Endogenous nitric oxide reduces microvascular permeability and tissue oedema during exercise in cat skeletal muscle

New perspectives of nitric oxide donors in cardiac arrest and cardiopulmonary resuscitation treatment

Nitric oxide (NO) is often used to treat heart failure accompanied with pulmonary edema. According to present knowledge, however, NO donors are contraindicated when systolic blood pressure is less than 90 mmHg. Based on recent findings and our own clinical experience, we formulated a hypothesis about the new breakthrough complex lifesaving effects of NO donors in patients with cardiac arrest and cardiopulmonary resuscitation therapy. It includes a direct hemodynamic effect of NO donors mediated through vasodilation of coronary arteries in cooperation with improvement of cardiac function and cardiac output through reversible inhibition of mitochondrial complex I and mitochondrial NO synthase, followed by reduction in reactive oxygen species and correction of myocardial stunning. Simultaneously, an increase in vascular sensitivity to sympathetic stimulation could lead to an increase in diastolic blood pressure. Confirmation of this hypothesis in clinical practice would mean a milestone in the treatment for cardiac arrest and cardiopulmonary resuscitation.

Unaltered size selectivity of the glomerular filtration barrier in caveolin-1 knockout mice

The transfer of albumin from blood to tissue has been found to be increased in caveolin-1 knockout (KO) mice. This has been considered to reflect increased microvascular permeability, conceivably caused by an increased endothelial production of nitric oxide (NO) in these mice. To investigate whether such an increase in NO production would also affect glomerular barrier characteristics, the glomerular sieving coefficients (θ) to neutral FITC-Ficoll 70/400 (molecular radius 13–90 Å) were determined in caveolin-1 KO mice vs. their wild-type counterparts. The θ for Ficoll were assessed using high-performance size-exclusion chromatography on blood and urine samples. Furthermore, the transcapillary escape rate (TER) of 125I-labeled albumin and plasma volume (PV) were determined in both types of mice. The kidney expressed low levels of caveolin-1 compared with the lung and bladder, but immunofluorescence associated with vascular structures was evident. Staining was lost in the caveolin-1 KO kidney, as was caveolin-1 expression in the lung and bladder. Despite an increase in the glomerular filtration rate in caveolin-1 KO mice (0.23 ± 0.04 vs. 0.10 ± 0.02 ml/min; both n = 7; P < 0.05), the glomerular Ficoll sieving curves were nearly identical. Furthermore, caveolin-1 KO mice showed an increased PV (6.59 ± 0.42 vs. 5.18 ± 0.13 ml/100 g; P < 0.01) but only a tendency toward an increased TER (14.69 ± 1.59 vs. 11.62 ± 1.62%/h; not significant). It is concluded that in caveolin-1 KO mice the glomerular permeability was not increased, despite the presence of glomerular hyperfiltration. The present data are in line with the concept that the increased transvascular albumin leakage previously found in mice lacking caveolin-1 may be due to an elevation in systemic microvascular pressure due to precapillary vasodilatation, rather than being a consequence of increased microvascular permeability per se.

The effects of disodium pamidronate on human polymorphonuclear leukocytes and platelets: an in vitro study

Recent reports have indicated that, as well as having antiresorptive effects, bisphosphonates could have an application as anti-inflammatory drugs. Our aim was to investigate whether this anti-inflammatory action could be mediated by the nitric oxide (NO) released by the leukocytes migrating to the site of inflammation. In particular, we investigated in vitro the intracellular calcium concentration ([Ca2+](i)), the level of NO released by PMN and platelets, and the PMN myeloperoxidase activity after incubation with disodium pamidronate, since there was a postulated modulatory effect of this aminosubstituted bisphosphonate on leukocytes both in vitro and in vivo. Our data shows that the pamidronate treatment provoked a significant increase in the [Ca2+](i) parallel to the enhancement in NO release, suggesting a possible activation of constitutive nitric oxide synthase, while the myeloperoxidase activity was significantly reduced. In conclusion, we hypothesized that treatment with pamidronate could stimulate NO-production by cells present near the bone compartment, thus constituting a protective mechanism against bone resorption occurring during inflammation. In addition, PMN- and platelet-derived NO could act as a negative feed-back signal to restrict the inflammatory processes.

Sarcolemma-localized nNOS is required to maintain activity after mild exercise

Many neuromuscular conditions are characterized by an exaggerated exercise-induced fatigue response that is disproportionate to activity level. This fatigue does not necessarily correlate with elevated central or peripheral fatigue in patients1, and some patients experience severe fatigue without any demonstrable somatic disease2. Except in myopathies that are due to specific metabolic defects, the mechanism underlying this type of fatigue remains unknown2. With no treatment available, this form of inactivity is a major determinant of disability3. Here we show, using mouse models, that this exaggerated fatigue response is distinct from a loss in specific force production by muscle, and that sarcolemma-localized nNOS signaling in skeletal muscle is required to maintain activity after mild exercise. Of significance, we show that nNOS-null mice do not have muscle pathology and have no loss of muscle specific-force after exercise, but do display this exaggerated fatigue response to mild exercise. In mouse models of nNOS mislocalization from the sarcolemma, prolonged inactivity was only relieved by pharmacologically enhancing the cGMP signal that results from muscle nNOS activation during the nitric oxide signaling response to mild exercise. Our findings suggest that the mechanism underlying the exaggerated fatigue response to mild exercise is a lack of contraction-induced signaling from sarcolemma-localized nNOS, which reduces cGMP-mediated vasomodulation in the vessels that supply active muscle after mild exercise. Notably, sarcolemmal nNOS was reduced in patient biopsies from a large number of distinct myopathies, suggesting a common mechanism of fatigue. Our results suggest that patients with an exaggerated fatigue response to mild exercise would show clinical improvement in response to treatment strategies aimed at improving exercise-induced signaling.

Transvascular protein transport in mice lacking endothelial caveolae

Caveolae are Ω-shaped vesicular structures postulated to play a role in transvascular protein transport. Studies on mice lacking endothelial caveolae, caveolin-1 knockout (Cav-1-KO) mice, indicate increased macromolecular transport rates. This was postulated to be due to the appearance of an alternative pathway. The present study tested whether an alternative pathway had appeared in Cav-1-KO mice. Male Cav-1-KO ( n = 12) and male control mice ( n = 13) were intubated and anesthetized using 2% isoflurane.125I-labeled albumin,131I-labeled immunoglobulin M (IgM), and polydisperse FITC-Ficoll were administered intravenously. During tracer administration, a 90-min peritoneal dialysis dwell was performed. Clearance of tracers to dialysate and permeability-surface area product for glucose were assessed. Transvascular protein transport was higher in Cav-1-KO compared with control mice. Albumin clearance from plasma to peritoneum was 0.088 ± 0.008 μl/min in control and 0.179 ± 0.012 μl/min in Cav-1-KO ( P = 0.001) mice. IgM clearance was 0.049 ± 0.003 and 0.083 ± 0.010 μl/min in control and Cav-1-KO mice, respectively ( P = 0.016). Ficoll clearance was increased in Cav-1-KO mice. In conclusion, the lack of caveolae in Cav-1-KO mice resulted in a marked increase in macromolecular transport. A two-pore analysis of the Ficoll clearance data revealed that the higher transport rate in Cav-1-KO mice was not compatible with the appearance of an alternative pathway for macromolecular transport. In contrast, the higher transperitoneal protein and Ficoll clearance is consistent with passive porous transport through an unperturbed two-pore system, presumably at an elevated capillary hydraulic pressure. Alternatively, the data may be explained by reductions in the selectivity of the endothelial glycocalyx, leading to an increased capillary hydraulic conductivity and large solute filtration.

Nitric oxide as a regulator of inflammatory processes

Nitric oxide (NO) plays an important role in mediating many aspects of inflammatory responses. NO is an effector molecule of cellular injury, and can act as an anti-oxidant. It can modulate the release of various inflammatory mediators from a wide range of cells participating in inflammatory responses (e.g., leukocytes, macrophages, mast cells, endothelial cells, and platelets). It can modulate blood flow, adhesion of leukocytes to the vascular endothelium and the activity of numerous enzymes, all of which can have an impact on inflammatory responses. In recent years, NO-releasing drugs have been developed, usually as derivatives of other drugs, which exhibit very powerful anti-inflammatory effects.