Biomedical subjects

K S Tan

Publications and source records attributed to K S Tan.

At least 37 records · Page 2Linked to original sources

PubMed1999

Beta2-adrenoceptor polymorphism and bronchoprotective sensitivity with regular short- and long-acting beta2-agonist therapy.

The aim of the present study was to investigate bronchoprotective sensitivity in patients receiving regular treatment with short- and long-acting beta2-agonists and to evaluate any possible association with genetic polymorphism. Thirty-eight patients with stable mild to moderate asthma and receiving inhaled corticosteroids were randomized in a parallel group, double-blind, double-dummy fashion to receive 2 weeks of treatment with either formoterol (12 microg once daily, 6 microg twice daily or 24 microg twice daily) or terbutaline (500 microg four times daily). Bronchoprotection against methacholine challenge (as a provocative dose to produce a 20% fall in forced expiratory volume in 1.0 s: PD20) was measured at baseline (unprotected) after an initial 1 week run-in without beta2-agonist, and at 1 h after the first and last doses of each treatment. The PD20 values were log-transformed and calculated as change from baseline. Percentage desensitization of log PD20 for first- versus last-dose bronchoprotection was calculated and analysed according to effects of treatment and beta2-adrenoceptor polymorphism at codon 16 or 27. The mean degree of desensitization for bronchoprotection was comparable with all four treatments and there were no significant differences in absolute PD20 values after 2 weeks of chronic dosing. The PD20 values were (as microg of methacholine, geometric means+/-S. E.M.): formoterol, 12 microg once daily, 99+/-42 microg; formoterol, 6 microg twice daily, 107+/-44 microg; formoterol, 24 microg twice daily, 108+/-45 microg; terbutaline, 500 microg four times daily, 88+/-37 microg. All patients receiving formoterol, 24 microg twice daily, exhibited a loss of protection greater than 30% which was unrelated to polymorphism at codon 16 or 27. For codon 16, the use of lower doses of formoterol (12 microg once daily or 6 microg twice daily) showed wider variability in the propensity for protection loss in patients who were heterozygous, in contrast to a more uniform protection loss seen with homozygous glycine patients. The amount of protection loss was not significantly related to polymorphism at codon 16 or 27, expressed as values (mean+/-S.E.M.) for percentage desensitization according to each genotype (pooled treatments): Gly-16, 66+/-11%; Het-16, 53+/-8%; Arg-16, 69+/-18%; Glu-27, 68+/-12%; Het-27, 58+/-8%; Gln-27, 52+/-12%. The results of this preliminary study showed that bronchoprotective desensitization occurred readily in response to short- or long-acting beta2-agonist exposure irrespective of beta2-adrenoceptor polymorphism at codon 16 or 27. Further studies with larger patient numbers are required to further evaluate the effects of polymorphisms with lower doses of regular formoterol.

Adolescent↗

PubMed1999

T wave alternans and acute rheumatic myocarditis: a case report.

T wave alternans is an uncommonly recorded cardiac rhythm. We report here an unusual case of a 13-year-old girl with acute rheumatic carditis and acute nephritis, who developed T wave alternans associated with a prolonged QT interval. These electrocardiographic changes were evident only after the initial acute stage of the disease process and should be borne in mind for patients with acute rheumatic carditis as they may be associated with more malignant arrhythmias.

Acute Disease↗

PubMed1999

Intracoronary brachytherapy: the beginning of the end of restenosis?

Restenosis remains a major problem 20 years after the introduction of coronary angioplasty. Pharmacological therapy has generally been disappointing in reducing the incidence of neointimal hyperplasia. Intracoronary brachytherapy is the latest anti proliferative agent that is showing promise in the fight against restenosis. Radiation therapy has been used for decades in the treatment of benign proliferative disorders. Animal studies have consistently demonstrated the efficacy of radiation therapy in inhibiting neointimal hyperplasia. Clinical trials, using different radioactive isotopes and radiation sources, are now showing dramatic reduction in neointimal hyperplasia and restenosis rates following balloon angioplasty and stenting. Intracoronary brachytherapy is beginning to show promise as one of the truly effective agent against neointimal hyperplasia and restenosis.

Animals↗

PubMed1999

Simultaneous EEG and ECG recording during a Stokes-Adams attack.

Simultaneous electroencephalographic and electrocardiographic recordings were obtained from a 77-year-old patient during a Stokes-Adams attack. The recordings showed a clear temporal relationship between symptoms, electroencephalographic and electrocardiographic changes during the Stokes-Adams attack. This case shows the usefulness of simultaneous EEG and ECG recordings in the investigation of patients with unexplained episodes of disturbed consciousness.

Adams-Stokes Syndrome↗

PubMed1998

Subsensitivity to bronchoprotection against adenosine monophosphate challenge following regular once-daily formoterol.

Regular treatment with inhaled long-acting beta2-agonists leads to subsensitivity to their bronchoprotective effects, although the effect of dosing frequency on this subsensitivity is not known. The aim of this study was to assess whether a once-daily dosing regimen with formoterol might be associated with a lesser degree of subsensitivity. In a randomized placebo-controlled double-blind, double-dummy crossover study 10 asthmatics treated with inhaled steroids (mean age 31 yrs, forced expiratory volume in one second (FEV1) 82% predicted) received 1 week of treatment with: formoterol dry powder 24 microg twice daily (08:00 and 20:00 h); formoterol 24 microg once daily (20:00 h); or identical placebo. Adenosine monophosphate (AMP) bronchial challenge was performed 12 h after the first and the last dose of each treatment. There was significant loss of protection with formoterol twice daily between the first and last dose (geometric mean provocative concentration causing a 20% fall in FEV1 (PC20)): 475 versus 129 mg x mL(-1) (a 3.7-fold loss, p=0.006) and with formoterol once daily: 367 versus 127 mg x mL(-1) (a 2.9-fold loss, p=0.005), compared with placebo: 71 versus 75 mg x ml(-1) (nonsignificant). There was no significant difference in the degree of loss of protection between formoterol once and twice daily. For first-dose protection there was a significant difference between active treatments and placebo, but after the last dose the residual protection between active treatments and placebo was not significant. Thus, in patients taking inhaled corticosteroids, regular formoterol 24 micreog once daily induces a similar degree of subsensitivity to adenosine monophosphate bronchial challenge as with formoterol 24 microg twice daily. This in turn suggests that even with a 24-h dosing interval there is the development of tolerance to formoterol by prolonged occupancy of airway beta2-adrenoceptors.

Adenosine Monophosphate↗

PubMed1998

Concomitant administration of low-dose prednisolone protects against in vivo beta2-adrenoceptor subsensitivity induced by regular formoterol.

STUDY OBJECTIVES: To assess whether concomitant administration of low-dose prednisolone (PRED) with regular inhaled formoterol (FM) might prevent the occurrence of beta2-adrenoceptor (beta2-AR) tachyphylaxis. DESIGN: Eleven healthy male subjects (mean age, 29 years) were randomized to receive 1 week with either inhaled FM, 24 microg bid, and placebo tablets (PL), or inhaled FM, 24 microg bid, and oral PRED, 15 mg daily, in double-blind, crossover fashion, with a 2-week washout between treatments. A dose-response curve (DRC) for systemic beta2-responses to inhaled salbutamol (800 to 3,200 microg) was constructed before and after each treatment period (ie, FM + PL or FM + PRED). Lymphocyte beta2-AR density (Bmax) and maximal cyclic adenosine monophosphate response to isoproterenol (isoprenaline) (Emax) were evaluated ex vivo at each visit; 8 AM serum cortisol level was also evaluated as a marker of systemic glucocorticoid activity. Comparisons for DRC were made as peak responses and area under curve (AUC). RESULTS: There was significant (p < 0.05) subsensitivity of systemic beta2-AR responses (as AUC) following FM + PL: for heart rate (before vs after), 760 vs 340 beats (95% confidence interval [CI], 160 to 680), for tremor 0.39 vs 0.19 log units/h (95% CI, 0.01 to 0.41), and for potassium, -0.34 vs -0.19 mmol x h/L (95% CI, -0.04 to -0.28). With PRED, there was protection against subsensitivity induced by FM with no significant difference in values before vs after FM: heart rate, 740 vs 640; tremor, 0.35 vs 0.34; and potassium, -0.30 vs -0.25. FM + PL induced significant downregulation of lymphocyte beta2-AR density (log Bmax; fmol/10(6) cells) (before vs after): 0.25 vs 0.11 (95% CI, 0 to 0.22; p < 0.05) and this was not altered by PRED (before vs after): 0.21 vs 0.10 (95% CI, 0.01 to 0.27; p < 0.05). FM + PL also caused desensitization of Emax (pmol/10(6) cells) (before vs after): 6.21 vs 2.29 (95% CI, 1.19 to 6.64; p < 0.05) and this was attenuated by PRED with no significant difference between before and after values: 4.60 vs 3.28. CONCLUSIONS: Concomitant administration of a low dose of PRED produced protection against FM-induced subsensitivity of systemic beta2-AR, as assessed by the response to inhaled salbutamol. In contrast, prednisolone did not prevent ex vivo beta2-AR downregulation despite causing significant cortisol suppression. This, in turn, suggests that there is a dissociation in the dose of PRED required to protect against beta2-AR downregulation and subsensitivity, following continuous exposure to long-acting beta2-agonist.

Administration, Inhalation↗

PubMed1998

Beta2-adrenoceptor regulation and function in female asthmatic patients receiving the oral combined contraceptive pill.

STUDY OBJECTIVES: Previously it has been shown that there is abnormal hormonal control of beta2-adrenoceptors in asthmatic women. Exogenous progesterone but not estradiol produces paradoxic downregulation and desensitization of beta2-adrenoceptors in asthmatic women when compared with nonasthmatic subjects. This study investigates the effect of the oral combined contraceptive pill (OCP) on beta2-adrenoceptor regulation and function in female asthmatic patients. PATIENTS: The study population was comprised of 11 women with stable mild to moderate asthma. The mean age was 25 years; the FEV1 was 89% of predicted, and the forced expiratory flow, mid-expiratory phase (FEF25-75%) was 69% of predicted. DESIGN: Patients were evaluated while on (day 20 to 21) and off (day 5 to 7) the OCP during a 28-day calendar period. MEASUREMENTS: Serum sex hormones, lymphocyte beta2-adrenoceptor parameters, and bronchodilator and systemic dose-response curves (DRCs) to albuterol (Salbutamol) (100 to 1,600 microg) were measured at both on and off periods. RESULTS: Serum levels of endogenous estradiol and progesterone were both suppressed by the OCP. Baseline FEV1 were not different while patients were on (2.70 L) and off (2.72 L) the OCP. There were no significant differences in lymphocyte beta2-adrenoceptor parameters between the two phases of the cycle. Receptor density (geometric mean Bmax) was 1.78 (on OCP) vs 1.86 (off OCP) fentomole/10(6) cells, maximal cyclic adenosine monophosphate response to isoprenaline was 6.60 (on OCP) vs 7.58 (off OCP) pmol/10(6) cells, and binding affinity was 14.0 (on OCP) and 13.6 (off OCP) pmol/L. Likewise, there were no significant differences in the bronchodilator and systemic DRCs constructed at both phases of the cycle as evaluated: area-under-curve (AUC) FEV1 was 0.53 (on OCP) vs 0.56 (off OCP) L.h; and AUC FEF25-75% was 3,130 (on OCP) vs 3,640 (off OCP) L. Potassium (K) and finger tremor responses were unaltered between the two periods: AUC K was 0.50 (on OCP) vs 0.44 (off OCP) mmol . h/L and AUC tremor was 0.72 (on OCP) vs 0.89 (off OCP) log units.h. CONCLUSION: The OCP did not alter beta2-adrenoceptor regulation and function in stable female asthmatic patients. Further studies are required in patients who have premenstrual asthma.

Adrenergic beta-Agonists↗

PubMed1997

Plasma homocysteine as a risk factor for vascular disease. The European Concerted Action Project.

CONTEXT: Elevated plasma homocysteine is a known risk factor for atherosclerotic vascular disease, but the strength of the relationship and the interaction of plasma homocysteine with other risk factors are unclear. OBJECTIVE: To establish the magnitude of the vascular disease risk associated with an increased plasma homocysteine level and to examine interaction effects between elevated plasma homocysteine level and conventional risk factors. DESIGN: Case-control study. SETTING: Nineteen centers in 9 European countries. PATIENTS: A total of 750 cases of atherosclerotic vascular disease (cardiac, cerebral, and peripheral) and 800 controls of both sexes younger than 60 years. MEASUREMENTS: Plasma total homocysteine was measured while subjects were fasting and after a standardized methionine-loading test, which involves the administration of 100 mg of methionine per kilogram and stresses the metabolic pathway responsible for the irreversible degradation of homocysteine. Plasma cobalamin, pyridoxal 5'-phosphate, red blood cell folate, serum cholesterol, smoking, and blood pressure were also measured. RESULTS: The relative risk for vascular disease in the top fifth compared with the bottom four fifths of the control fasting total homocysteine distribution was 2.2 (95% confidence interval, 1.6-2.9). Methionine loading identified an additional 27% of at-risk cases. A dose-response effect was noted between total homocysteine level and risk. The risk was similar to and independent of that of other risk factors, but interaction effects were noted between homocysteine and these risk factors; for both sexes combined, an increased fasting homocysteine level showed a more than multiplicative effect on risk in smokers and in hypertensive subjects. Red blood cell folate, cobalamin, and pyridoxal phosphate, all of which modulate homocysteine metabolism, were inversely related to total homocysteine levels. Compared with nonusers of vitamin supplements, the small number of subjects taking such vitamins appeared to have a substantially lower risk of vascular disease, a proportion of which was attributable to lower plasma homocysteine levels. CONCLUSIONS: An increased plasma total homocysteine level confers an independent risk of vascular disease similar to that of smoking or hyperlipidemia. It powerfully increases the risk associated with smoking and hypertension. It is time to undertake randomized controlled trials of the effect of vitamins that reduce plasma homocysteine levels on vascular disease risk.

Adult↗

PubMed1997

Effect of exogenous female sex-steroid hormones on beta 2-adrenoceptors in healthy males.

OBJECTIVE: We have previously demonstrated that exogenous progesterone, but not oestrogen, upregulated lymphocyte beta 2-adrenoceptors (beta 2-AR) when given during the follicular phase in healthy females. In the present study, we were interested to see whether this facilitatory effect of female sex-steroid hormones could be demonstrated in healthy males. METHODS: Nine healthy male volunteers with a mean age of 24 years completed this randomised, double-blind, placebo-controlled, cross-over study. They were randomised to receive either oral placebo, oestradiol valerate (4 mg) or medroxyprogesterone (40 mg). The study medication was given in two divided doses 12 h apart. Subjects attended the laboratory at baseline (T0 is baseline), 1 h after ingestion of the second dose of study medication (T1) and 24 h later (T24). At each visit, 60 ml of peripheral blood was withdrawn for measurement of serum oestradiol, progesterone and testosterone levels, and for lymphocyte beta 2-AR parameters; density (Bmax), binding affinity (Kd) and maximal cyclic AMP response to isoprenaline (Emax). RESULTS: Baseline levels of sex-steroid hormones were comparable for each of the treatment periods. Serum oestradiol levels increased significantly, twofold, 1 h after ingestion of oestradiol but there was no significant change in levels of serum progesterone and testosterone. Lymphocyte beta 2-AR parameters following treatment with oestradiol and progesterone did not change significantly from baseline and were not different from placebo. CONCLUSION: In contrast to previously reported effects in women, female sex-steroid hormones did not appear to have any significant facilitatory effects on lymphocyte beta 2-AR parameters when given exogenously to healthy males. This lack of effect may be due either to the absence of receptors for female sex hormones in beta 2-AR or to reduced efficacy of female hormone-receptor coupling in male lymphocytes.

Adult↗

PubMed1997

Effects of oral and inhaled corticosteroid on lymphocyte beta2-adrenoceptor function in asthmatic patients.

AIMS: We have previously demonstrated that a single dose of oral prednisolone but not single doses of inhaled fluticasone had facilitatory effects on lymphocyte beta2-adrenoceptor (AR) function. To address possible differences in steady-state time-course, the aim of this study was to determine if repeated dosing with inhaled fluticasone would have facilitatory effects on lymphocyte beta2-AR. Plasma cortisol was also evaluated as a measure of systemic bioactivity. METHODS: Ten asthmatic subjects, mean (s.e.mean) age 29 (3) years, FEV1 89 (5) % predicted, were randomised in a double-blind crossover study to receive inhaled placebo (PL), inhaled fluticasone 1000 microg day-1 (F1000) and inhaled fluticasone 2000 microg day-1, each for 4 days and also a single dose of oral prednisolone 50 mg (PRED). Prednisolone was given as open medication. The last dose of study drug was taken at 22.00 h and subjects attended the laboratory at 08.00 h the following day. RESULTS: beta2-AR density (Bmax; fmol/10[6] cells) was significantly increased after PRED compared with PL and inhaled fluticasone. Bmax (geometric mean) after each treatment were: PL 1.51, F1000 1.20, F2000 1.20 and PRED 2.14 (a 1.4 fold difference PRED vs PL; 95% CI 1.05 to 1.95; P < 0.001). There was significant (P < 0.001) suppression of plasma cortisol (nmol l-1) following F2000 and PRED compared with PL: 393.8, F1000 302.1, F2000 205.0 (95% CI F2000 vs PL 58.1 to 319.4) and PRED 87.0 (95% CI PRED vs PL 176.2 to 437.5). The estimated milligram equivalence ratio for adrenal suppression was calculated at 1:11 for fluticasone vs prednisolone. CONCLUSIONS: Repeated dosing with high-dose inhaled fluticasone did not up-regulate lymphocyte beta2-AR as compared with a single dose of oral prednisolone, despite having significantly suppressed early morning plasma cortisol. This study confirms our previous finding of a dissociation in sensitivity between effects of inhaled corticosteroid on adrenal suppression and lymphocyte beta2-AR regulation, at least for doses up to 2 mg day-1 of fluticasone.

Administration, Inhalation↗

PubMed1997

Loss of normal cyclical beta 2 adrenoceptor regulation and increased premenstrual responsiveness to adenosine monophosphate in stable female asthmatic patients.

BACKGROUND: A study was undertaken to investigate the influence of the menstrual cycle on airway responsiveness and beta 2 adrenoceptor function in female asthmatic patients. It has previously been shown that normal women exhibit cyclical changes in beta 2 adrenoceptor function with an increase in beta 2 adrenoceptor density in the luteal phase during the premenstrual period. METHODS: Fifteen women with stable, well controlled asthma (mean forced expiratory volume in one second (FEV1) 2.971 (93.8% predicted)) were evaluated. Measurements were made at the follicular phase (days 1-6) and the luteal phase (days 21-24) of the menstrual cycle. Airway responsiveness was assessed using adenosine 5'-monophosphate (AMP) and expressed as PC20 AMP. Beta 2 adrenoceptor function was evaluated by measuring lymphocyte beta 2 adrenoceptor parameters and constructing dose-response curves to salbutamol (100-1600 micrograms). The levels of female sex hormones were also measured at both phases of the cycle. RESULTS: There were significant increases in serum levels of both oestradiol (2.2-fold, p < 0.001) and progesterone (7.2-fold, p < 0.05) between the follicular and luteal phases. Geometric mean PC20 AMP was 19.0 mg/ml and 7.6 mg/ml during the follicular and luteal phases, respectively (p < 0.05), a 2.51-fold difference (95% CI 1.19 to 5.30) amounting to 1.33 doubling doses of AMP. There was no change in lymphocyte beta 2 adrenoceptor parameters or in airway beta 2 adrenoceptor responses to salbutamol between the two phases. CONCLUSIONS: Despite an appropriate rise in female sex hormones during the luteal period, beta 2 adrenoceptor regulation in female asthmatic subjects shows a loss of the normal cyclical pattern. In addition, there were cyclical changes in airway responsiveness to AMP which was highest during the premenstrual period. Thus, drugs such as theophylline which block adenosine receptors warrant investigation in premenstrual asthma.

Adenosine Monophosphate↗

PubMed1997

Modulation of airway reactivity and peak flow variability in asthmatics receiving the oral contraceptive pill.

Female sex-steroid hormones may play an important influence in asthma. The aim of this study was to compare airway reactivity to adenosine monophosphate (AMP) in female asthmatics with natural menstrual cycles and those taking the oral combined contraceptive pill (OCP). Eighteen asthmatic subjects were evaluated. Nine subjects, mean (SEM) age, 24 (6) years, FEV1 93% (10) predicted, with natural cycles (group 1) were compared with nine subjects, age 24 (6) years, FEV1 93% (9) predicted taking the OCP (group 2). Group 1 subjects were evaluated at the follicular (visit 1) and luteal (visit 2) phases; group 2 subjects were evaluated during the week off OCP (visit 1) and at the end of the OCP cycle (visit 2). At each visit, serum progesterone and estradiol were measured. Airway reactivity to AMP was evaluated and expressed as PC20 (FEV1; mg/ml). Morning and evening peak expiratory flow rates (PEFR) were monitored throughout the study. In group 1, there was a significant increase in serum progesterone (nmol/l) and estradiol (pmol/l). (Visit 1 vs. 2): 2.5 vs. 13.5 (95% CI 2.1 to 19.9; p = 0.02) and 152.3 vs. 358.1 (95% CI 113.0 to 298.5; p < 0.001), respectively. In group 2, however, there was no increase between visit 1 vs. 2 in hormones: 0.9 vs. 1.0 and 75.7 vs. 21.8 for progesterone and estradiol, respectively. There was a significant increase in airway reactivity in group 1 during the luteal phase. Geometric mean PC20 (mg/ml) was 18.8 and 4.7 at visit 1 and 2, respectively: a 4.0-fold difference (95% CI 1.25 to 13.03; p = 0.03) amounting to two doubling doses. In contrast, there was no change in PC20 in group 2. Geometric mean PC20 was 23.5 and 21.4: a 1.06-fold difference (95% CI 0.41 to 2.78; p = 0.83). In group 1, morning and evening PEFR (l/min) were significantly different at both visits: at visit 1 (A.M. PEFR vs. P.M. PEFR) 403 vs. 430 (95% CI 5 to 50; p < 0.001) and visit 2, 415 vs. 439 (95% CI 1 to 46; p < 0.001). In group 2, there was no significant difference in diurnal PEFR variability at both visits; 411 vs. 417 at visit 1 and 413 vs. 427 at visit 2. In conclusion, asthmatic patients receiving the OCP had attenuated cyclical change in airway reactivity as well as reduced diurnal PEFR variability, which was associated with suppression of the normal luteal phase rise in sex-hormones.

Adenosine Monophosphate↗

PubMed1997

Systemic corticosteriod rapidly reverses bronchodilator subsensitivity induced by formoterol in asthmatic patients.

There is evidence that downregulation and desensitization of airway beta 2-adrenoceptors (beta 2-AR) develops after continuous exposure to long-acting beta 2-agonists such as formoterol and salmeterol. To investigate the facilitatory effects of acute administration of systemic corticosteroid on bronchodilator subsensitivity, as might occur in the setting of acute asthma, 12 subjects with moderately severe asthma, with a mean FEV1 of 66% predicted, of whom were all receiving inhaled corticosteriod, were randomized to receive either inhaled placebo (PL) or inhaled formoterol (FM) 24 micrograms twice daily for 4 wk in a double-blind crossover study. Subjects were also genotyped in terms of beta 2-Ar polymorphism at loci 16 and 27. A dose-response curve (DRC) and duration-time profile for FM (12 to 108 micrograms) was produced 1 h after administration of placebo tablets and after injection at 3 wk, and 1 h after administration of oral prednisolone, 50 mg, and intravenous hydrocortisone, 200 mg, at 4 wk. Comparisons between treatments were made with area-under-curve (AUC) measurements as the change from baseline. There was a significant rightward shift in the DRC after FM as opposed to placebo for delta FEV1 (as AUC, L.h): 2.51 versus 4.22 (95% CI: 0.54 to 2.89; p = 0.01) and delta FEF25-75 (as AUC, L x 10(3)): 11.30 versus 19.94 (95% CI: 2.12 to 15.12; p = 0.01). This was significantly reversed by steroid (S) for FEV1 (FM versus FM+5): 2.51 versus 3.57 (95% CI: 0.11 to 2.27; p = 0.03) and for FEF25-75: 11.30 versus 18.47 (95% CI: 2.52 to 11.70; p = 0.005). Lymphocyte beta 2-AR density (log Bmax; fmol/10(6) cells) showed significant upregulation 3 h after steroid (FM+5 versus FM): 0.34 versus 0.24 (95% CI: 0.02 to 0.18; p = 0.01). For heart-rate response (as AUC, beats), there was subsensitivity with FM versus PL: 2,700 versus 5,200 (95% CI: 40 to 5,000; p < 0.001), and this was reversed by steroid (FM+5 versus FM): 9,600 versus 2,700 (95% CI: 4,900 to 8,800; p < 0.001). This reversal by systemic corticosteroid appears to be generally independent of beta 2-AR polymorphism at loci 16 and 27. In conclusion, we have demonstrated that bronchodilator subsensitivity occurs after regular inhaled FM in asthmatic patients, and is rapidly reversed by systemic corticosteroid. Thus, in acute asthma, systemic corticosteroid should be administered a soon as possible, in order to restore normal airway beta 2-AR sensitivity, particularly in patients who are receiving regular long-acting beta 2-agonists.

Adrenergic beta-Agonists↗

PubMed1997

Paradoxical down-regulation and desensitization of beta2-adrenoceptors by exogenous progesterone in female asthmatics.

We have demonstrated previously that exogenous progesterone, but not estrogen, up-regulated lymphocyte beta2-adrenoceptors (beta2-AR) when given during the follicular phase in healthy women. Female asthmatics exhibit loss of the cyclical pattern of beta2-AR regulation seen in healthy women, in that there is no luteal phase rise in beta2-AR. It has been postulated that abnormal cyclical regulation of beta2-AR might be a possible mechanism for premenstrual asthma. In this study, we were interested to see how exogenous female sex-steroid hormones altered beta2-AR regulation in female asthmatics during the follicular phase, when endogenous hormone levels are normally low. Seven nonsmoking female subjects with mild asthma, with a mean (SEM) age of 26 (2) years and FEV1 of 94.7% (6.4) of predicted, completed this randomized, double-blind, crossover study. They were evaluated at two successive menstrual cycles, during the follicular phase (day 1 to 6). They were randomized to receive single oral doses of either ethinyl estradiol (ethinyloestradiol), 50 microg, or medroxyprogesterone, 10 mg. Lymphocyte beta2-AR parameters were evaluated at baseline (T0), 24 h (T24), and 72 h (T72) after ingestion. Baseline levels of progesterone and estradiol were comparable on both cycles. Receptor binding density (log Bmax; fmol/10(6) cells) decreased significantly after progesterone but not after estrogen at T24: amounting to a 1.34-fold mean difference (95% confidence interval [CI], 1.01 to 1.78) between T24 vs T0 with progesterone. Comparing Bmax for progesterone with estrogen at T24 amounted to a 1.25-fold significant difference (95% CI, 1.00 to 1.56). This was associated with a trend (p=0.06) toward a lower cyclic-adenosine monophosphate (AMP) response to isoproterenol hydrochloride (isoprenaline) 10(-4) M (Emax) at T24 vs T0 with progesterone. Receptor binding affinity (Kd) was not altered by either treatment. These results show that exogenous progesterone, but not estrogen, given during the follicular phase, decreased beta2-AR density and cyclic-AMP response in female asthmatics, in contrast to the previously observed up-regulating effect of progesterone seen in healthy women. This paradoxical effect of progesterone in female asthmatics suggests an abnormal regulation of beta2-AR and might be a possible mechanism for premenstrual asthma when progesterone levels are high during this period of the cycle.

Administration, Oral↗

PubMed1996

Homocysteine and risk of premature coronary heart disease. Evidence for a common gene mutation.

BACKGROUND: Plasma homocysteine levels are modulated by nutritional and genetic factors, among which is the enzyme methylenetetrahydrofolate reductase (MTHFR). A common defective (thermolabile) variant of this enzyme is causally associated with elevated plasma homocysteine, itself an independent risk factor for coronary heart disease. METHODS AND RESULTS: To examine the hypothesis that the allele (T) that codes for the thermolabile defect increases the risk of coronary heart disease, we studied 111 patients with clinical and objective investigational evidence of coronary heart disease and 105 control subjects. The frequencies of the thermolabile defect (T) in patients and control subjects were measured, and the prevalence of elevated plasma total homocysteine according to genotype was assessed. The frequency of the defective allele was higher in patients than in control subjects with an OR of 1.6 (95% CI, 1.1 to 2.4; P = .02). The OR in the coronary heart disease group for the homozygous TT genotype was 2.9 (95% CI, 1.2 to 7.2; P = .02); 17% of patients and 7% of control subjects had the TT genotype. Plasma total homocysteine levels were significantly associated with disease status, a relationship that matched the strength of the association between disease and homozygous inheritance of the defective enzyme. CONCLUSIONS: Homozygotes for the defective allele (T) are at increased risk of premature coronary heart disease. MTHFR, which modulates basal plasma homocysteine concentration, is folate dependent, and dietary supplementation or fortification with folic acid may reduce plasma homocysteine levels and consequent coronary risk in a significant proportion of the general population.

Alanine↗

PubMed1996

Evaluation of plasma and urinary salbutamol levels in COPD.

OBJECTIVE: To evaluate the use of trough plasma salbutamol and overnight urinary salbutamol excretion in the assessment of nebulised salbutamol delivery in patients with chronic obstructive pulmonary disease (COPD). METHODS: Twenty in-patients with COPD receiving nebulised salbutamol, age 69.7 years, FEV1 38.1% predicted, were studied on two consecutive days, receiving four 2.5 mg doses of nebulised salbutamol on day 1 and four 5 mg doses of nebulised salbutamol on day 2, the first dose at 8.00 h the last dose at 22.00 h. Salbutamol delivery was assessed after the last dose by trough plasma salbutamol 8.00 h and overnight urinary excretion of salbutamol (22.00-8.00 h). RESULTS: Levels of urinary salbutamol were detectable in all 20 patients at both doses, whereas for plasma salbutamol detectable levels were only found in 16/20 cases at the 2.5 mg dose and in all cases at the 5 mg dose. For overnight urinary salbutamol (microgram x 10 h-1 n = 20) the results were 141 for 2.5 mg and 249 for 5 mg. The dose ratio for urinary salbutamol between 2.5 mg and 5 mg doses was 1.83. Results for plasma salbutamol (ng/ml, n = 16) were 1.58 at 2.5 mg and 2.43 at 5 mg: dose ratio (geometric mean) 1.49. CONCLUSION: Overnight urinary salbutamol provides a simple and effective measure of nebulised salbutamol delivery in patients with COPD, which would be suitable for studying nebuliser performance and compliance.

Administration, Inhalation↗

PubMed1996

Effects of exogenous female sex-steroid hormones on lymphocyte beta 2-adrenoceptors in normal females.

We have previously shown that lymphocyte beta 2-adrenoceptors (AR) are under cyclical control of sex-steroid hormones with greater receptor density during the luteal phase of the menstrual cycle. It has also been postulated that abnormal cyclical regulation of beta 2-AR might be a possible mechanism for premenstrual asthma. The effects of exogenous female sex-steroid hormones on lymphocyte beta 2-AR function were studied in eight normal healthy females. They were evaluated at two successive menstrual cycles, during the follicular phase (day 1-6). They were randomized to receive single oral doses of either ethinyloestradiol 50 micrograms or medroxyprogesterone 10 mg in a cross-over study. Lymphocyte beta 2-AR parameters were evaluated at baseline (t0), 24 h (t24) and 72 h (t72) after ingestion. Baseline levels of progesterone and oestradiol were comparable on both cycles. Receptor density (Bmax) increased significantly (P < 0.01) from t0 after progesterone but not oestradiol at t 4: a 1.39-fold geometric mean difference (95% CI 0.96-2.00) between t24 vs t0. Receptor affinity (kd) and maximal cAMP response to isoprenaline (Emax) were not altered by either treatment. These results show that exogenous progesterone but not oestradiol, given during the follicular phase, significantly increased beta 2-AR. This, therefore, suggests that endogenous progesterone is probably responsible for previously observed increase in Bmax during the luteal phase of the female menstrual cycle. These findings may suggest possible therapeutic strategies for modulation of beta 2-AR in premenstrual asthma.

Adult↗

PubMed1996

Effects of inhaled fluticasone propionate and oral prednisolone on lymphocyte beta 2-adrenoceptor function in asthmatic patients.

The aim of the study was to evaluate the facilitatory effects of inhaled corticosteroid on in vitro parameters of lymphocyte beta 2-adrenoceptor function in asthmatic patients. Serum cortisol level was also evaluated as a measure of systemic bioactivity. Ten (four female) asthmatic subjects were evaluated, mean (SEM) age was 28.6(2.0) years, and FEV1 was 79.9%(8.7) predicted. Single doses of inhaled placebo (PL), fluticasone propionate, 1,000 micrograms (F1000), fluticasone propionate, 2,000 micrograms(F2000), or oral prednisolone, 50 mg(PRED), were given at 10 PM the previous night and measurements were made 10 h later. Values for beta 2-receptor density (logBmax: fmol/10(6)cells) were significantly (p < 0.05) greater than PL with PRED but not with inhaled fluticasone (as means and 95% confidence interval [CI] for difference vs PL): PL, 0.27; F1000, 0.30; F2000, 0.32; and PRED, 0.48 (95% CI vs PL, 0.075 to 0.341). Maximal cyclic adenosine monophosphate (cAMP) responses to isoproterenol hydrochloride (isoprenaline (Emax; pmol/10(6)cells) mirrored those for Bmax: PL, 4.00; F1000, 4.68; F2000, 4.26; and PRED, 7.46 (95% CI vs PL, -0.01 to 6.91). Receptor affinity (Kd) was not significantly altered by any treatment. There was significant (p < 0.05) suppression of serum cortisol (nmol/L) with F2000 and PRED compared with PL: PL, 307.9; F1000, 323.2; F2000, 130.1 (95% CI vs PL, 69.76 to 285.8) and PRED, 51.8 (95% CI vs PL, 144.11 to 368.01). Thus, high-dose inhaled fluticasone propionate did not have any facilitatory effects on lymphocyte beta 2-adrenoceptor parameters as compared with oral prednisolone which upregulated beta 2-receptor density and increased cAMP response. In contrast, high-dose inhaled fluticasone (2,000 micrograms) significantly suppressed serum cortisol. In conclusion, there would appear to be a dissociation in systemic sensitivity between effects of inhaled corticosteroid on adrenal suppression and lymphocyte beta 2-adrenoceptor regulation.

Administration, Topical↗