endothelium-dependent vasodilatation can be directly linked to a decreased synthesis of the endothelium-derived nitric oxide (NO) and/or an increase in the production of reactive oxygen species such as superoxide. Administration of tetrahydrobiopterin, an important co-factor for the enzyme nitric oxide synthase (NOS), has been demonstrated to enhance NO production in prehypertensive rats, restore endothelium-dependent vasodilatation in coronary arteries following reperfusion injury, aortae from streptozotocin-induced diabetic rats and in patients with hypercholesterolemia. Tetrahydrobiopterin supplementation has been shown to improve endothelium-dependent relaxation in normal individuals, patients with type II diabetes and in smokers. These findings from different animal models as well as in clinical trials lead to the hypothesis that tetrahydrobiopterin, or a precursor thereof, could be a new and an effective therapeutic approach for the improvement of endothelium function in pathophysiological conditions. In addition to NO, the endothelium also produces a variety of other vasoactive factors and a key question is: Is there also a link to changes in the synthesis/action of these other endothelium-derived factors to the cardiovascular complications associated with diabetes? Endothelium-derived hyperpolarizing factor, or EDHF, is thought to be an extremely important vasodilator substance notably in the resistance vasculature. Unfortunately, the nature and, indeed, the very existence of EDHF remains obscure. Potentially there are multiple EDHFs demonstrating vessel selectivity in their actions. However, until now, identity and properties of EDHF that determine the therapeutic potential of manipulating EDHF remains unknown. Here we briefly review the current status of EDHF and the link between EDHF and endothelial dysfunction associated with diabetes. (Mol Cell Biochem 263: 21-27, 2004).