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PubMed1989

Central adrenoceptors and basal prolactin release in the rat.

The influence of the central adrenergic system on basal prolactin secretion was investigated in the rat. Several selective adrenoceptor blockers were centrally administered and their effects on prolactin secretion were observed. Blockade of beta-1 receptors by practolol, beta-2 receptors by IPS 339 and alpha-2 receptors by DG-5128 did not modify basal prolactin secretion, but alpha-1 adrenoceptor blockade by prazosin strongly enhanced prolactin plasma levels. These findings suggest that noradrenergic pathways in the central nervous system exert inhibitory tone on basal prolactin secretion, and that this effect seems to be mediated by alpha-1 adrenoceptors.

Adrenergic beta-Antagonists↗

PubMed1980

Characterization of the beta-adrenergic receptor mediating secretion of parathyroid hormone.

In vitro incubation studies with bovine parathyroid gland slices compared the relative responsiveness of parathyroid hormone (PTH) secretion to isoprotherenol, epinephrine or norepinephrine. Isoproterenol was the most potent and norepinephrine the least potent of the three stimuli, suggesting a beta 2 type of an adrenergic response. However in this in vitro system, tazalol, a selective beta 1 adrenergic agonist significantly stimulated PTH secretion, whereas terbutaline, a selective beta 2 agonist had no effect. In addition, practolol, a selective beta 1 adrenergic antagonist blocked isoproterenol- or tazolol-stimulated PTH secretion. In vivo studies in normal human subjects showed that injection of te nonselective beta agonist, isoproterenol, (0.15 mg s.c.) significantly increased, whereas injection of the selective beta 2 agonist, terbulatine (0.3 mg s.c.) had no effect on serum PTH levels. These latter studies with putative selective beta adrenergic agents suggest that the beta adrenergic receptor mediating PTH secretion is of the beta 1 type (in contrast to the studies above with nonselective agents). The studies suggest that the beta adrenergic receptor mediating PTH secretion apparently differs from the classical beta 1 receptor described in th myocardium or the classical beta 2 receptor described in the bronchial smooth muscle.

Adrenergic beta-Agonists↗

PubMed1980

Effects of salbutamol and butoxamine on the human fat cell adenylate cyclase.

In order to characterize the beta-adrenoceptors coupled to the human fat cell adenylate cyclase more extensively the effects of the beta 2-selective agonist salbutamol on basal and isoproterenol-stimulated rates of cAMP-accumulation were studied. Although exhibiting only low intrinsic activity salbutamol displayed only slightly lower affinity towards the beta-adrenoceptors linked to the human fat cell adenylate cyclase than isoproterenol. In addition, the beta 2-selective antagonist butoxamine was slightly more potent in inhibiting the isoproterenol-stimulated fat cell enzyme than the cardioselective beta-blocking agent practolol. These results further emphasize the difficulties in classifying the lipolytic response of adipose tissue to beta-adrenergic agonists and antagonists within a uniform beta-receptor theory.

Adenylyl Cyclases↗

PubMed1991

Beta adrenoceptors mediate the catecholamine-induced stimulation of oxytocin secretion from cultured bovine granulosa cells.

Bovine granulosa cells were treated in culture with alpha- and beta-adrenoceptor ligands to determine the receptor subtype mediating their response to catecholamines. The secretion of oxytocin by granulosa cells in serum-free medium was measured on the fourth day of culture (during the period of acquisition of a luteal phenotype). Cultures were performed in the presence of 0.5 mM ascorbic acid, which increased hormone output and potentiated the response to catecholamines. The effects of adrenaline and noradrenaline on oxytocin secretion were concentration-dependent; maximum stimulation was over 700% with adrenalin (EC50 92 nM) and 500% with noradrenaline (EC50 87 nM). The response to noradrenaline (10(-6) M) and adrenaline (10(-6) M) could be blocked by propranolol but not by phentolamine, suggesting that beta- rather than alpha-adrenoceptors were involved. Blockade by metoprolol and practolol (beta 1-adrenoceptor antagonists) was poor and dobutamine (beta 1-agonist) was weakly stimulatory. A concentration-dependent stimulatory response (EC50 200 nM) was obtained with salbutamol (beta 2-adrenoceptor agonist) and stimulation by adrenaline or salbutamol could be blocked by a selective beta 2-adrenoceptor antagonist (ICI 118,551). It is concluded that, during luteinization, the long-term response of bovine granulosa cells to stimulation induced by catecholamines is mediated through beta- rather than alpha-adrenoceptors. Although the beta 2-subtype is probably involved, the similar potencies of adrenaline and noradrenaline are uncharacteristic of beta 2-adrenoceptors and may be peculiar to the long-term response shown by these cells.

Adrenergic alpha-Antagonists↗

PubMed2000

Investigation of the metabolism of 14C/13C-practolol in rat using directly coupled radio-HPLC-NMR-MS.

1. The metabolic fate of 14C/13C-practolol was investigated using on-line HPLC-NMR-MS following oral administration to rat. The major route of elimination for the radiolabel was via the urine with the principal biotransformation products confirmed as the 2-hydroxy- and 2-hydroxyglucronide metabolites. 2. In addition, futile deacetylation, determined by the replacement of 13C-labelled acetyl groups with endogenous 12C-acetyls accounted for approximately 7-10% of the urinary metabolites, corresponding to approximately 5% of the dose undergoing N-deacetylation. 3. Evidence for chiral metabolism was sought via NMR of isolated metabolites using beta-cyclodextrin as a chiral shift agent. Practolol was excreted as a racemate. However, some enantioselective metabolism/excretion had occurred as the hydroxy- and hydroxyglucuronide were not excreted as racemic mixtures. 4. Directly coupled radio-HPLC-NMR-MS is extremely effective for the identification of the metabolites of radiolabelled xenobiotics in urine samples.

Adrenergic beta-Antagonists↗

PubMed1977

The effect of ageing on drug absorption from the gut.

Single oral doses of aspirin and practolol were given to young and old subjects. The results of the plasma concentration-time curves were subjected to pharmacokinetic appraisal. There was no difference with either drug between the two age-groups in the mean absorption rate constant and the time at which maximum concentration in the plasma occurred. However, the amount of drug in the plasma of the elderly group was the same or higher than that in the younger group. It is concluded that ageing has no significant effect on the rate or amount of these drugs absorbed.

Administration, Oral↗

PubMed1978

Effects of oral equiblocking doses of a cardioselective and noncardioselective beta-adrenergic blocking agent on left ventricular function in the normal conscious dog.

The effects of propranolol, a noncardioselective beta-adrenergic blocking agent, and practolol, a cardioselective agent, on left ventricular function were compared in an awake dog model at an equiblocking dose range. Both agents produced modest depression of inotropic state at rest, and during volume and phenylephrine loading. No significant differences between the two agents were detected.

Animals↗

PubMed1988

Alterations in the cellular DNA and protein content determined by flow cytometry as indicators for chemically induced structural and numerical chromosome aberrations.

Cellular DNA and protein content were determined simultaneously in freshly isolated fibroblast-like rat cells by flow cytometry. After exposure to doxorubicin, nitrofurantoin, propranolol and practolol at a low, tissue like oxygen concentration (5% O2), drug-induced alterations in cell cycle kinetics, in the distribution of DNA and in the protein content of G1-phase cells (nucleus/cytoplasm ratio) were analysed. Optimal exposure time (5 or 24 h) and recovery interval (24 or 48 h) were determined. Variation in the exposure time and recovery period can affect cell cycle kinetics both qualitatively and quantitatively, whereas the distribution of DNA and protein content are affected quantitatively only. A 24-h exposure combined with a 24-h recovery period proved to be the most efficient approach. Each of the tested chemicals induced a specific, dose-dependent pattern of altered cellular DNA and protein content. Comparison with results obtained in other genotoxicity tests, and with data reported earlier, showed that this two-parameter protocol can be used to recognize and to characterize chemicals as clastogens, or as compounds with a combined cytostatic/clastogenic activity, or as spindle-poison-like compounds.

Animals↗

PubMed1976

Studies of the dual effects of halothane on the lipolysis of human fat cells.

Halothane has dual effects on lipolysis of human adipose tissue: at low tissue concentrations a stimulatory effect is found, while at higher tissue concentrations lipolysis is inhibited. The lipolytic resonse of human adipose tissue was studied in vitro with or without halothane, the phosphodiesterase inhibitor theophylline, the lipase activator dibutyryl cAMP(dbcAMP), the alpha-receptor antagonist phentolamine, the nonselective beta-receptor antagonist propranolol, and the selective beta1-receptor antagonist practolol. In the absence of beta-receptor antagonists low concentrations of halothane stimulated lipolysis, This effect was blunted by beta-receptor antagonists, indicating that halothane at low tissue concentrations may directly stimulate the beta-receptors. The inhibitory effect of higher tissue concentrations of halothane was not the result of increased alpha-receptor activity since addition of phentolamine did not inhibit this effect. High concentrations of theophylline or dbcAMP increased lipolysis in specimens exposed to halothane, but the lipolytic rate was still less than that found in specimens not exposed to halothane. The data thus indicate that the inhibitory effect of halothane is exerted at a step beyond the formation and degradation of cAMP.

Adipose Tissue↗

PubMed1992

Penetrating keratoplasty for bilateral acute corneal calcification.

A 76-year-old man with bilateral practolol-induced dry eyes developed atypical acute bilateral corneal calcification. Serum calcium, phosphate, and urea levels were within normal limits. The calcium deposition progressed rapidly to involve 90% of the right cornea. Right penetrating keratoplasty was performed with subsequent visual rehabilitation of the patient. Left tectonic penetrating keratoplasty was performed 8 weeks later after corneal perforation. The corneal specimens were examined by light and electron microscopy, which showed an atypical calcareous degeneration involving Bowman's layer as well as the full thickness of the stroma. Transmission electron microscopy showed the granular calcification to consist of extracellular, radially orientated aggregates of fine, needle-shaped crystals. Both transplants remained clear with no evidence of postoperative recurrence. To our knowledge this is the first report of bilateral penetrating keratoplasty for acute calcareous degeneration.

Aged↗

PubMedDate not supplied

Induction by histamine of oscillatory activity in sheep Purkinje fibers and suppression by verapamil or lidocaine.

Histamine (1--2 x 10(-5) M) induced or enhanced oscillatory activity in four of five sheep Purkinje fibers depolarized by a low-potassium medium. These effects of histamine were readily antagonized by 2 x 10(-5) M burimamide but were unaffected by 10(-5) M practolol. Oscillatory activity was consistently induced or enhanced by 5 x 10(-6) M adrenaline in five preparations. Oscillatory activity, whether induced by histamine or adrenaline, was always abolished by verapamil (0.22--2.2 x 10(-6 M) but in only one of five experiments by lidocaine (4.2 x 10(-5) M). We conclude that induction of oscillatory responses may be added to the other arrhythmogenic mechanisms produced by histamine through the stimulation of H2 receptors. We confirmed that oscillatory activity is very effectively suppressed by verapamil.

Action Potentials↗

PubMedDate not supplied

Effect of chronic beta-blockade on the ischaemic myocardium: a comparative study with five drugs.

The long-term effects of chronic beta-blockade in the rat myocardium were investigated in terms of responses to ischaemic stress. Clinically relevant and equipotent doses of oxprenolol, propranolol, metoprolol, atenolol, and practolol were administered orally for 12 weeks. Twenty-four hours after the last dose, at a time when plasma drug levels were undetectable, hearts were excised and perfused as isolated preparations. During a 3-h period of low-flow, global ischaemia, the time to electromechanical failure following the onset of ischaemia was significantly increased in hearts from animals treated with drugs possessing intrinsic sympathomimetic activity (ISA). Similarly, with ischaemia-induced lactate and enzyme release, hearts from groups treated with drugs possessing ISA showed an increase in release above that of controls, or of hearts from rats treated with beta-blockers which did not possess ISA. These results suggest that in the isolated, globally ischaemic heart, when exogenous catecholamine drive is absent, long-term beta-blockade cannot exert a protective effect when circulating drug levels are undetectable, and compounds possessing ISA may increase tissue damage as measured by lactate and enzyme leakage.

Adrenergic beta-Antagonists↗

PubMedDate not supplied

Effect of dopamine and blockade of dopaminergic and adrenergic receptors on coronary blood flow in ischemic rabbit myocardium.

The effect of a broad dose range of dopamine on coronary blood flow was studied in rabbits with coronary artery occlusion. Dopaminergic and adrenergic receptor blockade was established to distinguish the mechanism of the dopamine-induced increase in coronary blood flow. Dopamine, 10, 100, or 1,000 micrograms/kg/min, was infused in the presence of dopaminergic, beta-, or alpha-adrenergic receptor blockade. Coronary blood flow, as measured by radiolabeled microspheres, and hemodynamic parameters were monitored in 60 anesthetized open-chest rabbits. Dopamine, 1,000 micrograms/kg/min, significantly increased coronary blood flow 157% in normal and 118% in occluded rabbit myocardium. Propranolol (2 mg/kg) prevented the dopamine-induced increases in coronary blood flow within occluded and nonoccluded myocardium. Practolol (2 mg/kg) blunted the coronary blood flow increases within occluded myocardium, but flow within normal myocardium remained significantly elevated. In animals given phenoxybenzamine (2 mg/kg), dopamine infusion produced significant blood pressure reductions along with no change in either occluded or nonoccluded coronary blood flow. Bulbocapnine (8 mg/kg), a dopamine receptor antagonist, did not block blood flow increases in normal myocardium, but prevented significant increases in blood flow within occluded myocardium. It can be concluded that direct or indirect vasodilator receptors (dopaminergic, beta 1-, and beta 2-adrenoceptors) must be stimulated and perfusion pressure must not fall in order for dopamine to produce increases of coronary blood flow within occluded myocardium.

Animals↗

PubMed1976

Double-blind study of the effect of cardioselective beta-blockade on chest pain in acute myocardial infarction.

A double-blind study including three different cardioselective beta-blockers, practolol, H 87/07 and metoprolol, was performed in 54 patients with acute myocardial infarction and chest pain shortly after onset of symptoms. Transmural infarctions were found in 42 patients while 12 patients had nontransmural infarctions. Chest pain and the product of heart rate and systolic blood pressure were significantly reduced in the beta-blocker groups whereas no changes were seen after saline. All patients with nontransmural infarctions and 14 out of 29 with transmural infarctions got pain relief lasting for at least 30 min. None of the patients developed signs of left ventricular backward failure, shock, or bradycardia. A decrease in ST segment elevation was observed in all the transmural infarctions after beta-blockade. No changes in ST segment elevation were found after analgesics when given after saline, but in some cases an increase was seen in this parameter when analgesics were given due to insufficient pain relief after beta-blockers or due to return of chest pain. It is suggested that pain relief by beta-blockers indicates decrease of myocardial ischemia.

Acute Disease↗

PubMed1981

Beta blockade and the secondary prevention of myocardial infarction.

In 1965 Snow reported a clinical trial in which treatment with propranolol significantly reduced mortality following myocardial infarction. Unfortunately the design of this trial was inadequate by modern standards, and the results must be discounted. None of the studies published since then have provided convincing evidence that beta blockers are useful following myocardial infarction. Survival after a myocardial infarction depends principally upon the amount of heart muscle that has been destroyed, and it is probably unreasonable to expect any treatment to reduce mortality by more than 20 or 30%. In patients who survive an infarction for more than 48 hours, the expected fatality rate in the next year is approximately 15%. To detect a reduction of this mortality to 10%, 2300 patients would be needed in the trial. The analysis of several of the published trials has been made difficult by a lack of data, the failure on the part of authors and journal editors to agree on a common method of presenting results, and disagreement as to whether results should be analysed on an "all patients--intention to treat" basis or by considering only "clinical effectiveness" among patients who remained on treatment. Examples of these problems will be given, together with a suggested scheme for data presentation. The 95% confidence intervals of all the randomised and double blind studies of beta blockers after myocardial infarction show that by "intention to treat" analysis, none demonstrate a statistically significant reduction in mortality among treated patients. Only the practolol trial was of a reasonable size, but even here total mortality was not significantly reduced; the result is in any case of only theoretical interest. The trials showing a reduction of mortality in association with alprenolol treatment are not convincing, and the stratified trial design of one of these may have given misleading results because of the relatively small number of patients involved.

Adrenergic beta-Antagonists↗

PubMed1983

Absorption of beta-adrenoceptor antagonists to Amberlite resin.

The adsorption of beta-adrenoceptor blockers and the partial beta-adrenoceptor agonist prenalterol was studied in an in vitro haemoperfusion (HP) model. Metoprolol, alprenolol, propranolol and prenalterol adsorb well from the blood to the resin with extraction ratios nearing 1.0. Extraction ratio for practolol was 0.68 and for atenolol 0.49. Protein binding has little effect on the degree of adsorption, which is more dependent on water solubility.

Adrenergic alpha-Antagonists↗

PubMed1983

An assessment of physiological finger tremor as an indicator of beta-adrenoceptor function.

Physiological finger tremor has been assessed as an indicator of beta-adrenoceptor function. Tremor was not correlated with the sex, age, weight or height of the subjects and was stable over 5 min when the hand and fingers were held horizontally. It was not increased by mental arithmetic, the Valsalva manoeuvre or 3 min exercise. Satisfactory dose-response curves could be constructed for the isoprenaline enhanced increases in finger tremor. In six subjects, practolol 120 mg produced a small shift to the right of the isoprenaline dose-response curve for finger tremor (dose ratio 2.1) but propranolol 40 mg was seven times more effective (dose ratio 17.1). Physiological finger tremor appears to be a stable parameter which may be useful in the investigation of the selectivity of beta-adrenoceptor blocking drugs.

Adult↗

PubMed1975

Urticaria and hyperthyroidism.

A thyrotoxic patient presented with urticaria and this appeared to respond to beta-blockade with practolol. Symptoms did not recur when radioactive iodine treatment took effect in spite of stopping the beta-blocker. Possible mechanisms are discussed and it is stressed that more emphasis should be placed on this association.

Adult↗