Myogenic vascular regulation in skeletal muscle in vivo is not dependent of endothelium-derived nitric oxide.

The hypothesis, based on in vitro experiments on large conduit arteries, that endothelium-derived nitric oxide is a mediator of vascular myogenic reactivity was tested in cat gastrocnemius muscle in vivo. This was done by comparing, in the absence and presence of effective endothelium-derived nitric oxide blockade by the specific inhibitors NG-monomethyl-L-arginine or NG-nitro-L-arginine methyl ester, myogenic responses in defined consecutive vascular sections to dynamic vascular transmural pressure stimuli, to arterial occlusion (reactive hyperaemia), and to arterial pressure changes (autoregulation of blood flow and capillary pressure). The results demonstrated that the myogenic vascular reactivity to quick ramp transmural pressure stimuli was not attenuated by endothelium-derived nitric oxide blockade, but rather reinforced. The amplitude of the reactive hyperaemia response was unaffected by endothelium-derived nitric oxide blockade, but its duration was shortened because of faster myogenic constriction, especially of large-bore arterial resistance vessels greater than 25 microns, in the recovery phase. Both the improved myogenic responsiveness to transmural pressure stimuli and the shortening of the reactive hyperaemia by endothelium-derived nitric oxide blockade suggested that endothelium-derived nitric oxide released in vivo acts as a 'metabolic' factor which certainly does not improve, but rather depresses myogenic vascular reactivity. Autoregulation of blood flow and capillary pressure were well preserved in the presence of endothelium-derived nitric oxide blockade. It was concluded from the results of these multifaceted tests that myogenic vascular regulation in skeletal muscle in vivo seems independent of endothelium-derived nitric oxide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endogenous nitric oxide as a physiological regulator of vascular tone in cat skeletal muscle during haemorrhage

The problem whether endogenous nitric oxide (NO) may serve as a true physiological regulator of vascular tone in vivo was approached by testing its role during graded acute haemorrhage with the aid of the nitric oxide synthase (NOS) inhibitor l -NAME. The study was performed on the vascular bed of cat skeletal muscle with a technique permitting quantitative recordings of vascular resistance in the whole vascular bed (R_T) and in its consecutive sections, the proximal arterial resistance (‘feeder’) vessels (>25 μm; R_a,prox), the small arterioles (<25 μm) and the veins. NO blockade by close-arterial l -NAME infusion in the control situation increased R_T from 16.3 to 33.0 PRU (+102%), because of a selective increase in R_a,prox by 16.7 PRU. A 35% blood loss per se raised R_T from 13.6 to 21.7 PRU. Superimposed NO blockade in this state caused a much stronger vasoconstriction than in the control situation, increasing R_T to 60.9 PRU (+181%) and R_a,prox by 40.5 PRU, which indicated an ～2.4-fold increase (P< 0.001) in the NO dilator influence in the R_a,prox section above control. The effect was independent of autonomic nerves. The increased NO dilator influence during haemorrhage most likely was caused by an increased production of endothelium-derived nitric oxide (EDNO). The constrictor response to l -NAME was graded in relation to the blood loss (17.5 vs. 35%). The results indicate that EDNO functions as a physiological regulator of vascular tone in the arterial ‘feeder’ vessels during haemorrhage, serving to counterbalance to a significant extent the concomitant adrenergic constriction, and thereby preventing critical reduction of blood flow and untoward heterogeneous flow distribution within the tissue.     

Role of nitric oxide in skeletal muscle: synthesis,distribution and functional importance

Over the last two decades, nitric oxide (NO) has been established as a novel mediator of biological processes, ranging from vascular control to long-term memory, from tissue inflammation to penile erection. This paper reviews recent research which shows that NO and its derivatives also are synthesized within skeletal muscle and that NO derivatives influence various aspects of muscle function. Individual muscle fibres express one or both of the constitutive NO synthase (NOS) isoforms. Type I (neuronal) NOS is localized to the sarcolemma of fast fibres; type III (endothelial) NOS is associated with mitochondria. Isolated skeletal muscle produces NO at low rates under resting conditions and at higher rates during repetitive contraction. NO appears to mediate cell–cell interactions in muscle, including vasodilation and inhibition of leucocyte adhesion. NO also acts directly on muscle fibres to alter cell function. Muscle metabolism appears to be NO-sensitive at several sites, including glucose uptake, glycolysis, mitochondrial oxygen consumption and creatine kinase activity. NO also modulates muscle contraction, inhibiting force output by altering excitation–contraction coupling. The mechanisms of NO action are likely to include direct effects on redox-sensitive regulatory proteins, interaction with endogenous reactive oxygen species, and activation of second messengers such as cyclic guanosine monophosphate (cGMP). In conclusion, research published over the past few years makes it clear that skeletal muscle produces NO and that endogenous NO modulates muscle function. Much remains to be learned, however, about the physiological importance of NO actions and about their underlying mechanisms.     

Effects of glyceryl trinitrate,nitroprusside and nitric oxide on arterial,venous and capillary functions in cat skeletal muscle in vivo

The aim of the present study was to analyse quantitatively, on a cat gastrocnemius preparation in vivo, the effects of i.a. or i.v. administered glyceryl trinitrate (GTN), sodium nitroprusside (SNP) or nitric oxide (NO dissolved in saline) on vascular resistance (tone) in the following consecutive vascular sections: Large-bore arterial resistance vessels (> 25 μm), small arterioles (< 25 μm), and the veins. Effects on hydrostatic capillary pressure (P_cv) and transcapillary fluid exchange were simultaneously recorded. Close-arterially infused GTN (1–4096μg kg tissue^-1 min^-1), SNP (0.5–32 %mUg kg tissue^-1 min^-1) and NO (0.14-0.82 mg kg tissue^-1 min^-1) elicited a generalized dose-dependent dilator response in all three sections, though with a preferential action on the arterial side. Further, these agents caused an increase in P_cv and transcapillary fluid filtration. The sites of action along the vascular bed of these exogenous vasodilators differed from that previously established for endogenous EDNO. Infusion of GTN, SNP and NO during EDNO blockade (L-NAME) could, therefore, not restore the vascular resistance distribution to that prevailing in the initial control state. Myogenic vascular reactivity to standardized transmural pressure stimuli was clearly depressed by GTN and SNP. Intravenously infused GTN (4–512 μg kg body wt^-1 min^-1) and SNP (4–64μg kg body wt^-1 min^-1) decreased arterial pressure and elicited, via reflex sympathetic activation, a dose-dependent vasoconstriction in skeletal muscle, a decrease in P_cv, and net transcapillary fluid absorption. The constrictor response thus overruled the direct dilator effect of the drugs. The plasma volume expansion known to result from long-term systematic administration of nitrovasodilators seems in part to be caused by transcapillary fluid absorption in skeletal muscle.     

In vivo effects of endothelin-2, endothelin-3 and ETA receptor blockade on arterial,venous and capillary functions in cat skeletal muscle

Ekelund , U. 1994. In vivo effects of endothelin-2, endothelin-3 and ET_A receptor blockade on arterial, venous and capillary functions in cat skeletal muscle. Acta Physiol Scand 150, 47–56. Received 31 March 1993, accepted 25 May 1993. ISSN 0001–6772. Department of Physiology & Biophysics, University of Lund, Sweden. This study describes, in quantitative terms, the effects of endothelin-2 and endothelin-3 on vascular tone (resistance) in large-bore arterial resistance vessels (> 25 /μm), small arterioles (< 25 μm) and the veins, as well as on capillary pressure and fluid exchange in cat gastrocnemius muscle in vivo. Infusion of endothelin-2 or endothelin-3 (200–1600 ng kg^-1 min^-1, i.a.) elicited an initial transient dilation, followed by a dose-dependent, slowly developing constrictor response, being maintained after cessation of the infusion. At the dose of 400 ng kg^-1 min^-1 (n= 9), infused i.a. during 20 min, endothelin-2 caused an average increase in total regional vascular resistance of 80%, and endothelin-3 of 35%, and the site of constrictor action of both peptides was preferentially located to the small arterioles. Endothelin-2 also constricted the veins and, hence, evoked a pronounced capacitance response, whereas endothelin-3 was devoid of any venoconstrictor effect. This difference, via effects on the pre-/post-capillary resistance ratio, led to a more pronounced fall of capillary pressure in response to endothelin-3 than to endothelin-2. The new specific competitive ET_A receptor antagonist, FR 139317, abolished the vasoconstrictor response to both endothelin-2 and endothelin-3 in vivo, whereas the preceding vasodilator responses were unaffected. These results, taken together with those of our previous analogous study of the effects of endothelin-1, indicated that all three endothelins were approximately equally as effective in eliciting the transient dilator response in skeletal muscle in vivo, whereas the order of vasoconstrictor activity was endothelin-1 > endothelin-2 > endothelin-3. Due to an especially pronounced venoconstrictor activity of endothelin-1, this peptide, in contrast to endothelin-2 and -3, evoked a rise in capillary pressure, with a consequent net transcapillary fluid filtration and muscle tissue oedema formation. The results further indicated that the vasoconstrictor responses to all endothelins in skeletal muscle were mediated by the ET_A receptor, whereas the initial transient vasodilator responses seemed to be mediated by the ET_B receptor.     

Endogenous nitric oxide as a probable modulator of pulmonary circulation and hypoxic pressor response in vivo

The objective of this study was to investigate the role of endogenous nitric oxide, formed from L-arginine, in the regulation of pulmonary circulation in vivo, with special reference to the hypoxic pressor response. In artificially ventilated open-chest rabbits, pulmonary vascular resistance at normoxic ventilation (F₁₀₂= 21 %) was 78C 16 cmH₂O ml^-l min 1000^-1 (mRU_L). Hypoxic ventilation (F₁₀₂= 10%) increased pulmonary vascular resistance to 117 ± 17 mRU_L. N^w-nitro-L-arginine methylester (L-NAME), an inhibitor of nitric oxide synthase, increased pulmonary vascular resistance at normoxic ventilation to 192 ± 28 mRU_L and during hypoxic ventilation to 462 ± 80 mRU_L. During N^w-nitro-l-arginine methylester infusion there was also an increase in mean arterial blood pressure as well as a decrease in cardiac output that was even more pronounced during hypoxic ventilation. L-arginine reversed the effect of N^w-nitro-l-arginine methylester on pulmonary vascular resistance at normoxic ventilation to 140 ± 26 mRU_L and at hypoxic ventilation to 239 ± 42 mRU_L. In spontaneously breathing closed-chest rabbits, N^w-nitro-L-arginine methylester evoked a marked decrease in arterial P_o2, and increases in respiration frequency and central venous pressure, while blood pH, P_CO2 and base excess remained unchanged. Taken together these findings indicate that endogenous nitric oxide, formed from L-arginine, might be a regulator of ventilation-perfusion matching at normoxic ventilation, and that nitric oxide acts as an endogenous modulator of the hypoxic pressor response.     

Sympathetic a-adrenergic control of large-bore arterial vessels,arterioles and veins,and of capillary pressure and fluid exchange in whole-organ cat skeletal muscle

The sympathetic nervous control of the vascular bed of cat gastrocnemius muscle was studied with a new whole-organ technique which permits simultaneous, continuous and quantitative measurements of capillary pressure (P_c), capillary fluid exchange and resistance reactions in the whole vascular bed and in its three consecutive sections: large-bore arterial vessels (> 25 μm), arterioles (< 25 μm) and veins. The results demonstrated a distinct neural control of all three consecutive vascular sections, graded in relation to the rate of nerve excitation up to maximum at 16 Hz. Stimulation at high rates, which in the steady state caused an average rise of overall regional resistance from 15.3 to 120 PRU (7.8-fold increase), thus raised large-bore arterial vessel resistance from 8.8 to 64 PRU (7.3-fold increase), arteriolar resistance from 4.5 to 49 PRU (10.9-fold increase) and venous resistance from 2.0 to 7 PRU (3.5-fold increase). The rate of resistance development (PRU s^-1) of the sympathetic constrictor response was much higher in the arteriolar than in the other sections, which indicates that the neural control is especially prompt and efficient in the arterioles. A passive component was shown to contribute to the described responses only on the venous side, but in no case by more than 10% of the total sympathetic venous resistance response, which thus is mainly active. Of special functional importance was that the new technique provided information about the adrenergic control of P_c, in absolute figures. From the control value of 19 mmHg, graded sympathetic stimulation caused a graded decline in P_c, at maximum constriction by about 7 mmHg. This resulted in marked net transcapillary fluid absorption, in turn increasing plasma volume.     

Effects of angiotensin-converting enzyme inhibition on arterial,venous and capillary functions in cat skeletal muscle in vivo

The aim of the present study was to analyse quantitatively, on a cat gastrocnemius muscle preparation in vivo, the effects of local angiotensin-converting enzyme (ACE) inhibition by enalaprilat on total regional vascular resistance (tone) and its distribution to the large-bore arterial resistance vessels (>25 μm), the small arterioles (<25 μm) and the veins. Associated effects on capillary pressure and fluid exchange were also studied. Close-arterial infusion of enalaprilat (0.05–0.20 mg kg muscle tissue min^-1) elicited a moderate dilator response in all three consecutive sections of the muscle vascular bed, an increase in capillary pressure and transcapillary fluid filtration. This dilation could be abolished by the selective bradykinin B₂-receptor antagonist Hoe 140 (2 mg kg^-1 min^-1, i.a.), indicating that the dilator mechanism of ACE inhibition was an increased local concentration of bradykinin, and hardly at all a decreased concentration of angiotensin (AT) II. The generalized dilator response to ACE inhibition along the vascular bed suggested a relatively uniform distribution of ACE from artery to vein and this was further supported by the finding that a close-arterial infusion of AT I (0.04–0.32 μg kg^-1 min^-1), which was vasoactive only after conversion to AT II by local ACE, elicited a generalized constrictor response in all three vascular sections. In contrast, infused AT II (0.01–0.16 μg kg^-1 min^-1) constricted almost selectively the large-bore arterial vessels. The specific angiotensin AT₁-receptor antagonist losartan (2 mg kg^-1 min^-1, i.a.) abolished the constrictor response to AT II but did not affect vascular tone under control conditions, indicating that AT II is not involved in the initiation of basal vascular tone in muscle. These results, taken together, indicate that under basal conditions vascular ACE contributes to the local control of vascular tone in skeletal muscle by degrading the endogenous dilator bradykinin, and not by converting AT I into vasoconstrictor AT II.     

The influence of nitric oxide on in vivo human skeletal muscle properties

We have investigated the action of exogenous nitric oxide (NO) on the strength and contractile properties of human skeletal muscle working in vivo. Maximum isometric voluntary contraction force (MVC) of the quadriceps was measured and superimposed electrical stimulation was used to estimate the level of activation and ‘true maximum force’ (TMF). Force–frequency relationships were determined to assess changes in contractile properties of the muscle. Subjects in the experimental group (E, n=10) were measured before and during two separate periods of treatment with different doses of glyceryl trinitrate, a NO donor, delivering 100 (GTN100) or 200 (GTN200) μg h^–1 as a trans‐dermal patch. A control group (C, n=6) was measured during two similar periods whilst taking an oral placebo. There was a significant increase in strength with GTN200 (MVC: +5.15%; TMF: +3.87%). There was no change in the strength of group C. There was a trend towards reduced forces at submaximal frequencies with GTN administration but the most notable change was a decline in twitch force (approximately 12%, P < 0.05) with GTN100 treatment and this remained depressed throughout the study. No changes were seen in the contractile properties of the control group C. The present results show that GTN treatment increased maximum voluntary strength but decreased twitch tension. The time course and dose–response characteristics indicate that these are two separate actions of NO on human muscle working in vivo.     

The nitric oxide pathway is an important modulator of stress-induced fever in rats

Psychological stress evokes a number of physiological responses, including a rise in body temperature (T(b)), which has been suggested to be the result of an elevation in the thermoregulatory set point, i.e., a fever. This response seems to share similar mechanisms with infectious fever. A growing number of studies have provided evidence that nitric oxide (NO) has a modulatory role in infectious fever, but no report exists about the participation of NO in stress fever. Thus, the present study aimed to verify the hypothesis that NO modulates stress fever by using restraint stress as a model. To this end, we tested the effects of the non-specific NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) or its inactive enantiomer N(G)-nitro-D-arginine methyl ester (D-NAME) on colonic T(b) of restrained or unrestrained rats. A rapid increase in T(b) was observed when animals were submitted to restraint. Intravenous (i.v.) injection of L-NAME at a dose (10 mg/kg) that caused no change in T(b) when administered alone significantly attenuated the elevation in T(b) elicited by stress, indicating that the NO pathway may mediate stress fever. Moreover, intracerebroventricular (i.c.v.) L-NAME (250 microg/microl) caused a rise in T(b) of euthermic animals and enhanced stress fever, supporting that NO in the central nervous system (CNS) leads to a reduction in T(b) and, therefore, this is unlikely to be the site where NO may mediate stress fever. Taken together, these data indicate that the NO pathway plays an important role in modulating restraint stress-induced fever in rats.     

The effect of platelet-activating factor (PAF) on nasal airway resistance in healthy subjects is not mediated by nitric oxide

BACKGROUND: The nose is an important source of nitric oxide (NO) in man, but the relevance of NO production to the response to inflammatory mediators is not clear. METHODS: In this study, we evaluated the effect of NO inhibition on nasal airway resistance (NAR) at baseline, after an acute challenge with platelet-activating factor (PAF), a potent proinflammatory factor, and after an acute challenge with bradykinin (BK), both of which are mediators of allergic rhinitis in man. Eight healthy subjects were enrolled in the study. Nasal NO production was measured by the chemiluminescence method, and NAR was measured by active anterior rhinomanometry. RESULTS: Basal nasal NO concentration was 500.6+/-115.6 ppb; it significantly decreased after topical administration of the NO-synthase inhibitor L-NAME, and the NO-synthase substrate L-arginine caused a recovery in NO production. The administration of L-NAME did not cause any change in basal NAR. In a double-blind fashion, we performed nasal challenge with PAF and BK after topical pretreatment with either placebo or L-NAME. After placebo pretreatment, both PAF and BK caused a significant increase in NAR (respectively, from 0.29+/-0.11 Pa s cm(-3) to 0.75+/-0.21 Pa s cm(-3), and from 0.36+/-0.18 Pa s cm(-3) to 0.71+/-0.25 Pa s cm(-3); P<0.001, n=8). Pretreatment with L-NAME did not prevent the PAF-induced increase in NAR (from 0.31+/-0.10 Pa s cm(-3) to 0.71+/-0.27 Pa s cm(-3)), whereas it prevented the BK-induced increase in NAR (from 0.33+/-0.15 Pa s cm(-3) to 0.43+/-0.16 Pa s cm(-3)). CONCLUSIONS: Topical administration of the NO-synthase inhibitor L-NAME at doses sufficient to decrease NO nasal production does not prevent the PAF-induced increase in NAR, indicating that NO generation in vivo is not involved in the nasal response to PAF.     

Metabolic control of large-bore arterial resistance vessels,arterioles, and veins in cat skeletal muscle during exercise

The metabolic control of the vascular bed in cat gastrocnemius muscle during exercise was studied with a new technique (Björnberg et al. 1988) permitting continuous and simultaneous recordings of arteriolar and capillary pressures, and of resistances in the following consecutive vascular section: proximal arterial resistance vessels > 25 μm, arterioles < 25 μm, and on the venous side. The study thereby provided quantitative data for resistance and active intrinsic tone in these vascular segments at rest, during graded exercise vasodilatation, and in the post-exercise period. Slight activation of the metabolic control system by low-frequency somatomotor nerve stimulation (light exercise') caused inhibition of intrinsic tone and decreased vascular resistance selectively in the arteriolar section. At increasing workloads, arteriolar resistance was further decreased, but resistance and tone in the proximal arterial resistance vessels and the veins then became clearly reduced as well. This difference in effectiveness of the metabolic control system on the different segments of the vascular bed was expressed quantitatively in terms of a ‘metabolic vasodilator index’. Graded activation of the metabolic control system led to a marked segmental redistribution of intrinsic vascular tone, in turn resulting in an increased pressure drop across the proximal arterial vessels and the veins and a decreased pressure drop over the arterioles. The observed decrease in the pre- to post-capillary resistance ratio caused, at a constant arterial pressure of 100 mmHg, a graded increase in capillary pressure with increasing workloads, at maximum vasodilatation by an average value of 14 mmHg above the resting control value of 15.4 ± 0.6 mmHg. In the post-exercise period, recovery of vascular tone to control was more rapid in the proximal arterial resistance vessels and the veins than in the arteriolar segment.     

Effect of hypoxic hypoxia and ritanserin on capillary flow and oxygenation in rabbit skeletal muscle

Gustafsson , U., Sjöberg , F., Lewis , D. H. & Thorborg , P. 1994. Effect of hypoxic hypoxia and ritanserin on capillary flow and oxygenation in rabbit skeletal muscle. Acta Physiol Stand 150, 39–45. Received 2 April 1993, accepted 21 July 1993. ISSN 0001–6772. Clinical Research Centre and the Burns Unit, Department of Hand and Plastic Surgery, and Department of Anaesthesiology, University Hospital, Linkoping, Sweden, and Dept of Anesthesiology, University of Rochester Medical Center, NY, USA. This study examined capillary flow and oxygenation in rabbit skeletal muscle during hypoxic hypoxia (inspired oxygen fraction = 0.10) and after administration of ritanserin (highly selective 5-Hydroxytryptamine-2-receptor antagonist). Capillary flow (hydrogen clearance) or oxygen pressure was measured with a multiwire micro-electrode which was placed on the surface of the left vastus medialis muscle. For measurement of regional microcirculatory blood flow a laser-Doppler flowmeter probe was placed on the contralateral muscle. An experimental sequence with normoxaemia (arterial Po₂ 12.5 kPa), followed by hypoxaemia (arterial Po₂ 3.9 kPa) and thereafter sustained hypoxaemia (arterial Po₂ 4.0 kPa) during which ritanserin (0.035 mg kg^-1 i.v.) was administered, was used. During hypoxaemia a decrease was seen in mean arterial pressure (MAP) by 27%, capillary flow by 25%, muscle oxygen pressure by 32% and laser-Doppler flowmetry (LDF) flow by 24%. After the administration of ritanserin the mean arterial pressure was further reduced by 7%, whereas the capillary flow increased by 59% and the muscle oxygen pressure by 31 %. The LDF flow remained unchanged. These results demonstrate that, in this animal model, a decrease in skeletal muscle capillary flow and oxygenation during hypoxaemia can be reversed by the administration of ritanserin, despite a further reduction in blood pressure.     

Demonstration of endothelium-mediated increase in vascular smooth muscle cGMP,in a flexible coculture model

The purpose of this study was to test the feasibility of applying a novel coculture model for the investigation of endothelium-derived relaxing factor (EDRF) as well as exploring its applicability for investigating important cell-to-cell interactions. Bovine aortic endothelial cells (EC) were grown on micropore filters while porcine aortic smooth muscle cells (SMC) were grown separately on plates. When confluent these two cell layers were cocultured such that the EC maintained proper polarity and orientation to the underlying SMC. We found that coculturing EC with SMC for five minutes caused significant increase in SMC cGMP, 43±4 vs 268±13 fmols/well (p<0.0001). This EC-mediated effect was further augmented with EDRF agonists and with L-arginine supplementation, but was inhibited by nitro-L-arginine methyl ester (NAME) and reduced hemoglobin. When the EC were cocultured with subendothelial THP-1 monocytes for three hours prior to the SMC coculture, the EC mediated increase in SMC cGMP, both stimulated and unstimulated, was significantly reduced. We conclude that this flexible coculture model can be used to study EDRF release from EC and can be applied to study important cell-to-cell interactions that have been difficult to address in other models.     

Attenuation of the exercise‐induced increase in skeletal muscle Flt‐1 mRNA by nitric oxide synthase inhibition

We investigated the vascular endothelial growth factor (VEGF) receptor [fms‐like‐tyrosine kinase (Flt‐1 and fetal liver kinase‐1 (Flk‐1)] response to acute exercise. In female Wistar rats, the VEGF receptor messenger RNA (mRNA) response to a single acute exercise bout was examined using semi‐quantitative Northern blot from the left gastrocnemius muscles at rest and post‐exercise at 0, 1, 2, 4, 8, 16, 24 and 48 h. Exercise altered both Flt‐1 and Flk‐1 mRNA, with significant increases in Flt‐1 mRNA at 1 and 24 h. However, post‐hoc analysis was unable to discern the time point where a significant increase in Flk‐1 mRNA occurred. To investigate the regulation of Flt‐1 mRNA by exercise we examined if nitric oxide synthase (NOS) inhibition alters the Flt‐1 mRNA response. Eight groups [Condition: Rest or Exercise; Drug: Saline, 30 mg kg^–1N^ω‐nitro‐L ‐arginine methyl ester (L ‐NAME), 300 mg kg^–1L ‐NAME or 300 mg kg^–1D ‐NAME] were used to determine the effect of NOS inhibition on the Flt‐1 mRNA response to exercise. L ‐NAME, a known NOS inhibitor, attenuated the exercise‐induced increase in Flt‐1 mRNA by ～50%. These findings suggest that: (1) exercise alters Flt‐1 and Flk‐1 gene expression; and (2) NO is important in the regulation of the Flt‐1 gene response to exercise.     

Glutamate-induced free radical formation in rat brain synaptosomes is not dependent on intrasynaptosomal mitochondria membrane potential

Glutamate induces reactive oxygen species formation (ROS) in neurons. Free radicals can potentially be synthesized by NADPH oxidase or mitochondria. The primary source of ROS origin has yet to be identified. In addition, pro-oxidant action of glutamate receptors on neuronal presynaptic terminals is still not characterized. We investigated the influence of glutamate and agonists of its ionotropic receptors on ROS formation detected by fluorescent dye DCFDA in rat brain synaptosomes. Glutamate in concentration 10 and 100μM led to an increase of probe fluorescence pointing to free radical accumulation. This effect was mimicked by 100μM of NMDA or 100μM of kainate. Glutamate-induced ROS formation was sensitive to NMDA inhibitors MK-801 (10μM), NO synthase (NOS) inhibitor l-NAME (100μM) and NADPH oxidase inhibitors DPI (30μM) and not affected by mitochondrial uncoupler CCCP (10μM) and mitochondrial toxins rotenone (10μM)+oligomycin (5μg/ml). We also showed that 100μM of glutamate leads to a decrease of intrasynaptosomal mitochondrial potential monitored by fluorescent dye Rhodamine-123. Hence, the depolarization of intrasynaptosomal mitochondria is not a primary cause of glutamate-induced ROS formation in neuronal presynaptic terminals. Activation of NMDA receptors might be responsible for a certain part of glutamate pro-oxidant action. Most likely, sources of glutamate-induced ROS formation in neuronal presynaptic terminals are NADPH oxidase and NOS activation.     

Neurochemical pathways involved in the protective effects of nicotine and ethanol in preventing the development of Parkinson's disease: potential targets for the development of new therapeutic agents

In this short review, neurochemical targets are identified where nicotine, and possibly ethanol, may interact to prevent the occurrence of Parkinson's disease. These are (a) the nicotinic acetycholine receptors present in the nigrostriatal area or on the surface of microglia, (b) monoamine oxidases and (c) inducible nitric oxide synthase. If such induced changes can be verified in clinical studies, this may help in the design of new therapeutic drugs which may be of relevance to diminish the incidence and perhaps the progression of the debilitating condition of Parkinson's disease.