Nitric oxide. No endothelial NO

Expression of nitric oxide synthases in rat odontoblasts and the role of nitric oxide in odontoblastic differentiation of rat dental papilla cells

As precursor cells of odontoblasts, dental papilla cells (DPCs) form the dentin-pulp complex during tooth development. Nitric oxide (NO) regulates the functions of multiple cells and organ tissues, including stem cell differentiation and bone formation. In this paper, we explored the involvement of NO in odontoblastic differentiation. We verified the expression of NO synthase (NOS) in rat odontoblasts by nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) staining and immunohistochemistry in vivo. The expression of all three NOS isoforms in rat DPCs was confirmed by quantitative reverse-transcription polymerase chain reaction (qRT-PCR), immunofluorescence, and western blotting in vitro. The expression of neuronal NOS and endothelial NOS was upregulated during the odontoblastic differentiation of DPCs. Inhibition of NOS function by NOS inhibitor l-N^G -monomethyl arginine (L-NMMA) resulted in reduced formation of mineralized nodules and expression of dentin sialophosphoprotein (DSPP) and dentin matrix protein (DMP1) during DPC differentiation. The NO donor S-nitroso-N-acetylpenicillamine (SNAP, 0.1, 1, 10, and 100 μM) promoted the viability of DPCs. Extracellular matrix mineralization and odontogenic markers expression were elevated by SNAP at low concentrations (0.1, 1, and 10 μM) and suppressed at high concentration (100 μM). Blocking the generation of cyclic guanosine monophosphate (cGMP) with 1H-(1,2,4)oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ) abolished the positive influence of SNAP on the odontoblastic differentiation of DPCs. These findings demonstrate that NO regulates the odontoblastic differentiation of DPCs, thereby influencing dentin formation and tooth development.

Role of nitric oxide in orthodontic tooth movement (Review)

Nitric oxide (NO) is an ubiquitous signaling molecule that mediates numerous cellular processes associated with cardiovascular, nervous and immune systems. NO also plays an essential role in bone homeostasis regulation. The present review article summarized the effects of NO on bone metabolism during orthodontic tooth movement in order to provide insight into the regulatory role of NO in orthodontic tooth movement. Orthodontic tooth movement is a process in which the periodontal tissue and alveolar bone are reconstructed due to the effect of orthodontic forces. Accumulating evidence has indicated that NO and its downstream signaling molecule, cyclic guanosine monophosphate (cGMP), mediate the mechanical signals during orthodontic-related bone remodeling, and exert complex effects on osteogenesis and osteoclastogenesis. NO has a regulatory effect on the cellular activities and functional states of osteoclasts, osteocytes and periodontal ligament fibroblasts involved in orthodontic tooth movement. Variations of NO synthase (NOS) expression levels and NO production in periodontal tissues or gingival crevicular fluid (GCF) have been found on the tension and compression sides during tooth movement in both orthodontic animal models and patients. Furthermore, NO precursor and NOS inhibitor administration increased and reduced the tooth movement in animal models, respectively. Further research is required in order to further elucidate the underlying mechanisms and the clinical application prospect of NO in orthodontic tooth movement.

Reactive Oxygen Species and Pressure Ulcer Formation after Traumatic Injury to Spinal Cord and Brain

Traumatic injuries to the nervous system, including the brain and spinal cord, lead to neurological dysfunction depending upon the severity of the injury. Due to the loss of motor (immobility) and sensory function (lack of sensation), spinal cord injury (SCI) and brain injury (TBI) patients may be bed-ridden and immobile for a very long-time. These conditions lead to secondary complications such as bladder/bowel dysfunction, the formation of pressure ulcers (PUs), bacterial infections, etc. PUs are chronic wounds that fail to heal or heal very slowly, may require multiple treatment modalities, and pose a risk to develop further complications, such as sepsis and amputation. This review discusses the role of oxidative stress and reactive oxygen species (ROS) in the formation of PUs in patients with TBI and SCI. Decades of research suggest that ROS may be key players in mediating the formation of PUs. ROS levels are increased due to the accumulation of activated macrophages and neutrophils. Excessive ROS production from these cells overwhelms intrinsic antioxidant mechanisms. While short-term and moderate increases in ROS regulate signal transduction of various bioactive molecules; long-term and excessively elevated ROS can cause secondary tissue damage and further debilitating complications. This review discusses the role of ROS in PU development after SCI and TBI. We also review the completed and ongoing clinical trials in the management of PUs after SCI and TBI using different technologies and treatments, including antioxidants.

Tetrahydropalmatine triggers angiogenesis via regulation of arginine biosynthesis

Over a short span of two decades, the central role of angiogenesis in the treatment of wound healing, diverse cancers, nerve defect, vascular injury and several ophthalmic diseases has become evident. Tetrahydropalmatine, as the index component of Corydalis yanhusuo W. T. Wang, is inseparable from protecting cardiovascular system, yet its role in angiogenesis has been poorly characterized. We have demonstrated the binding potential of THP and VEGFR2 using molecular docking based on the clinical experience of traditional Chinese medicine in the pretest study. Here, we identified tetrahydropalmatine (THP) as one proangiogenic trigger via regulation of arginine biosynthesis by pharmacological assays and DESI-MSI/GC-MS based metabolomics. First, the proangiogenic effects of THP were evaluated by quail chorioallantoic membrane test in vivo and multiple models of endothelial cells in vitro. According to virtual screening, the main mechanisms of THP (2/5 of the top terms with smaller p-value) were metabolic pathways. Hence, metabolomics was applied for the main mechanisms of THP and results showed the considerable metabolite difference in arginine biosynthesis (p < 0.05) altered by THP. Finally, correlated indicators were deteced using targeted metabolomics and pharmacological assays for validation, and results suggested the efficacy of THP on citrulline to arginine flux, arginine biosynthesis, and endothelial VEGFR2 expression sequentially, leading to the promotion of angiogenesis. Overall, this manuscript identified THP as the proangiogenic trigger with the potential to develop as pharmacological agents for unmet clinical needs.

Cell-specific expression and immunolocalization of nitric oxide synthase isoforms and the related nitric oxide/cyclic GMP signaling pathway in the ovaries of neonatal and immature rats

OBJECTIVE

The present study is designed to investigate the cellular expressions and immunolocalizations of three different nitric oxide synthase (NOS) isoforms and the related nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway in the ovaries of neonatal and immature rats.

METHODS

The ovaries were obtained from ICR (Institute for Cancer Research) female Sprague-Dawley rats at postnatal days 1, 5, 7, 10, and 19. Then we carried out the histologic examination, immunohistochemistry, measurement of NOS activity, and modifications within the NO/cGMP pathway.

RESULTS

During postnatal days 1, 5, 7, 10, and 19, all three isoforms of NOS were mainly localized to the oocytes and expressed as a gradual increase in granulosa cells and theca cells within the growing follicle. The ovarian total NOS activities and NO levels were increased at postnatal days 7 and 10 compared with other days.

CONCLUSIONS

Our findings suggest that the locally produced NO and the NO/NOS signaling systems are involved in the follicular development to puberty.

Leukocytes: essential cells in ovarian function and ovulation

The disciplines of reproduction and immunology, once quite discrete, are now closely associated, with compelling evidence to suggest that immune mechanisms play important roles in the cervix, uterus, fallopian tubes and ovary. Cells and mediators classically described as part of the immune system are found throughout the reproductive tract. Disorders of reproduction, including pre-eclampsia, unexplained infertility, endometriosis, recurrent miscarriage and disturbed fetal growth almost certainly have some of their origins in the dysfunction of immune regulation. There appears to be some evidence that immune disorders, such as rheumatoid arthritis and scleroderma, can manifest as infertility, before clinical disease becomes apparent.

Involvement of nitric oxide synthase in the mechanism of histamine-induced inhibition of Leydig cell steroidogenesis via histamine receptor subtypes in Sprague-Dawley rats

This study was conducted to shed light on the so far unexplored intracellular mechanisms underlying negative modulation of Leydig cell steroidogenesis by histamine (HA). Using the MA-10 cell line and highly purified rat Leydig cells as experimental models, we examined the effect of the amine on biochemical steps known to be modulated by HA or involved in LH/hCG action. In agreement with previous findings, HA at 10 microM showed a potent inhibitory effect on hCG-stimulated steroid synthesis, regardless of the gonadotropin concentration used. Moreover, HA decreased not only LH/hCG-induced cAMP production but also steroid synthesis stimulated by the permeable cAMP analog dibutyryl cAMP (db-cAMP). Considering the post-cAMP sites of HA action, it is shown herein that HA markedly inhibited db-cAMP-stimulated steroidogenic acute regulatory (STAR) protein expression, as well as steps catalyzed by P450-dependent enzymes, mainly the conversion of cholesterol to pregnenolone by cholesterol side-chain cleavage enzyme (CYP11A). The antisteroidogenic action of HA was blocked by addition of the phospholipase C (PLC) inhibitor U73122, and HA significantly augmented inositol triphosphate (IP3) production, suggesting a major role for the PLC/IP3 pathway in HA-induced inhibition of Leydig cell function. Finally, HA increased nitric oxide synthase (NOS) activity, and the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) markedly attenuated the effect of the amine on steroid synthesis. On the basis of our findings, HA antagonizes the gonadotropin action in Leydig cells at steps before and after cAMP formation. NOS activation is the main intracellular mechanism by which HA exerts its antisteroidogenic effects.

Cardiovascular roles of nitric oxide: a review of insights from nitric oxide synthase gene disrupted mice

Nitric oxide (NO) is a gaseous molecule that plays many key roles in the cardiovascular system. Each of the enzymes that generate NO--neuronal, inducible and endothelial NO synthase-has been genetically disrupted in mice. This review discusses the cardiovascular phenotypes of each of the NO synthase (NOS) gene knockout mice, and the insights gained into the roles of NO in the cardiovascular system. Mice lacking the endothelial isoform are hypertensive, have endothelial dysfunction and show a more severe outcome in response to vascular injury, to stroke and cerebral ischaemia, and to diet-induced atherosclerosis. Mice lacking the neuronal isoform show a less severe outcome in response to stroke and cerebral ischaemia but have increased diet-induced atherosclerosis. Mice lacking the inducible isoform show reduced hypotension to septic shock. Together, NOS gene knockout mice have been useful tools that complement our other approaches to studying the multiple roles of NO in the cardiovascular system.

Integrin stimulation-induced hypertrophy in neonatal rat cardiomyocytes is NO-dependent

Prolonged myocardial stretch typically leads to hypertrophy of cardiomyocytes. As integrins are cellular receptors of stretch, we hypothesize that integrin stimulation induces cardiomyocyte hypertrophy. Integrins of neonatal rat cardiomyocytes (NRCMs) were stimulated with a peptide containing the Arg-Gly-Asp (RGD) sequence for 24 h. For comparison, alpha(1)-adrenergic stimulation by phenylephrine (PE) for 24 h was applied. Saline-treated NRCMs were used as control. The hypertrophic response was quantified by measuring cell surface area (CSA). Phosphorylation of NO-synthase-1 (NOS1) was assessed by immunocytochemistry. CSA was increased by 38% (IQR 31-44%) with RGD and by 68% (IQR 64-84%) with PE versus control (both P < 0.001). NOS-1 phosphorylation was increased by 61% with RGD and by 21% with PE versus control (both P < 0.01). A general NOS-inhibitor (L-NAME) inhibited RGD-induced hypertrophy completely, but had no significant effect on PE-induced hypertrophy. Administration of NO-donor to NRCMs co-incubated with RGD + L-NAME partly restored hypertrophy (to 62% of the hypertrophic effect of RGD alone), but had no effect if incubated with PE + L-NAME. Ryanodine and BAPTA-AM inhibited RGD-induced hypertrophy completely but not that induced by PE. Integrin stimulation of NRCMs by RGD leads to hypertrophy, likely by activation of NOS-1. Abrogation of RGD-induced hypertrophic response upon NOS-inhibition and rescue of this hypertrophic effect by NO-donor suggest that integrin stimulation-induced hypertrophy of NRCMs is NO-dependent.

Influence of nitric oxide during maturation on bovine oocyte meiosis and embryo development in vitro

The effect of s-nitroso-n-acetyl-l,l-penicillamine (SNAP, a nitric oxide donor) during in vitro maturation (IVM) on nuclear maturation and embryo development was investigated. The effect of increasing nitric oxide (NO) during prematuration or maturation, or both, on embryo development was also assessed. 10–3 m SNAP nearly blocked oocytes reaching metaphase II (MII) (7%, P < 0.05) while 10–5 m SNAP showed intermediate proportions (55%). For 10–7 m SNAP and controls (without SNAP), MII percentages were similar (72% for both, P > 0.05), but superior to the other treatment groups (P < 0.05). Blastocyst development, however, was not affected (38% for all treatments, P < 0.05). TUNEL-positive cells in hatched blastocysts (Day 9) increased when IVM included 10–5 m SNAP (8 v. 3 to 4 cells in the other treatments, P > 0.05), without affecting total cell numbers (240 to 291 cells, P > 0.05). When oocytes were prematured followed by IVM with or without 10–7 m SNAP, during either culture period or both, blastocyst development was similar (26 to 40%, P > 0.05). When SNAP was included during both prematuration and IVM, the proportion of Day 9 hatched embryos increased (28% v. 14 to 19% in the other treatments, P < 0.05). Apoptotic cells, however, increased when SNAP was included (6 to 10 cells) in comparison to prematuration and maturation without SNAP (3 cells, P < 0.05). NO may be involved in meiotic progression and apoptosis during embryo development.

Endometrial nitric oxide production and nitric oxide synthases in the equine endometrium: Relationship with microvascular density during the estrous cycle

Nitric oxide (NO) plays an important role in angiogenesis and in the regulation of the blood flow. This study was carried out to investigate (i) the effects of endogenous estrogens and progestins and exogenous progesterone (P(4)) (5 ng/ml or 1 microg/ml) or estradiol 17beta (E(2)beta) (50 pg/ml or 1 microg/ml) on in vitro endometrial NO synthesis; (ii) the presence of different isoforms of NO synthase; (iii) and their relationship to microvascular density in the equine endometrium during the estrous cycle. NOS expression was also evaluated in the myometrium. Expression of endothelial and inducible forms of NOS in the uterus was assessed by Western blot and immunocytochemistry. Vascular density in endometrial tissue was determined on histologic sections. In the luteal phase, compared to the follicular phase, endometrial NO production increased without exogenous hormones and with exogenous E(2)beta (1 microg/ml). Although immunocytochemistry revealed iNOS and eNOS expression in the endometrium, no positive signal for iNOS was detected by Western blot. Endothelial NOS was observed in endometrial glands, endothelial cells, fibroblasts, blood and lymphatic vessels. Endometrial eNOS expression was the highest in the follicular and mid-luteal phases while it was found to be the lowest in the early luteal phase. In the follicular phase, hyperplasia of endometrial tissue with respect to myometrium was detected. No difference in vascular density was present between phases. All together, NO may play some roles in both proliferative and secretory phases of endometrial development in the mare.

d-Aspartic acid and nitric oxide as regulators of androgen production in boar testis

D-Aspartic acid (D-Asp) and nitric oxide (NO) are two biologically active molecules playing important functions as neurotransmitters and neuromodulators of nerve impulse and as regulators of hormone production by endocrine organs. We studied the occurrence of D-Asp and NO as well as their effects on testosterone synthesis in the testis of boar. This model was chosen for our investigations because it contains more Leydig cells than other mammals. Indirect immunofluorescence applied to cryostat sections was used to evaluate the co-localization of D-Asp and of the enzyme nitric oxide synthase (NOS) in the same Leydig cells. D-Asp and NOS often co-existed in the same Leydig cells and were found, separately, in many other testicular cytotypes. D-Asp level was dosed by an enzymatic method performed on boar testis extracts and was 40+/-3.6 nmol/g of fresh tissue. NO measurement was carried out using a biochemical method by NOS activity determination and expressed as quantity of nitrites produced: it was 155.25+/-21.9 nmol/mg of tissue. The effects of the two molecules on steroid hormone production were evaluated by incubating testis homogenates, respectively with or without D-Asp and/or the NO-donor L-arginine (L-Arg). After incubation, the testosterone presence was measured by immunoenzymatic assay (EIA). These in vitro experiments showed that the addition of D-Asp to incubated testicular homogenates significantly increased testosterone concentration, whereas the addition of L-Arg decreased the hormone production. Moreover, the inclusion of L-Arg to an incubation medium of testicular homogenates with added D-Asp, completely inhibited the stimulating effects of this enantiomer. Our results suggest an autocrine action of both D-Asp and NO on the steroidogenetic activity of the Leydig cell.

Brain natriuretic peptide limits myocardial infarct size dependent of nitric oxide synthase in rats

BACKGROUND

Brain natriuretic peptide (BNP) has recently been shown to have a cardioprotective effect in animal models of myocardial ischemia-reperfusion (I-R) injury. We hypothesized that exogenous BNP limits myocardial infarction on nitric oxide synthase pathway.

METHODS

A rat model of myocardial I-R injury was established by ligating the left descending coronary artery for 30 min and then reperfusing for 2 h. BNP was injected with different dose 5 min after the ligation and lasting for 145 min. The myocardial infarct size and the area at risk of ischemia were measured by staining with triphenyltetrazolium chloride (TTC) and Evans blue dye. To examine the role of nitric oxide synthase (NOS), expression of eNOS in the left ventricle was analyzed by western blotting. Nomega-nitro-L-arginine methyl ester (L-NAME; 30 ug/kg), or S-methylisothiourea (SMT; 3 ug/kg) was administrated before I-R with or without BNP.

RESULTS

The control infarct-to-risk ratio was 45.1+/-1.72% (means+/-SE). BNP infused 5 min after ischemia limited infarct size in a dosage-dependent manner, with maximal protection observed at 0.01 ug/(kg min) (infarct-to-risk: 24.7+/-1.69%, P<0.01 vs. control), associated with a 10-fold increase of myocardial endothelial nitric oxide synthase above the control value. Protection afforded by BNP was abolished by L-NAME but not by SMT, suggesting the involvement of putative endothelial but not inducible nitric oxide synthase activation.

CONCLUSIONS

We conclude that natriuretic peptide/NOS/NO signaling may constitute an important injury-limiting mechanism in myocardium.

Nitric Oxide Induces Apoptosis in Bovine Luteal Cells

We previously showed in in vivo and in vitro studies that nitric oxide (NO) is engaged in luteolysis in cattle. Nitric oxide produced locally in the bovine corpus luteum (CL) inhibits progesterone (P4) synthesis and is suggested to be a component of the luteolytic cascade induced by uterine prostaglandin (PG) F2alpha. In the present study, the molecular mechanisms of NO action during structural luteolysis were studied in cultured bovine luteal cells (Days 15-17 of the estrous cycle). The effects of the NO donor (NONOate; 10(-4)M) on DNA fragmentation, cell viability, P4 production and caspase-3 activity were compared with those of PGF2alpha (10(-6)M). Moreover, mobilization of intracellular calcium [Ca2+]i and gene expressions of Fas-L, Fas, bcl-2, bax, and caspase-3 in the cells were determined by semi-quantitative RT-PCR after NONOate treatment. Caspase-3 activity was examined calorimetrically. Contrary to PGF2alpha NONOate decreased cell viability. DNA fragmentation after NONOate treatment increased by more than with PGF22alpha. NONOate increased mobilization of [Ca2+]i in the cells. Although the NO donor did not affect Fas-L and bcl-2 gene expression, it stimulated Fas and bax mRNA and caspase-3 expression. The ratio of bcl-2 to bax mRNA level decreased in the cells treated with NONOate. Moreover, NONOate stimulated caspase-3 activity more effectively than PGF2alpha. The overall results suggest that NO is a luteolytic factor that plays a crucial role in regulation of the estrous cycle in structural luteolysis by inducing apoptosis of luteal cells in cattle.

Inhibition of α7-nicotinic acetylcholine receptor expression by arsenite in the vascular endothelial cells

The alpha7-nicotinic acetylcholine receptor (alpha7-nAChR), expressed in the neuronal and non-neuronal cells, has been shown to regulate cell proliferation. However, the expression and function of the alpha7-nAChR in the proliferation of the vascular endothelial cells remain unclear. In this study, we investigated the expression of the alpha7-nAChR in the arsenite-exposed vascular endothelial cells. The vascular endothelial cells SVEC4-10 and porcine aorta endothelial cells (PAEC) expressed the alpha7-nAChR proteins. Moreover, the location of the alpha7-nAChR proteins on cell membrane of the vascular endothelial cells was identified by the alpha7-nAChR binding to a tetramethylrhodamine-labeled alpha-bungarotoxin (alpha-BTX). Arsenite (20 microM, 24 h) significantly induced the cytotoxicity, cell growth inhibition, and apoptosis in the vascular endothelial cells. The level of alpha7-nAChR proteins was concentration dependently decreased in the arsenite-treated endothelial cells. Furthermore, a specific alpha7-nAChR antagonist, alpha-BTX, inhibited the cell viability in the vascular endothelial cells. Nevertheless, alpha-BTX, and a alpha7-nAChR agonist, nicotine, did not significantly alter the cytotoxicity in the arsenite-treated endothelial cells. In addition, arsenite decreased the level of endothelial nitric oxide synthase proteins but did not alter choline acetyltransferase proteins in the SVEC4-10 endothelial cells. Together, our results indicate that arsenite can inhibit the alpha7-nAChR protein expression and cause the cell injury in the vascular endothelial cells.

Contribution of Akt and endothelial nitric oxide synthase to diazoxide-induced late preconditioning

The opening of mitochondrial ATP-sensitive K+ (mitoKATP) channels has a significant role in delayed ischemic preconditioning, and nitric oxide (NO) is a well-known trigger for its activation. However, the source of NO remains unknown. Phosphorylation of endothelial NO synthase (eNOS) increases NO production and reduces apoptosis through the Akt signaling pathway. To elucidate the Akt signaling pathway involved in the opening and antiapoptotic effect of mitoKATP channel during delayed pharmacological preconditioning, the mitoKATP channel opener diazoxide (DE, 7 μg/kg ip) alone or DE plus Nω-nitro-l-arginine methyl ester (l-NAME, 30 μg/kg iv), an inhibitor of NOS, or wortmannin (WTN, 15 μg/kg iv), an inhibitor of phosphatidylinositol 3′-kinase (PI3 kinase), was administered to wild-type (WT) or eNOS−/− mice during DE treatment. Twenty-four hours later, hearts were isolated and subjected to 40 min ischemia and 30 min reperfusion (I/R). The effect of DE and other interventions on hemodynamic, terminal dUTP nick-end labeling staining and biochemical changes during I/R was assessed in mouse hearts. Treatment with DE resulted in a 2.2-fold increase in phosphorylation of Akt and a significant increase in eNOS and inducible NOS (iNOS) proteins. Akt is upstream of NOS and the mitoKATP channel as simultaneous pretreatment of WTN with DE abolished phosphorylation of Akt, which was not affected by l-NAME and 5-hydroxydecanoate. In hearts treated with DE, cardiac function was significantly improved after I/R, and apoptosis was also significantly decreased. WTN abolished the antiapoptotic effect of DE. Similarly, S-methylisothiourea, a specific iNOS inhibitor, when given to eNOS−/− mice that were pretreated with DE completely abolished the beneficial effects of DE on reduction of apoptotic death. DE was partially effective in eNOS−/− mice against the ischemic injury. It is concluded that DE activates Akt through the PI3 kinase signaling pathway and iNOS and eNOS is downstream of Akt.

The beta1 subunit of the Ca2+-sensitive K+ channel protects against hypertension

Previous animal studies have demonstrated that the loss of the beta(1) subunit of the large-conductance Ca(2+)-activated K(+) (BK) channel leads to hypertension. A new study demonstrates that a gain in beta(1) subunit function is associated with protection against diastolic hypertension in humans, underscoring the importance of the beta(1) subunit and the BK channel in the regulation of vascular resistance.

Theoretical approach to description of time-dependent nitric oxide effects in the vasculature

Nitric oxide (NO) is one of the most important signal compounds in a living cell. As a typical free radical it has both toxic and physiological effects and their balance is determined by a spatial distribution of NO concentration. Moreover, some biological functions, especially NO-mediated relaxation of blood vessels, have to be time-limited. In order to circumscribe this phenomenon non steady-state mathematical model has been used for description of nitric oxide diffusion in vascular smooth muscle. It was shown that the microvascular relaxation could be observed even after a short time of NO production in the endothelium. This time is up to 3 times below that needed to reach the steady-state spatial NO gradient. However, the effect of nitric oxide essentially depends on the rate of NO production and blood vessel diameter. Furthermore, non steady-state nitric oxide concentration gradient was represented as an analytical function of time and coordinate. It is essential that this function describes a common case of one-dimensional diffusion of uncharged low-mass molecules. Thus, the results can be used for calculation of an upper estimation of experimental data.

Steroid hormones augment nitric oxide synthase activity and expression in rat uterus

Nitric oxide (NO) is synthesized in a variety of tissues, including rat uterus, from L-arginine by NO synthase (NOS), of which there are three isoforms, namely neuronal, endothelial and inducible NOS (nNOS, eNOS and iNOS, respectively). Nitric oxide is an important regulator of the biology and physiology of the organs of the reproductive system, including the uterus. Some studies have shown increased variation in NO production and NOS expression during the oestrous cycle. However, the factors that regulate NO production in the uterus remain unclear. Therefore, in the present study, we investigated the effect of sex steroids on NOS expression and activity in the ovariectomized rat uterus. Ovariectomized rats received progesterone (4 mg per rat) or 17β-oestradiol (1 μg per rat). All rats were killed 18 h after treatment. Both progesterone and oestradiol were able to augment NOS activity. The effect of oestradiol was abolished by pre-incubation with 500 μM aminoguanidine, an iNOS inhibitor, or by coadministration of oestradiol with 3 mg kg−1 dexamethasone, but the effect of progesterone was not affected by these treatments. Uterine nNOS, eNOS and iNOS protein levels were assessed using Western blots. Ovariectomized rat uteri expressed iNOS and eNOS. Progesterone increased the expression of eNOS and iNOS, whereas oestradiol increased iNOS expression only. These results suggest that oestradiol and progesterone are involved in the regulation of NOS expression and activity during pregnancy and implantation in the rat.

Carbon monoxide and the nervous system

Carbon monoxide (CO) is a colorless, tasteless, odorless, and non-irritating gas formed when carbon in fuel is not burned completely. It enters the bloodstream through the lungs and attaches to hemoglobin (Hb), the body's oxygen carrier, forming carboxyhemoglobin (COHb) and thereby reducing oxygen (O(2)) delivery to the body's organs and tissues. High COHb concentrations are poisonous. Central nervous system (CNS) effects in individuals suffering acute CO poisoning cover a wide range, depending on severity of exposure: headache, dizziness, weakness, nausea, vomiting, disorientation, confusion, collapse, and coma. At lower concentrations, CNS effects include reduction in visual perception, manual dexterity, learning, driving performance, and attention level. Earlier work is frequently cited to justify the statement that CO exposure sufficient to produce COHb levels of ca. 5% would be sufficient to produce visual sensitivity reduction and various neurobehavioral performance deficits. In a recent literature re-evaluation, however, the best estimate was that [COHb] would have to rise to 15-20% before a 10% reduction in any behavioral or visual measurement could be observed. This conclusion was based on (1) critical review of the literature on behavioral and sensory effects, (2) review and interpretation of the physiological effects of COHb on the CNS, (3) extrapolation from the effects of hypoxic hypoxia to the effects of CO hypoxia, and (4) extrapolation from rat behavioral effects of CO to humans. Also covered in this review article are effects of chronic CO exposure, the discovery of neuroglobin, a summary of the relatively new role for endogenous CO in neurotransmission and vascular homeostasis, groups which might be especially sensitive to CO, and recommendations on further research. The interested reader is directed to other published reviews of the literature on CO and historically seminal references that form our understanding of this ubiquitous gas.

Endothelial nitric oxide synthase (NOS) deficiency affects energy metabolism pattern in murine oxidative skeletal muscle

Oxidative capacity of muscles correlates with capillary density and with microcirculation, which in turn depend on various regulatory factors, including NO generated by endothelial nitric oxide synthase (eNOS). To determine the role of eNOS in patterns of regulation of energy metabolism in various muscles, we studied mitochondrial respiration in situ in saponin-permeabilized fibres as well as the energy metabolism enzyme profile in the cardiac, soleus (oxidative) and gastrocnemius (glycolytic) muscles isolated from mice lacking eNOS (eNOS(-/-)). In soleus muscle, the absence of eNOS induced a marked decrease in both basal mitochondrial respiration without ADP (-32%; P <0.05) and maximal respiration in the presence of ADP (-29%; P <0.05). Furthermore, the eNOS(-/-) soleus muscle showed a decrease in total creatine kinase (-29%; P <0.05), citrate synthase (-31%; P <0.01), adenylate kinase (-27%; P <0.05), glyceraldehyde-3-phosphate dehydrogenase (-43%; P <0.01) and pyruvate kinase (-26%; P <0.05) activities. The percentage of myosin heavy chains I (slow isoform) was significantly increased from 24.3+/-1.5% in control to 30.1+/-1.1% in eNOS(-/-) soleus muscle ( P <0.05) at the expense of a slight non-significant decrease in the three other (fast) isoforms. Besides, eNOS(-/-) soleus showed a 28% loss of weight. Interestingly, we did not find differences in any parameters in cardiac and gastrocnemius muscles compared with respective controls. These results show that eNOS knockout has an important effect on muscle oxidative capacity as well on the activities of energy metabolism enzymes in oxidative (soleus) muscle. The absence of such effects in cardiac and glycolytic (gastrocnemius) muscle suggests a specific role for eNOS-produced NO in oxidative skeletal muscle.

Effects of chronic nicotine administration on nitric oxide synthase expression and activity in rat brain

Although there is substantial evidence concerning the influence of nicotine on nitric oxide (NO) synthesis in the vascular system, there are fewer studies concerning the central nervous system. Although NO metabolites (nitrates/nitrites) increase in several rat brain regions after chronic injection of nicotine, the cellular origin of this rise in NO levels is not known. The aim of the present work was to assess the effects of repetitive nicotine administration on nitric oxide synthase (NOS) expression and activity in male and female rat brains. To determine levels of nitrate/nitrite, the Griess reaction was carried out in tissue micropunched from the frontal cortex, striatum, and accumbens of both male and female rats untreated (naïve) or injected with saline or nicotine (0.4 mg/kg for 15 days). In parallel, coronal sections of fixed brains from equally treated animals were immunostained for neuronal NOS or histochemically labelled for NADPH-diaphorase activity. Nicotine treatment increased NO metabolites significantly in all brain regions compared with naïve or saline-treated rats. By contrast, analysis of the planimetric counting of NOS/NADPH-diaphorase-positive neurons failed to demonstrate any significant effect of the nicotine treatment. A significant decrease was observed with both techniques employed in saline-injected female rats compared with naïve animals, suggesting a stress response. The mismatch between the biochemical and the histological data after chronic nicotine treatment is discussed. The up-regulation of NO sources other than neurons is proposed.

Loss of heterozygosity of the NOS3 dinucleotide repeat marker in atherosclerotic plaques of human carotid arteries

We have investigated 28 atherosclerotic plaques of human carotid arteries with a panel of 39 microsatellite markers for the presence of LOH. The objective of this research was to verify if LOH, described in association with tumorigenic process, could be involved also in benign fibroproliferative disease. Seventy percent of samples demonstrated allelic imbalance: 50% of cases showed LOH at a minimum of one locus, 3.5% at a minimum of two loci and 14.3% at three or more loci. The percentages of LOH ranged between 3.8 and 14.3% and the highest involved polymorphic marker is the NOS3 internal dinucleotide repeat. Our results indicate that, like tumorigenesis, the atherogenic process could also involve LOH mechanism. Furthermore, the finding regarding the NOS3 internal polymorphism suggests a possible role of the gene as cofactor in formation of the atheromas.

Reproductive function in female mice lacking the gene for endothelial nitric oxide synthase

Nitric oxide (NO) acts as a neuronal messenger in both the central and peripheral nervous systems and has been implicated in reproductive physiology and behavior. Pharmacological inhibition of nitric oxide synthase (NOS) with the nonspecific NOS inhibitor, l-N(G)-nitro-Arg-methyl ester (l-NAME), induced deficits in both the number of ovarian rupture sites and the number of oocytes recovered in the oviducts of mice. Female neuronal NOS knockout (nNOS-/-) mice have normal numbers of rupture sites, but reduced numbers of oocytes recovered following systemic injections of gonadotropins, suggesting that NO produced by nNOS accounts, in part, for deficits in ovulatory efficiency observed after l-NAME administration. Additionally, endothelial NOS knockout (eNOS-/-) mice have reduced numbers of ovulated oocytes after superovulation. Because endothelial NOS has been identified in ovarian follicles, and because of the noted reduced breeding efficiency of eNOS-/- mice, the present study sought to determine the role of NO from eNOS in mediating the number of rupture sites present after ovulation. Estrous cycle length and variability were consistently reduced in eNOS-/- females. The number of rupture sites was normal in eNOS-/- mice under natural conditions and after administration of exogenous GnRH. After exogenous gonadotropin administration, eNOS-/- females displayed a significant reduction in the number of ovarian rupture sites. Female eNOS-/- mice also produced fewer pups/litter compared to WT mice. These data suggest that NO from endothelial sources might play a role in mediating rodent ovulation and may be involved in regulation of the timing of the estrous cycle.

Morphological relations between haem oxygenases, NO-synthase and VIP in the canine and feline gastrointestinal tracts

Carbon monoxide (CO), produced by haem oxygenase (HO), has been suggested as a messenger molecule in the central and peripheral nervous systems. In the present study, we have investigated the occurrence of the two isoforms of HO, HO-2 and HO-1 in the canine and feline gastrointestinal tracts, including the small and large intestine and the gastrointestinal sphincters. An abundance of nerve cell bodies that contained immunoreactivity for HO-2 was found in the submucosal and myenteric plexuses. HO-2 immunoreactivity was frequently co-localized with nitric oxide synthase (NOS) or vasoactive intestinal peptide (VIP) immunoreactivities and was also observed in some nerve fibres, certain non-neuronal cells dispersed among smooth muscle bundles, and in vascular endothelium. The antiserum against HO-1 revealed immunoreactivity in nerve cell bodies in the enteric plexuses, in nerve fibres and in non neuronal cells in the smooth muscle layers. Some of the nerve structures were also NOS- or VIP-immunoreactive. These results demonstrate the presence of HO isoenzymes in nerves and other structures of the canine and feline gastrointestinal tracts and support the view that CO may have a role as a messenger molecule in the enteric nervous system.

Nitric oxide signaling in invertebrates

Nitric oxide (NO) is an unconventional neurotransmitter and neuromodulator molecule that is increasingly found to have important signaling functions in animals from nematodes to mammals. NO signaling mechanisms in the past were identified largely through experiments on mammals, after the discovery of NO's vasodilatory functions. The use of gene knock out mice has been particularly important in revealing the functions of the several isoforms of nitric oxide synthase (NOS), the enzyme that produces NO. Recent studies have revealed rich diversity in NO signaling. In addition to the well-established pathway in which NO activates guanylyl cyclase and cGMP production, redox mechanisms involving protein nitrosylation are important contributors to modulation of neurotransmitter release and reception. NO signaling studies in invertebrates are now generating a wealth of comparative information. Invertebrate NOS isoforms have been identified in insects and molluscs, and the conserved and variable amino acid sequences evaluated. Calcium-calmodulin dependence and cofactor requirements are conserved. NADPH diaphorase studies show that NOS is found in echinoderms, coelenterates, nematodes, annelids, insects, crustaceans and molluscs. Accumulating evidence reveals that NO is used as an orthograde transmitter and cotransmitter, and as a modulator of conventional transmitter release. NO appears to be used in diverse animals for certain neuronal functions, such as chemosensory signaling, learning, and development, suggesting that these NO functions have been conserved during evolution. The discovery of NO's diverse and unconventional signaling functions has stimulated a plethora of enthusiastic investigations into its uses. We can anticipate the discovery of many more interesting and some surprising NO signaling functions.

Chronic administration of cyclosporine A does not impair memory retention in rats

Cyclosporine A (CsA) is the treatment of choice for patients undergoing organ as well as neural transplantation. CsA immunosuppression is associated with neurological and motor alterations in transplant recipients as well as in normal or hemiparkinsonian rats. We investigated possible impairments of memory retention in CsA-treated rats to determine direct effects of CsA on the dementing illness inherent in most neurodegenerative disorders. Rats receiving chronic treatment with CsA at a dose of 10 mg kg-1, i.p., daily for 26 days, as used in neural transplants for animal models of neurodegenerative disorders did not significantly differ from vehicle-treated rats, and even appeared slightly improved, in retention of a passive avoidance task. This present observation parallels recent studies demonstrating 'neuroprotective' effects of CsA in addition to its immunosuppressive effects.

Substrate binding and calmodulin binding to endothelial nitric oxide synthase coregulate its enzymatic activity

Endothelial nitric oxide synthase (NOS) is a constitutively expressed flavin-containing heme protein that catalyzes the formation of NO from L-arginine, NADPH, and molecular oxygen. We purified bovine endothelial NOS from transfected embryonic kidney cells by conventional chromatographic techniques and characterized the activity of the detergent-solubilized enzyme. Endothelial NOS displays a much lower specific activity of NO synthesis (143 +/- 11 nmol NO/min/mg enzyme) than the constitutive neuronal NOS or inducible NOS isoforms. Like the neuronal isoform, endothelial NOS requires binding of Ca2+/calmodulin to achieve Vmax NO synthase activity; however, we observed a basal level of NO synthesis even when Ca2+/calmodulin was omitted and 0.5 mM EDTA was present in the assay solution. Moreover, endothelial NOS demonstrates a high-affinity bonding interaction with calmodulin such that the enzyme as purified has a NO synthase activity at about 80% of Vmax. We also observed a more than twofold increase in NADPH consumption by endothelial NOS when it was coupled to arginine oxygenation as opposed to when oxygen is activated in the absence of substrate. Substrate binding was also shown to stimulate heme reduction in the absence of added calmodulin. Thus, the enzymatic synthesis of NO from L-arginine by endothelial NOS appears to be partially regulated by binding of both calmodulin and substrate. These findings for endothelial NOS represent a significant departure from the enzymatic properties of the other constitutive NOS isoform, neuronal NOS, and we interpret this result in terms of the physiological implications.

Enlarged infarcts in endothelial nitric oxide synthase knockout mice are attenuated by nitro-L-arginine

Infarct size and vascular hemodynamics were measured 24 h after middle cerebral artery (MCA) occlusion in mice genetically deficient in the endothelial nitric oxide synthase (eNOS) isoform. eNOS mutant mice developed larger infarcts (21%) than the wild-type strain when assessed 24 h after intraluminal filament occlusion. Moreover, regional CBF values recorded in the MCA territory by laser-Doppler flowmetry were more severely reduced after occlusion and were disproportionately reduced during controlled hemorrhagic hypotension in autoregulation experiments. Unlike the situation in wild-type mice, nitro-L-arginine superfusion (1 mM) dilated pial arterioles of eNOS knockout mice in a closed cranial window preparation. As noted previously, eNOS mutant mice were hypertensive. However, infarct size remained increased despite lowering blood pressure to normotensive levels by hydralazine treatment. Systemic administration of nitro-L-arginine decreased infarct size in eNOS mutant mice (24%) but not in the wild-type strain. This finding complements published data showing that nitro-L-arginine increases infarct size in knockout mice expressing the eNOS but not the neuronal NOS isoform (i.e., neuronal NOS knockout mice). We conclude that NO production within endothelium may protect brain tissue, perhaps by hemodynamic mechanisms, whereas neuronal NO overproduction may lead to neurotoxicity.

Conserved Glu318 at the cytochrome P450 1A2 distal site is crucial in the nitric oxide complex stability

Nitric oxide synthase (NOS) has a thiolate-coordinated heme active site similar to that of cytochrome P450 (P450). Both NOS and P450 form stable nitric oxide (NO)-ferric heme complexes, whereas an NO-ferric heme complex of methemoglobin, that has an imidazole-coordinated heme active site, is easily reduced. The NO complex stability of the thiolate-coordinated hemoproteins, however, appeared irreconcilable with the strong electron-donating capability of the cysteine thiolate. In the present study, NO bindings to cytochrome P450 1A2 (P450 1A2) distal mutants were studied in the presence of various substrates. We found that a mutation at Glu-318 to Ala in the putative distal site of P450 1A2, suggested to be important in the O2 activation of P450 reactions, markedly facilitates the reduction of the NO-ferric complex. Addition of 1,2:3,4-dibenzanthracene or phenanthrene almost abolished the mutation effect on the NO complex. Based on these results, together with other spectral and kinetic data, it is suggested that the NO-ferric complex stability of P450, and perhaps of NOS, is largely ascribed to an ionic bridge between NO and the distal carboxyl group.

Physiological and pathophysiological roles of nitric oxide in the central nervous system

Nitric oxide (NO) is produced by three distinct isoforms of nitric oxide synthases in the central nervous system. Here, the roles of nitric oxide in the central nervous system are reviewed under physiological and pathophysiological conditions. Under physiological conditions, NO plays a role in the regulation of cerebral blood flow and autoregulation, blood flow-metabolism coupling, neurotransmission, memory formation, modulation of neuroendocrine functions, and behavioral activity. Impairment of the NO-mediated cerebrovascular vasodilatation occurs during ischemia-reperfusion, diabetes, hypertension, subararchnoid hemorrhage, and various forms of shock. Enhancement of NO production in the brain occurs during stoke, seizures, and acute and chronic inflammatory and neurodegenerative disorders. The alterations of the expression of the various isoforms of nitric oxide synthases under the above conditions are discussed. Moreover, the molecular mechanisms of NO and peroxynitrite induced cellular injury are delineated. Finally, the current strategies available for selective pharmacological manipulation of individual nitric oxide synthase isoforms are discussed.

Peroxynitrite inhibition of nitric oxide synthases

Peroxynitrite (PN) can be formed under mainly pathophysiological conditions from nitric oxide (NO) and superoxide anion and may be responsible for oxidative modifications of biomolecules. Preparations of nitric oxide synthases from porcine cerebellum (nNOS), bovine aortic endothelium (eNOS) and cytokine-treated murine macrophages (iNOS) were inhibited by PN in their ability to transform arginine to citrulline and nitric oxide with IC50 values of 15, 28, and 10 microM, respectively. Glutathione, bovine serum albumin and tyrosine provided varying degrees of protection in the three preparations. Intact endothelial cells, upon exposure to PN, rapidly lost their glutathione content but protein-SH groups and eNOS activity remained largely unaffected. Destruction of the heme-thiolate catalytic site was observed when nNOS was exposed to PN suggesting that the irreversible oxidation of this bond may be the common mechanism of NOS inhibition.