Molecular interactions between fenoterol stereoisomers and derivatives and the beta(2)-adrenergic receptor binding site studied by docking and molecular dynamics simulations.
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Bronchodilator action of inhaled fenoterol and ipratropium in normal subjects: a teaching exercise for medical students.
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1. A pharmacology practical class for preclinical medical students was designed as a placebo-controlled, double-blind trial of two bronchodilator drugs. 2. Fenoterol hydrobromide (800 micrograms), ipratropium bromide (80 micrograms) and placebo (propellant only) were given by metered dose inhaler to 79 non-asthmatic volunteers. Their effects on FEV1, heart rate and tremor (assessed by the time taken to thread five sewing needles) were compared. 3. Both drugs caused a significant increase in FEV1: the largest group mean increase was 77 ml, recorded 15 min after fenoterol, and 103 ml, recorded 60 min after ipratropium. 4. Fenoterol also caused a mean increase of 8.7 beats min-1 in heart rate, 5 min after inhalation. This effect was still apparent after 60 min. 5. Fenoterol appeared to prolong needle threading time in some individuals. 6. In subjects who inhaled fenoterol, there were no correlations between the increase in FEV1, the increase in heart rate, or the development of tremor. 7. It is concluded that inhaled fenoterol and ipratropium both cause bronchodilation in normal subjects. Systemic absorption of fenoterol is indicated by the rapid increase in heart rate. The bronchodilator effect of ipratropium suggests that resting airway calibre is governed partly by parasympathetic tone in normal subjects. 8. The bronchodilator and systemic effects of these drugs can be used to demonstrate pharmacological, therapeutic and statistical principles to medical students. (+info)
Effects of atenolol vs diltiazem on the haemodynamic effects of an inhaled beta 2-adrenoceptor agonist.
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To determine the effects of concurrent beta 1-adrenoceptor blocker or calcium channel antagonist administration on the haemodynamic sequelae of an inhaled beta 2-selective adrenoceptor agonist bronchodilator, we examined echocardiographically the effects of fenoterol (400 micrograms) by metered dose inhaler following oral pre-treatment with (a) placebo, (b) atenolol or (c) diltiazem. Following placebo, fenoterol produced significant decreases in diastolic blood pressure (14% +/- 6%), total peripheral vascular resistance (TPR) (31% +/- 9%) and end-systolic stress (ESS) (15% +/- 21%). Cardiac output rose significantly (42% +/- 23%) as did heart rate (25% +/- 13%). After atenolol, responses to fenoterol were significantly blunted. Post-fenoterol heart rate, systolic blood pressure, % fractional shortening, stroke volume, ejection fraction, cardiac output and pressure/volume ratio increased significantly less after atenolol pre-treatment as compared to placebo pretreatment. TPR decreased significantly less. After diltiazem pre-treatment, the response to inhaled fenoterol was not different from that following placebo pre-treatment. We conclude that atenolol blunts the haemodynamic changes induced by fenoterol inhalation whereas diltiazem has little effect. (+info)
Hypokalaemia and other non-bronchial effects of inhaled fenoterol and salbutamol: a placebo-controlled dose-response study in healthy volunteers.
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1. The hypokalaemia-inducing effects of two widely used inhaled antiasthmatic beta 2-adrenoceptor agonists, fenoterol and salbutamol, were compared in six healthy male volunteers. 2. Each drug was administered in three different doses, 400, 600 and 800 micrograms, which were repeated three times with 30 min intervals (total doses 1200, 1800 and 2400 micrograms in 1 h). The treatments were given at 1 week intervals in random order in a single-blind fashion. 3. The concentration of potassium in plasma was dose-dependently reduced by both drugs with peak effects 75-90 min after the first inhalations. The hypokalaemic effect of fenoterol was significantly greater than that of equal doses of salbutamol (average +/- s.d. reductions of 1.13 +/- 0.32 and 0.67 +/- 0.25 mEq l-1, respectively, after the highest doses, P less than 0.05). Concomitantly, decreases were noted in the amplitude of the T-wave on the ECG. 4. The concentration of cyclic AMP in plasma was measured and used as an indicator of systemic beta 2-adrenoceptor agonistic effects of the drugs. Increases in cAMP were a close mirror image of the drugs' effects on potassium in plasma. 5. Plasma renin activity, noradrenaline in plasma and heart rate were also dose-dependently increased by the treatments, whereas blood pressure remained unaltered. 6. While the clinical significance of hypokalaemia induced by inhaled beta 2-adrenoceptor sympathomimetics still is a matter of debate, our results point to possible differences between therapeutically equipotent doses of fenoterol and salbutamol in their propensity to cause hypokalaemia and other acute non-bronchial effects. (+info)
Responses to the beta 2-selective agonist procaterol of vascular and atrial preparations with different functional beta-adrenoceptor populations.
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Relaxant responses to the beta-adrenoceptor agonist, procaterol, have been examined on preparations of guinea-pig pulmonary artery (beta 2-adrenoceptors only), rat and rabbit pulmonary artery and rat aorta (beta 2 greater than beta 1), and these responses have been compared with responses of dog left circumflex coronary artery (beta 1 only). Low concentrations of procaterol (3 nM to 100 nM) relaxed KC1-contracted preparations of rat aorta and pulmonary artery from rat, rabbit and guinea-pig whereas high concentrations (greater than 1 microM) were required to relax preparations of the dog left circumflex coronary artery. The dissociation constant (KP value) for procaterol on beta 1-adrenoceptors was 4.9 microM (determined on dog coronary artery) and on beta 2-adrenoceptors was 0.008 microM (rabbit pulmonary artery). Procaterol therefore had a beta 2:beta 1 selectivity value of 612. KP values obtained on guinea-pig atria for procaterol, on which the concentration-response curve was biphasic, confirmed that both beta 2- and beta 1-adrenoceptors mediate responses of this tissue. The KP values were 0.009 microM (data from the first phase of the control concentration-response curve) and 3.5 microM (data from the concentration-response curve in the presence of the beta 2-selective antagonist, ICI 118,551, 10 nM). Data obtained on rat atria indicated that chronotropic responses of preparations from some rats, but not others, involved a minor population of beta 2-adrenoceptors, but the beta 2-adrenoceptors, when present, were less important than in guinea-pig atria. 6 Procaterol appears to be a particularly useful drug for detecting a functional population of beta 2-adrenoceptors in tissues, whether they are the minor or the predominant receptor sub-type present. (+info)
The costo-uterine muscle of the rat contains a homogeneous population of beta-adrenoceptors.
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The effects of two selective beta-adrenoceptor antagonists on the inhibitory responses to some sympathomimetic amines of electrically-stimulated preparations of costo-uterine muscle, taken from virgin rats, have been examined quantitatively. pA2 values for the antagonist, atenolol (beta 1-selective) and ICI 118,551 (beta 2-selective) were obtained using as agonists, fenoterol (beta 2-selective agonist) and noradrenaline (alpha- and beta-adrenoceptor agonist, beta 1-selective); and in addition, with ICI 118,551 only, isoprenaline (beta-agonist, non-selective) and adrenaline (alpha- and beta-adrenoceptor agonist, beta 2-selective). Catecholamine uptake mechanisms and alpha-adrenoceptors were not blocked in any of these experiments. Atenolol competitively antagonized the effects of fenoterol and noradrenaline to a similar extent, the pA2 values being 5.4 and 5.7, respectively. ICI 118,551 competitively antagonized the effects of fenoterol, isoprenaline, adrenaline and noradrenaline to a similar extent; pA2 values ranged from 8.7 with noradrenaline to 9.1 with isoprenaline. These results extend our previous observations which indicated that the adrenoceptors mediating inhibition of electrically-evoked contractions of costo-uterine muscle of the virgin rat are homogeneous and of the beta 2-subtype. The potency of the beta 1-selective agonist RO 363 in producing inhibition of electrically-evoked contractions of this tissue was also examined. RO 363 was 200 times less potent than isoprenaline but was a full agonist. This indicates that there is efficient coupling between beta 2-adrenoceptor activation and tissue response in this non-innervated preparation. (+info)