Inspiratory muscle warm-up does not improve cycling time-trial performance.

PURPOSE: This study examined the effects of an active cycling warm-up, with and without the addition of an inspiratory muscle warm-up (IMW), on 10-km cycling time-trial performance. METHODS: Ten cyclists (VO2 = 65 ± 9 mL kg(-1) min(-1)) performed a habituation 10-km cycling time-trial and three further time-trials preceded by either no warm-up (CONT), a cycling-specific warm-up (CYC) comprising three consecutive 5-min bouts at powers corresponding to 70, 80, and 90% of the gas exchange threshold, or a cycling-specific warm-up preceded by an IMW (CYC + IMW) comprising two sets of 30 inspiratory efforts against a pressure-threshold load of 40% maximal inspiratory pressure (MIP). The cycling warm-up was followed by 2-min rest before the start of the time-trial. RESULTS: Time-trial performance times during CYC (14.75 ± 0.79 min) and CYC + IMW (14.70 ± 0.75 min) were not different, although both were faster than CONT (14.99 ± 0.90 min) (P < 0.05). Throughout the time-trial, physiological (minute ventilation, breathing pattern, pulmonary gas exchange, heart rate, blood lactate concentration and pH) and perceptual (limb discomfort and dyspnoea) responses were not different between CYC and CYC + IMW. Baseline MIP during CONT and CYC was 151 ± 31 and 156 ± 39 cmH2O, respectively, and was unchanged following the time-trial. MIP increased by 8% after IMW (152 ± 27 vs. 164 ± 27 cmH2O, P < 0.05) and returned to baseline after the time-trial. CONCLUSIONS: Improvements in 10-km cycling time-trial performance following an active cycling warm-up were not magnified by the addition of an IMW. Therefore, an appropriately designed active whole-body warm-up does adequately prepare the inspiratory muscles for cycling time-trials lasting approximately 15 min.

Effects of 24-week prebiotic intervention on self-reported upper respiratory symptoms, gastrointestinal symptoms, and markers of immunity in elite rugby union players.

OBJECTIVES: Elite rugby union players face numerous physiological and psychological stressors which can increase upper respiratory and gastrointestinal illness risk, and in turn can compromise training and competitive performance. This study aimed to investigate the effect of daily prebiotic supplementation on upper respiratory symptoms, gastrointestinal symptoms, and markers of immune function in elite rugby union players. METHODS: Thirty-three elite rugby union players were randomly assigned to consume a prebiotic (2.8 g/day galactooligosaccharide) or placebo (2.8 g/day maltodextrin), daily for 168 days under double-blind conditions. Participants completed daily and weekly questionnaires for self-reported upper respiratory and gastrointestinal symptoms respectively. Blood and saliva samples were collected at 0, 84, and 168 days for assessment of plasma TNF-α and CRP, and saliva IgA respectively. RESULTS: The prebiotic group experienced a 2-day reduction in upper respiratory symptom duration (P = 0.045). Gastrointestinal symptom severity and incidence were lower in the prebiotic group compared to the placebo group (P < 0.001, P = 0.041) respectively. Salivary immunoglobulin A secretion rate was 42% greater in the prebiotic group compared to the placebo group at day 168 (P = 0.004), no differences in CRP and TNF-α were found (P > 0.05). CONCLUSION: A 168-day dietary prebiotic intervention reduced the duration of upper respiratory symptoms and reduced the incidence and severity of gastrointestinal symptoms in elite rugby union players. These findings suggest that seasonal prebiotic interventions may be beneficial for reducing illness in elite rugby union players, improving their availability to train and compete.Key pointsElite athletes are susceptible to upper respiratory symptoms and gastrointestinal symptoms which may impact upon training availability and competition performance.For the first time, this study shows that a dietary prebiotic intervention can reduce the duration of upper respiratory symptoms by 2 days in elite rugby union players.Dietary prebiotic supplementation can improve the incidence and severity of gastrointestinal symptoms experienced by elite rugby union players.Prebiotic supplementation was able to increase salivary IgA secretion after 168 days.These findings can inform practice suggesting that seasonal prebiotic use has the potential to modulate immune function and reduce illness in elite rugby union, which may improve a player's availability to train and compete.The mechanisms by which prebiotics reduce URS and GIS require further research exploration.

The effect of trait self-control on dyspnoea and tolerance to a CO2 rebreathing challenge in healthy males and females.

BACKGROUND: High trait self-control is associated with greater tolerance of unpleasant sensations including effort and pain. Dyspnoea and pain have several commonalities and this study aimed to investigate for the first time whether trait self-control influences responses to a hypercapnic rebreathing challenge designed to induce dyspnoea. As sex also influences tolerance to dyspnoea, we also sought to investigate whether this moderated the role of trait self-control. METHODS: Participants (n = 65, 32 females) scoring high or low for trait self-control, performed a standardised rebreathing challenge, in which inspired carbon dioxide (CO2) gradually increased over a period of 6 min or until an intolerable level of dyspnoea. Air hunger (AH) intensity - a distinctive quality of dyspnoea, was measured every 30 s. The multidimensional dyspnoea profile (MDP) was completed after the rebreathing challenge for a more complete overview of breathing discomfort. RESULTS: Males high in trait self-control (SCHIGH) (302 ± 42 s), tolerated the rebreathing challenge for longer than males low in self-control (SCLOW) (252 ± 66 s, P = 0.021), experienced slower increases in AH intensity during the rebreathing challenge (0.03 ± 0.01 cm.s - 1 vs. 0.04 ± 0.01 cm.s - 1,P = 0.045) and reported lower perceived mental effort on the MDP (4.94 ± 2.46 vs. 7.06 ± 1.60, P = 0.007). There was no difference between SCHIGH and SCLOW females for challenge duration. However, SCHIGH females (9.29 ± 0.66 cm) reported greater air hunger at the end of the challenge than SCLOW females (7.75 ± 1.75 cm, P = 0.003). It is possible that SCLOW females were unwilling to tolerate the same perceptual intensity of AH as the SCHIGH females. CONCLUSIONS: These results indicate that individuals high in trait self-control are more tolerant of dyspnoea during a CO2 rebreathing challenge than low self-control individuals. Tolerance of the stimulus was moderated by the sex of the participant, presenting an interesting opportunity for future research.

Effects of protocol design on lactate minimum power.

The aim of this investigation was to use a validated lactate minimum test protocol and evaluate whether blood lactate responses and the lactate minimum power are influenced by the starting power (study 1) and 1 min inter-stage rest intervals (study 2) during the incremental phase. Study 1: 8 subjects performed a lactate minimum test comprising a lactate elevation phase, recovery phase, and incremental phase comprising 5 continuous 4 min stages with starting power being 40% or 45% of the maximum power achieved during the lactate elevation phase, and with power increments of 5% maximum power. Study 2: 8 subjects performed 2 identical lactate minimum tests except that during one of the tests the incremental phase included 1 min inter-stage rest intervals. The lactate minimum power was lower when the incremental phase commenced at 40% (175±29 W) compared to 45% (184±30 W) maximum power (p<0.01), and was increased when 1 min inter-stage rest intervals were included during the incremental phase (192±25 vs. 200±26 W, p<0.01). In conclusion, changes in lactate minimum power were small and thus unlikely to compromise test validity and therefore training status evaluation and exercise prescription.

Investigations of the lactate minimum test.

We evaluated: the agreement between lactate minimum and maximal lactate steady state (MLSS) cycling powers (study 1); whether rates of change of blood lactate concentration during the lactate minimum test reflect that of constant power exercise (study 2); whether the lactate minimum power is influenced by the muscle groups used to elevate blood lactate concentration (study 3). Study 1: 32 subjects performed a lactate minimum test comprising a lactate elevation phase, recovery phase, and incremental phase (five 4 min stages); MLSS was subsequently determined. Study 2: 8 subjects performed a lactate minimum test and five 22 min constant power tests at the incremental phase exercise intensities. Study 3: 10 subjects performed two identical lactate minimum tests, except during the second test the lactate elevation phase comprised arm-cranking. Lactate minimum and MLSS powers demonstrated good agreement (mean bias+/-95% limits of agreement: 2+/-22 W). Rates of change of blood lactate concentration during each incremental phase stage and corresponding constant power test did not correlate. Lactate minimum power was lowered when arm-cranking was used during the lactate elevation phase (157+/-29 vs. 168+/-21 W; p<0.05). The lactate elevation phase modifies blood lactate concentration responses during the incremental phase, thus good agreement between lactate minimum and MLSS powers seems fortuitous.

A 4-year follow-up study of atopic dermatitis therapy with 0.1% tacrolimus ointment in children and adult patients.

BACKGROUND: For the treatment of a chronic disease like atopic dermatitis, sustained tolerability and efficacy of the applied medication are essential. OBJECTIVES: The present open-label, noncomparative study was conducted to obtain information on the long-term safety and efficacy of 0.1% tacrolimus ointment. METHODS: Patients aged 2 years or older with an affected body surface area of more than 5%, who previously participated in a clinical trial on tacrolimus ointment, were eligible for this study. The treatment area was defined by the investigator at study entry. Both children and adults applied continuously or intermittently 0.1% tacrolimus ointment twice daily during episodes of active disease plus an additional week after remission over a follow-up period of up to 4 years. RESULTS: The intent-to-treat population comprised 782 patients, with a median age of 22 years (range 2-72). Patients remained in the study for up to 4 years. Approximately half of the patients discontinued the study prematurely; the median follow-up was 1422 days. Median tacrolimus ointment use was 31.2 g during the first week; ointment use decreased during the first year and then remained stable for the remainder of the study. The median cumulative tacrolimus use was 271.5 g at month 6, 462.5 g at month 12, 739.9 g at month 24, 1029.3 g at month 36 and 1320.8 g at month 48. Altogether 51.8% of patients discontinued the study prematurely; the main reasons were withdrawal of consent (13.3%), loss to follow-up (11.3%) and lack of efficacy (9.4%). Adverse events led to study discontinuation in 3.7% of the patients. The most frequent application site events were skin burning and pruritus. These events were most often reported in adult patients during the initial treatment period; prevalence decreased after the first week and remained at a low level throughout the study. Nonapplication site events occurred with stable incidences throughout the study period. In general, calculated daily hazard rates did not indicate an increased risk of adverse events with prolonged treatment. The total affected body surface area decreased substantially upon onset of treatment and efficacy of treatment was maintained until the end of the study with smaller but continuous improvements throughout the follow-up period. Overall, 75% of the patients and 76% of the investigators rated their satisfaction with the treatment as excellent, very good or good at the end of the study or at the time of premature discontinuation. CONCLUSIONS: The safety profile of intermittent or continuous long-term application of 0.1% tacrolimus ointment for up to 4 years was consistent with that which has been established from shorter studies and gave no reason for concern. In addition, 0.1% tacrolimus ointment demonstrated sustained efficacy as reflected by the expression of high satisfaction with treatment by both patients and investigators.

Locomotor muscle fatigue is not critically regulated after prior upper body exercise.

This study examined the effects of prior upper body exercise on subsequent high-intensity cycling exercise tolerance and associated changes in neuromuscular function and perceptual responses. Eight men performed three fixed work-rate (85% peak power) cycling tests: 1) to the limit of tolerance (CYC); 2) to the limit of tolerance after prior high-intensity arm-cranking exercise (ARM-CYC); and 3) without prior exercise and for an equal duration as ARM-CYC (ISOTIME). Peripheral fatigue was assessed via changes in potentiated quadriceps twitch force during supramaximal electrical femoral nerve stimulation. Voluntary activation was assessed using twitch interpolation during maximal voluntary contractions. Cycling time during ARM-CYC and ISOTIME (4.33 ± 1.10 min) was 38% shorter than during CYC (7.46 ± 2.79 min) (P < 0.001). Twitch force decreased more after CYC (-38 ± 13%) than ARM-CYC (-26 ± 10%) (P = 0.004) and ISOTIME (-24 ± 10%) (P = 0.003). Voluntary activation was 94 ± 5% at rest and decreased after CYC (89 ± 9%, P = 0.012) and ARM-CYC (91 ± 8%, P = 0.047). Rating of perceived exertion for limb discomfort increased more quickly during cycling in ARM-CYC [1.83 ± 0.46 arbitrary units (AU)/min] than CYC (1.10 ± 0.38 AU/min, P = 0.003) and ISOTIME (1.05 ± 0.43 AU/min, P = 0.002), and this was correlated with the reduced cycling time in ARM-CYC (r = -0.72, P = 0.045). In conclusion, cycling exercise tolerance after prior upper body exercise is potentially mediated by central fatigue and intolerable levels of sensory perception rather than a critical peripheral fatigue limit.

Reproducibility of the bronchoconstrictive response to eucapnic voluntary hyperpnoea.

BACKGROUND: Eucapnic voluntary hyperpnoea (EVH) is considered an effective bronchoprovocation challenge for identifying exercise-induced bronchoconstriction (EIB). However, the reproducibility of the hyperpnoea-induced bronchoconstriction (HIB) response elicited by EVH remains unknown and was therefore the focus of this study. METHODS: Two cohorts of 16 physically active males (each cohort comprised 8 controls and 8 with physician diagnosis of asthma) participated in two studies of the short- and long-term reproducibility of the bronchoconstrictive response to an EVH test with dry air. EVH was performed on days 0, 7, 14, and 21 (short-term study), and 0, 35, and 70 (long-term study). HIB was diagnosed by a ≥10% fall in forced expiratory volume in 1 s (FEV1) after EVH. RESULTS: On day 0 of the short-term study, FEV1 fell by 2 ± 1% (P < 0.05) and 27 ± 18% (P < 0.01) from pre-to post-EVH in control and HIB-positive groups respectively. The post-EVH fall in FEV1 did not differ across the short-term study test days. In the HIB-positive group, the day-to-day coefficient of variation, reproducibility, and smallest meaningful change for the fall in FEV1 were 12%, 328 mL, and 164 mL, respectively. On day 0 of the long-term study, FEV1 fell by 2 ± 2% and 25 ± 18% (P < 0.01) after EVH in control and HIB-positive groups respectively. The post-EVH fall in FEV1 did not differ across the long-term study test days. In the HIB-positive group, the day-to-day coefficient of variation, reproducibility, and smallest meaningful change for the fall in FEV1 were 10%, 196 mL, and 98 mL respectively. CONCLUSION: The EVH test elicits a reproducible bronchoconstrictive response in physically active males with physician diagnosed asthma. These data thus support the clinical utility of the EVH test for EIB screening and monitoring.

A new keratin 2e mutation in ichthyosis bullosa of Siemens.

Ichthyosis bullosa of Siemens (IBS) is a rare autosomal dominant skin condition with features similar to epidermolytic hyperkeratosis (EH). Clinical symptoms are characterized by mild hyperkeratosis with an acral distribution. Histology shows epidermolysis of upper spinous and granular cells, whereas ultrastructurally, tonofilaments form perinuclear aggregates. IBS has been linked to the type II keratin cluster on chromosome 12q, and K2e mutations have recently been identified in IBS patients. We have studied genomic DNA from two IBS families and in both cases heterozygous point mutations were found in the 2B helical domain of K2e. One family had an established mutation in codon 493 (E493K), whereas the other had an unreported mutation in the adjacent codon (E494K). Both mutations were confirmed by allele-specific PCR. These data reinforce the hypothesis that mutations in the TYRKLLEGEE motif of the 2B helix are deleterious to keratin filament network integrity and provide further evidence for the involvement of K2e mutations in IBS.

Broad host range cloning vectors for gram-negative bacteria.

A series of cloning vectors has been constructed based on the broad-host-range plasmid R300B. One of these vectors, pGSS33, has a size of 13.4 kb and carries four antibiotic resistance genes [ampicillin (Apr), chloramphenicol (Cmr), streptomycin (Smr) and tetracycline (Tcr)], all of which have restriction sites for insertional inactivation. The derivation, structure and uses of the plasmids are described.

An increase in intracellular free calcium is an early event during differentiation of cultured human keratinocytes.

The effect of [Ca2+]o on [Ca2+]i in cultured human keratinocytes was studied using dual-wavelength microspectrofluorometric techniques. The results show that increasing [Ca2+]o from 70 microM to 1 mM causes an early rise in [Ca2+]i complete by 2 h. Heterogeneity within cultures was demonstrated. The [Ca2+]i in spontaneously differentiated cells of low Ca2+ cultures was similar to that of Ca2+ induced differentiated cells. The increase in [Ca2+]i preceded the morphological changes and growth inhibition induced by increasing [Ca2+]o. These observations are consistent with an increase in [Ca2+]i mediating differentiation of human keratinocytes.

Increased frequency of both total and specific monoclonal antibody producing hybridomas using a fusion partner that constitutively expresses recombinant IL-6.

The addition of auxiliary feeder cells or conditioned medium has been shown to augment the yield of mouse hybridomas obtained following the cell-cell fusion of myeloma and B lymphocytes. The addition of one of these factors, interleukin-6 (IL-6) has been found to increase the proportion of hybridomas secreting monoclonal antibodies of desired specificity. As an alternative genetic approach, we have examined the efficacy of a retroviral infectant of Sp2/0 cells that constitutively expresses recombinant murine IL-6 (Sp2/mIL-6) as fusion partner. The results demonstrated that the yields of both viable Ig-secreting hybridomas, and antigen-specific monoclonal antibodies were increased 3-15-fold and 5-9-fold, respectively, with the Sp2/mIL-6 relative to Sp2/0 or Sp2/neo cells as fusion partner. Sp2/mIL-6 cells generated hybridomas with comparable growth rates, stability, and Ig production. The results of staining nascent hybridoma colonies immunohistochemically for Ig production suggest that Sp2/mIL-6 cells as a fusion partner increased the viability and/or stability of nascent hybrid cells that are producing Ig. Thus the Sp2/mIL-6 cells are an improved myeloma parent for the generation of large numbers of antibody-producing hybridomas against specific antigens.

Survival of very young children with medulloblastoma (primitive neuroectodermal tumor of the posterior fossa) treated with craniospinal irradiation.

PURPOSE: Very young children with medulloblastoma are considered to have a worse prognosis than older children. As radiotherapy remains an important part of the treatment, the adverse prognosis could be due to inadequate radiation treatment rather than biological factors. We analyzed the published literature to examine the impact of radiotherapy on survival in this group. METHODS AND MATERIALS: A Medline search was performed and we reviewed studies of treatment of medulloblastoma where radiotherapy was delivered using megavoltage equipment and the minimum follow-up allowed the calculation of 5-year survival rates. RESULTS: Thirty-nine studies were published between 1979 and 1996 with a treatment including craniospinal irradiation and boost to the posterior fossa. Eleven studies comprising 1366 patients analyzed survival by age at diagnosis. Eight of 11 studies showed a worse 5-year survival for the younger patient group which reached statistical significance in two. There is also a suggestion of a higher proportion of children with metastatic disease at presentation in the very young age group. The usual policy in younger children was to give a lower dose of radiotherapy to the craniospinal axis (CSA) and posterior fossa (PF) with reduction of dose in the range of 15 to 25% compared to standard treatment. As dose reduction to the posterior fossa is associated with worse survival and local recurrence is the predominant site of failure, the major determinant of worse survival in very young children with medulloblastoma may be suboptimal radiotherapy. Protocols including postoperative chemotherapy with delayed, omitted, or only local tumor irradiation do not reach survival rates of protocols with standard radiotherapy, also suggesting a continued importance for irradiation. CONCLUSION: Very young children with medulloblastoma have a worse prognosis than older children. Inadequate radiation dose and technique to the primary tumor region may be a major contributing factor. Current chemotherapeutic regimes alone are not sufficient to compensate for reduced radiation doses and volumes.

Modifying radical radiotherapy in high grade gliomas; shortening the treatment time through acceleration.

PURPOSE: To evaluate the efficacy and toxicity of accelerated radiotherapy in patients with primary high grade glioma, where acceleration is used as a means of delivering a shortened course of radical radiotherapy. PATIENTS AND METHODS: Two-hundred and eleven patients with primary high grade glioma were treated at the Royal Marsden NHS Trust between 1987 and 1997 with accelerated radiotherapy (55 Gy in 34 fractions twice daily), to planning target volume (PTV) defined as enhancing tumour and a 3 cm margin. All had histologically confirmed high grade glioma (53 anaplastic astrocytoma, 137 glioblastoma multiforme, 4 gliosarcoma, 5 gemistocytic astrocytoma, 12 high grade astrocytoma not otherwise specified). The mean Karnofsky performance status (KPS) was 90 and median age was 54 years (range 19-77). RESULTS: Of 211 patients entered, 201 were able to complete radiotherapy; 39 patients (19%) had deterioration in KPS during radiotherapy and this was transient in 11. Median survival of 211 patients was 10 months with 1 year, 2 year, and 3 year survival probabilities of 38%, 14%, and 8% respectively. Age and extent of excision were independent prognostic factors for survival. Previous comparison to matched cohort receiving 60 Gy in 30 daily fractions did not demonstrate significant survival difference. CONCLUSION: Accelerated radiotherapy is a feasible treatment approach for patients with high grade glioma. The survival and functional outcome are comparable to conventional radiotherapy and the treatment is without serious acute toxicity. While acceleration of conventional dose irradiation could be tested in randomised studies, it is unlikely this approach would result in a clinically meaningful survival benefit. Accelerated radiotherapy therefore remains one of the ways of delivering radical irradiation in patients with high grade glioma. However, it adds complexity to what is a palliative treatment regimen and the rationale and advisability should be re-examined, particularly in terms of impact on quality of life, true patient preference, and health economic considerations.

Regulation of epidermal homeostasis through P2Y2 receptors.

1. Previous studies have indicated a role for extracellular ATP in the regulation of epidermal homeostasis. Here we have investigated the expression of P2Y2 receptors by human keratinocytes, the cells which comprise the epidermis. 2. Reverse transcriptase-polymerase chain reaction (RT - PCR) revealed expression of mRNA for the G-protein-coupled, P2Y2 receptor in primary cultured human keratinocytes. 3. In situ hybridization studies of skin sections revealed that P2Y2 receptor transcripts were expressed in the native tissue. These studies demonstrated a striking pattern of localization of P2Y2 receptor transcripts to the basal layer of the epidermis, the site of cell proliferation. 4. Increases in intracellular free Ca2+ concentration ([Ca2+]i) in keratinocytes stimulated with ATP or UTP demonstrated the presence of functional P2Y receptors. 5. In proliferation studies based on the incorporation of bromodeoxyuridine (BrdU), ATP, UTP and ATPgammaS were found to stimulate the proliferation of keratinocytes. 6. Using a real-time firefly luciferase and luciferin assay we have shown that under static conditions cultured human keratinocytes release ATP. 7. These findings indicate that P2Y2 receptors play a major role in epidermal homeostasis, and may provide novel targets for therapy of proliferative disorders of the epidermis, including psoriasis.

Intracellular calcium modulates the responses of human melanocytes to melanogenic stimuli.

Ultraviolet radiation (UVR), the synthetic diacyglycerol (DAG), 1-oleoyl-2-acetylglycerol (OAG), and cyclic AMP (cAMP) stimulants, including cholera toxin (CT) have all been shown to increase melanogenesis in cultured human melanocytes. Indirect evidence suggests that an increase in intracellular free Ca2+ ([Ca2+]i) may be important in stimulated melanogenesis. Therefore, to determine whether melanogenic responses are modulated by [Ca2+]i, the Ca2+ in the culture medium of melanocytes ([Ca2+]o) was raised from 70 microM to 1 mM. This switch in [Ca2+]o was associated with a biphasic increase in [Ca2+]i, with an early transient rise, over minutes, and a delayed sustained rise in [Ca2+]i, over hours. The early increase was blocked by nickel chloride (NiCl2), but not affected by depletion of [Ca2+]i stores by thapsigargin, suggesting that this [Ca2+]i rise was due to Ca2+ entry across the plasma membrane. Melanocytes cultured in the absence of CT had a reduced basal melanin content following the switch to 1 mM [Ca2+]o, but in the presence of CT, which acts by stimulating cAMP synthesis, the basal level was increased. Raising [Ca2+]o resulted in enhanced melanogenic responses to UVR and OAG, in the presence or absence of CT, suggesting that Ca(2+)-dependent mechanisms are important. UVR also stimulated a delayed rise in [Ca2+]i, over 24 h, but OAG did not. These results indicate that while [Ca2+]i is not essential for melanogenesis, it plays an important role in modulating the responses of melanocytes to melanogenic stimuli.

Superoxide dismutase restores endothelium-dependent arteriolar dilatation during acute infusion of nicotine.

We previously showed [Am. J. Physiol. 272 (Heart Circ. Physiol. 41): H2337-H2342, 1997] that nicotine impairs endothelium-dependent arteriolar dilatation. However, mechanisms that accounted for the effect of nicotine on endothelium-dependent vasodilatation were not examined. Thus the goal of this study was to examine the role of oxygen radicals in nicotine-induced impairment of arteriolar reactivity. We measured diameter of cheek pouch resistance arterioles (approximately 50 micrometer diameter) in response to endothelium-dependent (ACh and ADP) and -independent (nitroglycerin) agonists before and after infusion of vehicle or nicotine in the absence or presence of superoxide dismutase. ACh, ADP, and nitroglycerin produced dose-related dilatation of cheek pouch arterioles before infusion of vehicle or nicotine. Infusion of vehicle, in the absence or presence of superoxide dismutase (150 U/ml), did not alter endothelium-dependent or -independent arteriolar dilatation. In contrast, infusion of nicotine (2 microgram . kg-1 . min-1) impaired endothelium-dependent, but not -independent, arteriolar dilatation. In addition, the effect of nicotine on endothelium-dependent vasodilatation was reversed by topical application of superoxide dismutase. We suggest that nicotine impairs endothelium-dependent arteriolar dilatation via an increase in the synthesis/release of oxygen-derived free radicals.

Effect of cigarette smoke extract on arteriolar dilatation in vivo.

The goal of this study was to determine whether cigarette smoke extract alters dilatation of arterioles in vivo in response to agonists that produce activation of ATP-sensitive potassium channels and activation of adenylate cyclase. By using intravital microscopy, we measured diameter of arterioles contained within the microcirculation of the hamster cheek pouch during suffusion with agonists in the absence and presence of cigarette smoke extract (0.1, 0.5, and 1.0%). Before treatment with cigarette smoke extract, activation of ATP-sensitive potassium channels with aprikalim and cromakalim produced dose-related dilatation of cheek pouch arterioles. Similarly, activation of adenylate cyclase with isoproterenol and forskolin produced dose-related dilatation of cheek pouch arterioles before treatment with cigarette smoke extract. Superfusion of 0.1% cigarette smoke extract did not change baseline diameter of arterioles and did not alter responses of cheek pouch arterioles to activation of ATP-sensitive potassium channels and adenylate cyclase. Superfusion of 0.5 and 1.0% cigarette smoke extract also did not alter baseline diameter of arterioles but did impair dilatation of arterioles in response to activation of ATP-sensitive potassium channels and adenylate cyclase. These findings suggest that cigarette smoke extract impairs dilatation of resistance arterioles in response to activation of important cellular dilator pathways.