Two week nicotine treatment selectively increases bone vascular constriction in response to norepinephrine

Nicotine and vascular dysfunction

Cigarette smoking is the single most important risk factor for the development of cardiovascular diseases (CVDs). However, the role of nicotine, the addictive component of all tobacco products, in the development of CVD is incompletely understood. Although increased public awareness of the harms of cigarette smoking has successfully led to a decline in its prevalence, the use of electronic cigarettes (e-cig) or electronic nicotine delivery system has increased dramatically in recent years because of the perception that these products are safe. This review summarizes our current knowledge of the expression and function of the nicotinic acetylcholine receptors in the cardiovascular system and the impact of nicotine exposure on cardiovascular health, with a focus on nicotine-induced vascular dysfunction. Nicotine alters vasoreactivity through endothelium-dependent and/or endothelium-independent mechanisms, leading to clinical manifestations in both cigarette smokers and e-cig users. In addition, nicotine induces vascular remodelling through its effects on proliferation, migration and matrix production of both vascular endothelial and vascular smooth muscle cells. The purpose of this review is to identify critical knowledge gaps regarding the effects of nicotine on the vasculature and to stimulate continued nicotine research.

The outcome of bone graft surgery for nonunion of fractures of the scaphoid

Data on 806 patients undergoing bone graft surgery for a scaphoid fracture nonunion were retrospectively collected at 19 centres in the United Kingdom. Each centre contributed at least 30 cases. Sufficient data were available in 462 cases to study factors that influenced the outcome of surgery. Overall union occurred in at least 69%, and nonunion in at least 22%, with 9% of cases having 'uncertain union status'. Union appeared to be adversely influenced by smoking and the time between acute scaphoid fracture and nonunion surgery, with adjusted odds ratios of 1.8 and 2.4, respectively, but neither achieved the pre-determined significance level of 0.003. The type of bone graft (vascular vs non-vascular; iliac crest vs distal radius) did not appear to influence outcome. Further large multicentre prospective studies with clear definitions of 'union' and other factors are needed to clarify whether modification of surgical technique can influence union. Level of evidence: IV.

Deletion of nicotinic acetylcholine receptor alpha9 in mice resulted in altered bone structure

Alterations in bone strength and structure were found in knockout (KO) mouse strains with deletion of several acetylcholine receptors. Interestingly, the expression of the nicotinic acetylcholine receptors (nAChR) subunit α10 was down-regulated in osteogenic differentiated mesenchymal stem cells of patients with osteoporosis whereas the expression of subunit α9 was not altered. Since nAChR subunits α9 and α10 are often combined in a functional receptor, we analyzed here the bone of adult female KO mice with single deletion of either nAChR alpha9 (α9KO) or alpha10 (α10KO). Biomechanical testing showed a significant decrease of bending stiffness and maximal breaking force in α9KO compared to their corresponding wild type mice. Furthermore, an increase in trabecular pattern factor (Tb.Pf) and structure model index (SMI) was detected by μCT in α9KO indicating reduced bone mass. On the mRNA level a decrease of Collagen 1α1 and Connexin-43 was measured by real-time RT-PCR in α9KO while no alteration of osteoclast markers was detected in either mouse strain. Using electron microcopy we observed an increase in the number of osteocytes that showed signs of degeneration and cell death in the α9KO compared to their wild type mice, while α10KO showed no differences. In conclusion, we demonstrate alterations in bone strength, structure and bio-marker expression in α9KO mice which imply the induction of osteocyte degeneration. Thus, our data suggest that nAChR containing the α9 subunit might be involved in the homeostasis of osteocytes and therefore in bone mass regulation.

Safety and Efficacy of Nicotine Replacement Therapy in the Perioperative Period: A Narrative Review

Patients who smoke cigarettes are at increased risk for development of complications both during and after surgical procedures, including respiratory, cardiac, and healing-related complications. Abstinence from smoking can considerably reduce these risks. Pharmacotherapy, including nicotine replacement therapy (NRT), is an important component of efficacious tobacco use interventions. However, the use of NRT in the perioperative period is controversial. In this narrative review, we discuss the current evidence for the efficacy and safety of NRT in patients scheduled for surgical procedures, with emphasis on evidence from human studies. We performed a literature search for articles published from January 1, 1990, through May 1, 2015, in the PubMed online database using various permutations of the Medical Subject Headings terms surgery; surgical procedures, operative; nicotine; and smoking cessation. Studies were selected for inclusion according to their relevance to the preclinical and clinical evidence pertaining to how NRT affects surgical outcome and long-term rates of abstinence from tobacco. There is strong evidence that NRT enhances the efficacy of tobacco use interventions. Some preclinical studies suggest that nicotine in high doses that exceed those produced by NRT decreases the viability of skin flaps. Although the available data are limited, there is no evidence from human studies that NRT increases the risk of healing-related or cardiovascular complications. Individual clinical trials of tobacco use interventions that include NRT have revealed either no effect or a reduction in complication rates. Therefore, given the benefits of smoking abstinence to both perioperative outcomes and long-term health and the efficacy of NRT in achieving and maintaining abstinence, any policies that prohibit the use of NRT in surgical patients should be reexamined.

Effect of serum nicotine level on posterior spinal fusion in an in vivo rabbit model

BACKGROUND CONTEXT

Cigarette smoking has a deleterious effect on spinal fusion. Although some studies have implied that nicotine is primarily responsible for poor fusion outcomes, other studies suggest that nicotine may actually stimulate bone growth. Hence, there may be a dose-dependent effect of nicotine on posterior spinal fusion outcomes.

PURPOSE

The purpose of this study was to determine if such a relationship could be shown in an in vivo rabbit model.

STUDY DESIGN/SETTING

This is a prospective in vivo animal study.

METHODS

Twenty-four adult male New Zealand white rabbits were randomly divided into four groups. All groups received a single-level posterolateral, intertransverse process fusion at L5-L6 with autologous iliac crest bone. One group served as controls and only underwent the spine fusion surgery. Three groups received 5.25-, 10.5-, and 21-mg nicotine patches, respectively, for 5 weeks. Serum nicotine levels were recorded for each group. All animals were euthanized 5 weeks postoperatively, and spinal fusions were evaluated radiographically, by manual palpation, and biomechanically. Statistical analysis evaluated the dose response effect of outcomes variables and nicotine dosage. This study was supported by a portion of a $100,000 grant from the Orthopaedic Research and Education Foundation. Author financial disclosures were completed in accordance with the journal's guidelines; there were no conflicts of interests disclosed that would have led to bias in this work.

RESULTS

The average serum levels of nicotine from the different patches were 7.8±1.9 ng/mL for the 5.25-mg patch group; 99.7±17.7 ng/mL for the 10.5-mg patch group; and 149.1±24.6 ng/mL for the 21-mg patch group. The doses positively correlated with serum concentrations of nicotine (correlation coefficient=0.8410, p<.001). The 5.25-mg group provided the best fusion rate, trabeculation, and stiffness. On the basis of the palpation tests, the fusion rates were control (50%), 5.25 mg (80%), 10.5 mg (50%), and 21 mg (42.8%). Radiographic assessment of trabeculation and bone incorporation and biomechanical analysis of bending stiffness ratio were also greatest in the 5.25-mg group. Radiographic evaluation showed a significant (p=.0446) quadratic effect of nicotine dose on spinal fusion.

CONCLUSIONS

The effects of nicotine on spinal fusion are complex, may be dose dependent, and may not always be detrimental. The uniformly negative effects of smoking reported in patients undergoing spinal fusion may possibly be attributed to the other components of cigarette smoke.

Nicotine effect on bone remodeling during orthodontic tooth movement: histological study in rats

INTRODUCTION

Nicotine is harmful to angiogenesis, osteogenesis and synthesis of collagen.

OBJECTIVE

The aim of this study was to investigate the effect of nicotine on bone remodeling during orthodontic movement in rats.

METHODS

Eighty male Wistar rats were randomly divided into three groups: Group C (control), group CM (with orthodontic movement) and group NM (nicotine with orthodontic movement) groups. The animals comprising groups C and CM received 0.9% saline solution while group NM received nicotine solution (2 mg/kg). A nickel-titanium closed-coil spring was used to induce tooth movement. The animals were euthanized and tissue specimens were histologically processed. Blood vessels, Howship's lacunae and osteoclast-like cells present in the tension and compression areas of periodontal ligaments were quantified. The extent of bone formation was evaluated under polarized light, to determine the percentage of immature/mature collagen.

RESULTS

It was observed lower blood vessel densities in the NM group in comparison to the CM group, three (p < 0.001) and seven (p < 0.05) days after force application. Osteoclast-like cells and Howship's lacunae in the NM group presented lower levels of expression, in comparison to the CM group, with significant differences on day 7 (p < 0.05 for both variables) and day 14 (p < 0.05 for osteoclast-like cells and p < 0.01 for Howship's lacunae). The percentage of immature collagen was increased in the NM group in comparison to the CM group, with a statistically significant difference on day 3 (p < 0.05), day 7 (p < 0.001), day 14 (p < 0.001) and day 21 (p < 0.001).

CONCLUSIONS

Nicotine affects bone remodeling during orthodontic movement, reducing angiogenesis, osteoclast-like cells and Howship's lacunae, thereby delaying the collagen maturation process in new bone matrix.

The Effects of Smoking on the Osmotic Pressure of Human Dental Pulp Tissue

OBJECTIVE

We aimed to investigate the effect of smoking on the osmotic pressure (OP) of human dental pulp tissue.

MATERIALS AND METHODS

Sixty male dental patients (smokers and nonsmokers) scheduled for root canal treatment for prosthodontics were included in the study. Fifteen patients (1 premolar tooth/patient) were allocated to each of the following groups according to their smoking habits, i.e. group 1: ≤10 cigarettes/day, group 2: 11-20 cigarettes/day, group 3: >20 cigarettes/day and group 4: nonsmoking controls. Apical pulp tissues were removed via coronal access. Pulp tissue supernatants were obtained to measure the pulpal OP by means of a semimicro digital osmometer. One-way analysis of variance and the post hoc Duncan test were used to analyze the differences in OP between groups. Regression analysis was used to determine the relationship between the number of cigarettes smoked daily and the pulpal OP.

RESULTS

The mean (± SD) OP value decreased as cigarette consumption increased: group 4 (268.00 ± 10.09 mosm/kg) > group 1 (259.20 ± 7.16 mosm/kg) > group 2 (248.90 ± 2.23 mosm/kg) > group 3 (239.90 ± 7.40 mosm/kg). The OP differed significantly between groups (p < 0.01), and a significant negative correlation was found between cigarette consumption and pulpal OP (r = -0.809, p < 0.01).

CONCLUSION

In this study, the OP decreased as the number of cigarettes smoked increased. In clinical examination, there may be misdiagnosis of pulpal conditions in smokers (even in healthy pulp tissue) due to the effect of altered OP on pulpal tissue reactions.

Validated Laser Doppler protocol for measurement of mouse bone blood perfusion - response to age or ovariectomy differs with genetic background

The physiological role of bone vascularization in bone metabolism begins to be understood; however, its involvement in pathological situations remains poorly explored. Bone blood supply depends on both vascular density and blood flow. However, in mice, the specific evaluation of perfusion in bone suffers from a lack of easy-handling measurement tools. In the present study, we first developed a Laser Doppler Perfusion Measurement (LDPM) protocol in mouse tibia, which we validated with ex vivo and in vivo experiments. Then we carried out a study associating both structural (vascular quantitative histomorphometry) and functional (LDPM) approaches. We studied the effects of aging in 4, 7 and 17 month-old male mice and the early effects of ovariectomy in 4 month-old females. Both studies were carried out in inbred mice (C57BL/6) and in mice of mixed background (129sv/CD1). The significant differences we observed between strains in unchallenged 4 month-old animals concerned both perfusion and vascular density and depended on gender. Additionally, the age-related bone loss observed in male mice was not temporally associated with vascular changes in either strain. Between 7 and 17 months, we did not find any decrease in bone vascular density or perfusion. In contrast, ovariectomy triggered early vascular structural and functional adaptations which differed between genetic backgrounds. We observed that bone vessel density did not generally account for bone perfusion levels. In conclusion, we describe here a LDPM-based experimental protocol which provides a reproducible quantitative evaluation of bone perfusion in mouse tibia, hence allowing intergroup comparisons. This integrative structural and functional approach of bone vascularization showed that bone vascular adaptation occurs during aging or after ovariectomy and is affected by the genetic background.

Nicotine Increases Osteoblast Activity of Induced Bone Marrow Stromal Cells in a Dose-Dependent Manner: An in vitro Cell Culture Experiment

Previous studies by our group showed that nicotine delivered via a transdermal nicotine patch significantly enhanced posterior spinal fusion rates in rabbits. Nicotine transdermal patches provide a steady serum level; there may be a dose-dependent effect of nicotine on posterior spinal fusion. In an in vitro cell culture model of rabbit bone marrow-derived osteoblast-like cells, cells were exposed to different concentrations of nicotine (0, 20, 40, 80 ng/mL and 10, 100, 250 μg/mL). Wells were stained with an alkaline phosphatase (ALP) staining kit to determine ALP enzyme activity. Cells were stained with Von Kossa for mineralization. A two-way analysis of variance (ANOVA) using dose and time as variables showed significant differences among groups; post hoc analysis showed that the 100-μg/mL dose of nicotine significantly enhanced ALP activity over controls. A one-way ANOVA using dose as the variable showed that the 100- and 250-μg/mL doses had significantly greater mineralization than controls. Dose-response analysis revealed a statistically significant effect of nicotine dose on ALP activity and Von Kossa activity. The effects of nicotine on spinal fusion may be dose-dependent and due to stimulation of osteoblastic activity. Nicotine may not be responsible for the inhibited bone healing observed in smokers.

Exercise training restores impaired dilator responses of cerebral arterioles during chronic exposure to nicotine

Our goal was to determine whether exercise training (ExT) alleviates impaired nitric oxide synthase (NOS)-dependent dilation of pial arterioles during chronic exposure to nicotine. We measured dilation of cerebral (pial) arterioles in sedentary and exercised control and nicotine-treated (2 mg·kg(-1)·day(-1) for 4 wk via an osmotic minipump) rats to an endothelial NOS (eNOS)-dependent (ADP), a neuronal NOS (nNOS)-dependent [N-methyl-D-aspartic acid (NMDA)], and a NOS-independent (nitroglycerin) agonist. In addition, we harvested brain tissue from sedentary and exercised control and nicotine-treated rats to measure the production of superoxide anion and measured superoxide dismutase-1 (SOD-1) protein in cerebral microvessels using Western blot. We found that eNOS-and nNOS-dependent, but not NOS-independent, vasodilation was impaired in nicotine-treated compared with control rats. In addition, the production of superoxide anion (lucigenin chemiluminescence) was increased, and SOD-1 protein decreased, in rats treated with nicotine compared with control rats. Further, although ExT did not significantly affect eNOS- or nNOS-dependent vasodilation in control rats, ExT restored impaired eNOS- and nNOS-dependent responses in nicotine-treated rats. In addition, the increase in superoxide anion production observed in nicotine-treated rats was reduced by ExT, and SOD-1 protein was increased in nicotine-treated rats by ExT. We suggest that ExT restores impaired NOS-dependent dilation of pial arterioles during chronic exposure to nicotine by a mechanism related to the formation of superoxide anion.

Uncoupled angiogenesis and osteogenesis in nicotine-compromised bone healing

Nicotine is the main chemical component responsible for tobacco addiction. This study aimed to evaluate the influence of nicotine on angiogenesis and osteogenesis and the associated expression of angiogenic and osteogenic mediators during bone healing. Forty-eight adult New Zealand White rabbits were randomly assigned to a nicotine group and a control group. Nicotine pellets (1.5 g, 60-day time release) or placebo pellets were implanted in the neck subcutaneous tissue. The nicotine or placebo exposure time for all the animals was 7 weeks. Unilateral mandibular distraction osteogenesis was performed. Eight animals in each group were euthanized on day 5, day 11 of active distraction, and week 1 of consolidation, respectively. The mandibular samples were subjected to radiographic, histologic, immunohistochemical, and real-time reverse-transcriptase polymerase chain reaction examinations. Nicotine exposure upregulated the expression of hypoxia inducible factor 1alpha and vascular endothelial growth factor and enhanced angiogenesis but inhibited the expression of bone morphogenetic protein 2 and impaired bone healing. The results indicate that nicotine decouples angiogenesis and osteogenesis in this rabbit model of distraction osteogenesis, and the enhanced angiogenesis cannot compensate for the adverse effects of nicotine on bone healing.

Expression of non-neuronal cholinergic system in osteoblast-like cells and its involvement in osteogenesis

Acetylcholine (ACh) is detected in a variety of non-neuronal cells where it acts as a para/autocrine signaling molecule controlling basic cell functions such as proliferation, differentation, and maintenance of cell-cell contacts. ACh-synthesizing enzymes include choline acetyltransferase and carnitine acetyltransferase (CarAT). ACh is released through vesicular exocytosis or directly from the cytoplasm via organic cation transporters (OCT). Extracellular ACh binds to nicotinic (nAChR) and muscarinic receptors (MR). Degradation of ACh is performed by acetylcholinesterase and butyrylcholinesterase (BChE). Here, we have determined whether these molecules are expressed in osteoblast-like cells, by means of reverse transcription polymerase chain reaction and immunohistochemistry, focusing on nAChR subunits alpha3 and alpha5. RNA for CarAT, OCT-1, M2R, M5R, nAChR subunits alpha3, alpha5, alpha9, alpha10, beta2, beta3, and BChE were detected in human (SAOS-2) and murine (MC3T3-E1) osteoblast-like cells. Other cholinergic components were only expressed species-specifically, e.g., M3R and nAChR subunit alpha7. Immunhistochemistry localized the nAChR subunits alpha3 and alpha5 in osteoblasts in vitro and in vivo where they were up-regulated after application of bone morphogenetic protein-2 (BMP-2) during fracture healing in a rat model. Thus, the cholinergic system of osteoblast-like cells might be regulated by BMP-2 during bone remodeling. Osteoblast-like cells express all necessary enzymes, transporters, and receptors for ACh synthesis and recycling.

Role of non-neuronal nicotinic acetylcholine receptors in angiogenesis

Angiogenesis is a critical physiological process for cell survival and development. Endothelial cells, necessary for the course of angiogenesis, express several non-neuronal nicotinic acetylcholine receptors (AChRs). The most important functional non-neuronal AChRs are homomeric alpha7 AChRs and several heteromeric AChRs formed by a combination of alpha3, alpha5, beta2, and beta4 subunits, including alpha3beta4-containing AChRs. In endothelial cells, alpha7 AChR stimulation indirectly triggers the activation of the integrin alphavbeta3 receptor and an intracellular MAP kinase (ERK) pathway that mediates angiogenesis. Non-selective cholinergic agonists such as nicotine have been shown to induce angiogenesis, enhancing tumor progression. Moreover, alpha7 AChR selective antagonists such as alpha-bungarotoxin and methyllycaconitine as well as the non-specific antagonist mecamylamine have been shown to inhibit endothelial cell proliferation and ultimately blood vessel formation. Exploitation of such pharmacologic properties can lead to the discovery of new specific cholinergic antagonists as anti-cancer therapies. Conversely, the pro-angiogenic effect elicited by specific agonists can be used to treat diseases that respond to revascularization such as diabetic ischemia and atherosclerosis, as well as to accelerate wound healing. In this mini-review we discuss the pharmacological evidence supporting the importance of non-neuronal AChRs in angiogenesis. We also explore potential intracellular mechanisms by which alpha7 AChR activation mediates this vital cellular process.

Effect of systemic administration of nicotine on healing in osseous defects. An experimental study in rabbits. Part II

OBJECTIVES

The aim of the present study was to analyze the effect of systemic administration of nicotine on bone healing in osseous defects in the tibia of rabbits.

MATERIAL AND METHODS

Sixteen female rabbits received nicotine (n=8; test group) or saline (n=8; control group) via subcutaneously placed mini-osmotic pumps for 8 weeks. The animals underwent three surgical operations during the experimental period, and body weight was registered weekly. Blood samples were collected to determine cotinine and prostaglandin E(2) levels. Bone preparations were made in the right leg of all rabbits after 4 weeks and in the left leg after 6 weeks of nicotine/placebo exposure. Thus, 2- and 4-week healing groups were created for the bone defects. After 8 weeks, the animals were killed. Tissue blocks including the bone defects were prepared for histological analysis.

RESULTS

The animals in the test group lost weight, while the control group gained weight during the experiment. The prostaglandin E(2) levels in plasma increased significantly following nicotine exposure in the test group. No significant differences in the percentage of vessels and bone density in the osseous defects were found between the test and the control groups after 2 and 4 weeks of healing.

CONCLUSIONS

In this experiment, systemic administration of nicotine over 4 or 6 weeks, respectively, influenced body weight and systemic prostaglandin E(2) levels but not the amount of blood vessels and the bone mineral density in bone defects after 2 or 4 weeks of healing.

Blood volume and haemoglobin oxygen content changes in human bone marrow during orthostatic stress

The interest in, and the need for effective measures to be used in screening, diagnosis, and the follow-up of skeletal pathologies is growing markedly. This paper proposes a completely new and non-invasive technique allowing the study of the human tibia bone marrow (BM) haemodynamics with a time resolution of 1 s. The technique, based on near infrared spectroscopy, is sensitive enough to allow the detection of BM blood volume and/or oxygen saturation changes during orthostatic variations imposed by a tilt bed. An increase in the slope of the bed of 15 degrees is sufficient to detect this phenomenon. The ability to study the possible presence of a neural control of BM haemodynamics is also discussed. No other existing technique currently allows one to obtain the proposed results and this approach might open up a new field of study related to human BM physiology.

The influence of cigarette smoke inhalation and its cessation on the tooth-supporting alveolar bone: a histometric study in rats

OBJECTIVE

It has been previously shown that smoking may enhance periodontal breakdown and impair bone healing around titanium implants. However, there is a lack of information concerning the effect of smoking on the tooth-supporting alveolar bone. Thus, the aim of this study was to histometrically evaluate the influence of cigarette smoke inhalation and its cessation on tooth-supporting alveolar bone.

METHODS

Sixty male Wistar rats were randomly assigned to one of the following groups: group 1 - control (n = 15), group 2 - 2 months of cigarette smoke inhalation (n = 13), group 3 - 3 months of cigarette smoke inhalation and 2 months without exposure to cigarette smoke inhalation (n = 16) and group 4 - 5 months of cigarette smoke inhalation (n = 16). Five months after the beginning of cigarette smoke inhalation regime (2 months for group 2), the animals were killed and the mandible was removed and prepared for histological sections. The proportion of mineralized tissue in the furcation area (i.e. a 1000 microm zone under the furcation and between the roots) was obtained.

RESULTS

Data analysis demonstrated that the animals continuously exposed to cigarette smoke inhalation presented a decreased proportion of mineralized tissue (groups 2 and 4), when compared to control and cessation groups (groups 1 and 3) (p < 0.05). Similar levels of proportion of mineralized tissue were observed in groups 1 and 3, showing a beneficial effect of cigarette smoke inhalation cessation on proportion of mineralized tissue.

CONCLUSION

Within the limits of the present study, it can be concluded that cigarette smoke inhalation may affect the tooth-supporting bone as early as 2 months after the initial exposure, and that smoke exposure cessation may revert its negative impact on the alveolar bone.

Bony palatal necrosis in a diabetic patient secondary to palatal rotational flap

Donor site necrosis is a very rare complication of palatal rotational flaps. The aim of this case report is to present a 43-year-old female, Type I diabetic patient with a chronic oroantral fistula in the right second molar region. The patient had bony necrosis in the donor site following palatal rotational flap operation. The treatment approach and the alternative methods are discussed.

Inhibition of NADPH oxidase improves impaired reactivity of pial arterioles during chronic exposure to nicotine

Our goals were to determine whether chronic exposure to nicotine alters nitric oxide synthase (NOS)-dependent reactivity of cerebral (pial) arterioles and to identify a potential role for NADPH oxidase in impaired NOS-dependent responses during chronic exposure to nicotine. We measured in vivo diameter of pial arterioles to NOS-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in saline-treated rats and rats chronically treated with nicotine (2 mg.kg(-1).day(-1) for 2 wk via an osmotic minipump). We found that NOS-dependent, but not -independent, vasodilatation was impaired in nicotine-treated compared with saline-treated rats. In addition, the production of superoxide anion (lucigenin chemiluminescence) was increased in rats treated with nicotine compared with saline-treated rats. Furthermore, using Western blot analysis, we found that chronic exposure to nicotine increased p47phox protein in the parietal cortex. Finally, we found that apocynin (40 mg.kg(-1).day(-1)) in the drinking water to inhibit NADPH oxidase alleviated impaired NOS-dependent cerebral vasodilatation in nicotine treated rats but did not alter NOS-dependent responses in saline treated rats and did not alter NOS-independent reactivity in saline- or nicotine-treated rats. These findings suggest that chronic exposure to nicotine impairs NOS-dependent dilatation of pial arterioles by a mechanism that appears to be related to the formation of superoxide anion via activation of NADPH oxidase.