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PubMed1983

In vitro study of phosphodiesterase-inhibiting drugs: a complement to beta-sympathomimetic drug therapy in premature labor?

Since terbutaline treatment in premature labor has been shown to increase phosphodiesterase activity in the myometrium, the phosphodiesterase-inhibiting effect of theophylline and papaverine on myometrial preparations from pregnant women has been studied. The patients were either treated with terbutaline during the last 3 weeks of pregnancy or not treated. The results showed that papaverine is about 100 times more potent than theophylline in both phosphodiesterase-inhibiting effect and muscle-relaxing effect. No differences in effects were found in myometrial strips from terbutaline-treated or untreated women. A possible improvement in the tocolytic therapy with a combination of a beta-sympathomimetic and a phosphodiesterase-inhibiting drug is suggested.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Salivary secretion induced from isolated, perfused rat submandibular glands by sympathomimetic agents.

Saliva secretion was elicited from the isolated preparations by isoproterenol and phenylephrine, at concentrations from 10(-8) to 10(-5) M. The volumes of saliva secreted during a 60-min period, the rates of flow and the electrolyte composition of saliva secreted in response to each secretagogue were similar to those in vivo. Replacement of perfusate Na+ inhibited the secretion of fluid induced by isoproterenol (75 per cent) and by phenylephrine (99 per cent). It also reduced the Na+ and K+ concentrations of saliva elicited by the two secretagogues and inhibited isoproterenol-induced protein secretion (81 per cent). Omission of Ca2+ from the perfusate also inhibited fluid secretion (isoproterenol-stimulated, 84 per cent; phenylephrine-stimulated, 99 per cent) and isoproterenol-induced protein secretion (69 per cent). The absence of the divalent cation in the perfusate resulted in increased Na+ and decreased K+ concentrations in isoproterenol-stimulated saliva and in reduced K+ concentrations in phenylephrine-stimulated saliva. Administration of 10(-5) M phentolamine did not modify the volume of saliva secreted in response to isoproterenol, but reduced the response to phenylephrine by 90 per cent. The antagonist caused some reduction in the Na+ and K+ concentrations of isoproterenol-stimulated saliva, but did not modify those of phenylephrine-evoked secretion. Little recovery in fluid secretion was observed when the isolated gland was perfused with complete perfusate in the presence of phenylephrine after perfusion with Na+- or Ca2+-free solutions. Thus perfused rat submandibular glands are fully functional preparations, which respond to sympathomimetic agents of the alpha and beta types.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

A comparison of the effects of different methods of administration of beta-2-sympathomimetics in patients with asthma.

Double-blind cross-over studies of oral and inhaled terbutaline and salbutamol have been performed in two groups of asthmatic patients. Both drugs at the doses recommended by the manufacturers produced similar maximal effects. The onset of response was faster with inhaled treatment and there was no difference in length of action between the drugs or the routes of administration. Side-effects were much more common with oral treatment. In a separate study oral and inhaled terbutaline were compared in 11 asthmatic patients and this also showed a similar maximal response in tests of forced expiration. A greater response was seen in sGaw following inhaled treatment (P less than 0.05). These results suggest that beta-2-sympathomimetic drugs should be administered by the inhaled in preference to the oral route.

Administration, Oral↗
PubMed1995

Sympathomimetic effects of paraxanthine and caffeine in humans.

Caffeine is metabolized extensively (on average 80%) to paraxanthine. With regular caffeine consumption, average serum levels of paraxanthine are two thirds those of caffeine. Both caffeine and paraxanthine competitively and nonselectively inhibit adenosine receptors in vitro. To examine the contribution of paraxanthine to the pharmacologic activity of caffeine, we administered to 12 subjects in a crossover design oral caffeine (2 or 4 mg/kg) versus placebo or oral paraxanthine (same dose as caffeine) versus placebo, each after 3 days of methylxanthine abstinence. Both caffeine and paraxanthine significantly increased diastolic blood pressure, plasma epinephrine levels, and free fatty acids. Caffeine and paraxanthine produced a similar magnitude of response at 4 mg/kg; however, caffeine appeared to produce greater responses than paraxanthine at 2 mg/kg. Caffeine and paraxanthine have similar sympathomimetic actions. The activity of paraxanthine needs to be considered in understanding the clinical pharmacology of caffeine, particularly with chronic, repetitive caffeine consumption.

Adult↗
PubMed1983

Effects of injected sympathomimetic amines on plasma catecholamines and circulatory variables in man.

We measured blood pressure, heart rate (HR), and plasma catecholamine responses to a 5-minute infusion of 0.3 mg/kg d-amphetamine (d-A) and to graded bolus injections of tyramine (Tyr) to a similar increment in systolic pressure (BPs), in 9 and 7 healthy people, respectively. Both sympathomimetic agents dramatically increased BPs (mean increases peaking at 39 and 36 mm Hg for d-A and Tyr), associated with increased plasma norepinephrine (NE) (224 and 149 pg/ml) but unassociated with changes in plasma epinephrine or HR. The time course of BPs and NE responses to Tyr was much shorter than to d-A, but the pattern was similar. The results are consistent with the hypotheses that both agents increase BPs via increased synaptic cleft NE, and that circulating plasma NE reflects "spillover" from the cleft into the general circulation.

Blood Pressure↗
PubMed1993

Role of the baroreflex in beta 2-sympathomimetic induced tachycardia in male rats.

The aim of the study was to determine whether tachycardia which is associated with the use of beta 2-sympathomimetic tocolytic agents is caused by baroreflex activation or by direct stimulation of cardiac beta-adrenoceptors. In conscious male rats, tachycardiac responses following intravenous injection of hexoprenaline, ritodrine and fenoterol were compared following (i) bilateral sinoaortic denervation (SAD) or (ii) sham-operation, and (iii) ganglionic-blockade using hexamethonium. Dose-ranges were chosen to result in similar reductions in diastolic blood pressure (DAP). Furthermore, following ganglionic blockade, the relative contribution of beta 1-adrenoceptor stimulation was assessed using the selective beta 2-receptor antagonist ICI 118,551. In intact rats, increases in HR induced by all beta-adrenoceptor agonist were comparable. In SAD and ganglion-blocked rats, DAP fell more pronounced at even lower doses. The corresponding increases in HR were approximately 3 times smaller than in intact rats but not different between agents. During ganglionic blockade ICI 118,551 significantly inhibited HR responses to fenoterol and hexoprenaline but not ritodrine. The conclusion is that in intact male rats, baroreflex activation is the major determinant of tachycardia following injection of ritodrine, fenoterol or hexoprenaline. Increasing the beta 2-selectivity of these drugs will not limit the tachycardic effects.

Adrenergic beta-Agonists↗
PubMed1989

Sympathomimetic amine-induced potentiation of fibrinolytic activity is partly modulated by endogenous prostaglandins in the rat.

Blood fibrinolytic activity was assessed on fibrin plates. Epinephrine and norepinephrine produced a time-dependent potentiation of fibrinolysis following intravenous injection into rats which was reduced by indomethacin (3 mg/kg, i.v.) and completely abolished by phentolamine (0.1 mg/kg, i.v.). Propranolol (0.5 mg/kg) had no effect on the fibrinolysis produced by epinephrine. The study demonstrates that endogenous prostaglandins modulate in part the fibrinolysis induced by sympathomimetic amines via activation of alpha-adrenoceptors in vivo.

Animals↗
PubMed1976

Biochemical actions of sympathomimetic drugs which overcome cycloheximide-induced amnesia.

Earlier investigations of sympathomimetic drugs overcoming the amnesic action of cycloheximide (CXM) in day-old chickens were extended to biochemical studies in vitro. The effects of amphetamine, norepinephrine, alpha and beta noradrenergic stimulants and receptor blockers on Na+/K+ ATP'ase activity in total homogenate of chicken forebrain were investigated. Norepinephrine and the beta stimulant, isoprenaline significantly stimulated the activity of this enzyme, while the beta blocker, propranolol inhibited activity. Amphetamine, the alpha stimulant, methoxamine and the alpha receptor blocker, piperoxane had no effect on Na/K+ ATP'ase activity in total homogenate. In a purified synaptosomal preparation, both amphetamine (5 X 10(-5) M) and norepinephrine (1 X 10(-4) M) produced a slight stimulation of Na+/K+ ATP'ase activity. A similar concentration of amphetamine (1.12 X 10(-4) M) did not inhibit 14C-leucine uptake or incorporation into protein in the synaptosomal fraction. Nor was it able to alleviate CXM inhibition of 14C-leucine incorporation into synaptosomal protein. The results are interpreted in terms of amphetamine (via release of norepinephrine) norepinephrine and isoprenaline stimulating and maintaining the labile, sodium pump-dependent, phase of memory formation for a sufficient length of time until protein synthesis inhibition by CXM wears off.

Adenosine Triphosphatases↗
PubMed1990

Stereoselectivity in beta-adrenomimetic and beta-adrenolytic actions of carteolol, a beta-adrenoceptor blocker with intrinsic sympathomimetic action in guinea-pig taenia caecum.

1. The beta-adrenomimetic and beta-adrenolytic activities of S(-) and R(+) isomers of carteolol, a beta-adrenergic partial agonist (a beta-adrenoceptor blocker with intrinsic sympathomimetic action) were tested in the guinea-pig taenia caecum. 2. The beta-adrenoceptor blocking activities (pA2 values) of S(-) and R(+) isomers of carteolol were significantly larger than the corresponding beta-adrenomimetic activities (pD2 values), supporting our views that beta-adrenoceptors contain two different binding sites; high and low affinity sites. 3. In beta-adrenoceptor blocking action S(-) carteolol was about 10 times as potent as R(+) carteolol while beta-adrenomimetic action of S(-) carteolol was about 2 times as potent as that of R(+) carteolol. Further, intrinsic activity for S(-) carteolol was slightly but significantly larger than that for R(+) carteolol. 4. These results suggest that the binding site for competitive antagonism between S(-) isoprenaline and S(-), R(+) and RS(+/-) carteolol is more stereoselective than the binding site to induce beta-adrenomimetic action.

Adrenergic beta-Agonists↗
PubMed1976

Stress incontinence: conservative therapy with sympathomimetic drugs.

There were 77 women with mild to moderate stress urinary incontinence treated with the sympathomimetic agent, phenylpropanolamine hydrochloride, combined with chlorpheniramine maleate and isopropamide iodide in a sustained release capsule (Ornade). The majority of these patients achieved significant improvement 3 months to 3 years after beginning therapy. A trial of conservative therapy is advisable for stress incontinence, especially when symptoms are mild or when the patients are in a poor risk category. Similar management of post-prostatectomy stress incontinence in men was disappointing. However, the occasional excellent results in patients with mild symptoms appear to justify a trial of conservative therapy before considering operative intervention in this group of patients.

Administration, Oral↗
PubMed1986

The influence of intrinsic sympathomimetic activity and beta-1 receptor selectivity on the recovery of finger skin temperature after finger cooling in normotensive subjects.

A double-blind randomized study was designed to investigate differences in the recovery of finger skin temperature after finger cooling during dosing with placebo or one of four beta-blockers: propranolol, atenolol, pindolol, and acebutolol. In 11 normotensive nonsmoking subjects, finger skin temperature was measured with a thermocouple before and 20 minutes after immersion of one hand in a water bath at 16 degrees C. This finger cooling test caused no significant changes in systemic hemodynamics such as arterial blood pressure, heart rate, and forearm blood flow. The recovery of finger skin temperature during propranolol dosing was better than that during pindolol and atenolol dosing. There were no differences between the recoveries of skin temperature during pindolol, atenolol, and acebutolol dosing. Thus we could demonstrate no favorable effect of intrinsic sympathomimetic activity or beta 1-selectivity on the recovery of finger skin temperature after finger cooling.

Acebutolol↗
PubMed1982

Effects of inhalation of beta-sympathomimetic and atropine-like drugs on airway calibre in normal subjects.

1. Bronchodilatation was produced in eight normal subjects by inhalation, on separate occasions, of the atropine-like drug ipratropium bromide (0.16 mg by pressurized inhaler; 1 mg nebulized) and the beta 2-sympathomimetic salbutamol (0.8 mg by pressurized inhaler; 5 mg nebulized). 2. Mean specific airways conductance (sGaw) increased from a mean value of 0.185 +/- SE 0.002 to 0.292 +/- 0.023 s-1 kPa-1 after ipratropium bromide, and from 0.184 +/- 0.020 to 0.303 +/- 0.026 s-1 kPa-1 after salbutamol. These increases in sGaw were not significantly different from each other. 3. During both maximal and partial expiratory flow volume manoeuvres similar increases in flow rates were produced by each drug, at all lung volumes, from 40 to 20% of vital capacity. 4. Changes in maximal and partial flow volume curves after washout of lung air with helium/oxygen (4:1) were measured before and after each drug. Flow rates increased in all subjects and the percentage increase in maximum flow when helium was breathed was not significantly different, when repeated after each drug. 5. Thus our results suggest that salbutamol and ipratropium have similar sites of action, both affecting both large and small airways, and produce similar degrees of bronchodilatation. This is supported by our results after the helium/oxygen breathing, where the lack of change in density dependence of maximal flow suggests that there was no change in the distribution of airways resistance after the drugs.

Adult↗
PubMed1982

A study of the thermic responses to a meal and to a sympathomimetic drug (ephedrine) in relation to energy balance in man.

1. Sixteen adult male volunteers were selected on the basis of body size and customary food intake: half could be described as "lean' and habitually consuming large amounts of food (group mean +/- SEM: 15.03 +/- 1.13 MJ/d), the high-energy-intake group (HEI group), and half though "lean' admitted to a weight problem and regularly consumed a lower than average food intake (group mean +/- SEM: 6.90 +/- 0.39 MJ/d), the low-energy-intake group (LEI group). 2. Energy expenditure was measured by open-circuit indirect calorimetry. Resting metabolic rate (RMR) was recorded. A meal (Complan, either 2.1 MJ or 4.2 MJ), ephedrine hydrochloride (0.25 mg and 0.50 mg/kg body-weight) or a water control were then administered and metabolic rate (MR) was measured for 4 h. Blood was collected before and 1 h after the meal or drug, and the serum analysed for various hormones and blood metabolites. 3. The size of the thermic response to feeding but not the time-course was related to meal size in both groups. MR increased by 21.6 and 28.6% in the HEI group and by 8.2 and 20.0% in the LEI group in response to the 2.1 and 4.2 MJ Complan meals respectively. Fasting insulin levels were similar in both groups but showed a significantly higher level in the LEI than HEI group after the Complan meals. 4. The mean RMR increased by 5.2 and 10.3% in the LEI in response to ephedrine and by 15.7 and 11.2% in the HEI groups after 0.25 mg and 0.50 mg ephedrine/kg respectively. The rise in serum-free fatty acids in response to ephedrine was significantly higher in the HEI group than in the LEI group. 5. These results suggest (1) the meal size required to promote a maximum thermic effect is smaller in energetically-inefficient individuals (2) the sensitivity to a sympathomimetic drug is also increased in energetically-inefficient individuals. 6. We conclude that in energetically-efficient individuals both the thermic response to a meal and the sympathetic-mediated thermogenesis are lower than in energetically-inefficient ones.

Adult↗
PubMed1983

Haemodynamic consequences of intrinsic sympathomimetic activity and cardioselectivity in beta-blocker therapy for hypertension.

The relevance of intrinsic sympathomimetic activity (ISA) and cardioselectivity for the acute and long-term haemodynamic effects of beta-blocker therapy for hypertension was assessed from reports in the literature. The beta-blockers included in this survey are pindolol, practolol, alprenolol, oxprenolol, acebutolol, penbutolol, metoprolol, atenolol, propranolol and timolol. Forty-four acute and 41 long-term studies in 430 and 482 subjects respectively, were analysed. In acute studies arterial pressure is barely lowered, whereas in spite of the many pharmacological and physicochemical differences beta-blockers appear to have a hypotensive effect of approximately equal magnitude during long-term treatment. In the acute studies, the falls in heart rate, stroke volume, cardiac output and subsequently increased total peripheral resistance are inversely proportional to the pharmacologically defined quantity of ISA of the beta-blockers. The response of vascular resistance to cardiodepression is similar for non-selective and beta 1-selective agents. During long-term therapy, the inverse correlation between cardiac output and vascular resistance is shifted to a lower level of vascular resistance. This reduction of vascular resistance at any level of cardiac output that underlies the hypotensive action of beta-blockers is associated with an increase in stroke volume. Thus, the absolute value of vascular resistance during beta-blocker therapy is determined by the degree of ISA, irrespective of the quality of cardioselectivity. Consequently, beta-blockers with sufficient ISA to prevent disturbance of tissue perfusion at rest reduce the characteristically elevated vascular resistance in longstanding arterial hypertension in contrast with beta-blockers lacking this property. This can have implications for the long-term prognosis of this condition.

Adrenergic beta-Antagonists↗
PubMed1988

Volatile anesthetics attenuate sympathomimetic actions on the guinea pig SA node.

The authors examined and compared the direct effects of three volatile anesthetic agents and three sympathomimetic agonists on transmembrane action potential (AP) characteristics and automaticity of sinoatrial (SA) nodal pacemaker cells. SA nodal tissue was isolated from guinea pig hearts and suffused in vitro with oxygenated Krebs-Ringer solution. Electrophysiologic variables measured were: amplitude of the AP, slopes of phase 4 and of phase 0 of the AP, AP duration, and spontaneous sinus rate. The authors found that 1 and 2 MAC equivalents of each anesthetic, 0.8 and 1.6 vol % halothane, 1.4 and 2.8 vol % isoflurane, and 1.7 and 3.4 vol % enflurane similarly depressed the slopes of phase 4 and 0 of the AP, prolonged AP duration, and slowed the sinus rate at 1 and 2 MAC equivalents. Isoproterenol, 0.25 microM, and epinephrine, 50 microM, maximally enhanced the slopes of phase 4 and 0 of the AP, shortened AP duration, and increased the sinus rate, but phenylephrine, 50 microM, only moderately increased the slope of phase 4 and the sinus rate. Each of the three anesthetics caused baseline depressions of phase 4 and phase 0 slopes and of automaticity of SA nodal cells; the fall in sinus rate was counteracted, but was not reversed maximally by increasing the concentrations of isoproterenol, epinephrine, or phenylephrine. Regression analyses of linearly transformed data showed that each of the anesthetics similarly depressed basal sinus rate, so that changes in rate produced with isoproterenol and epinephrine were not different from those observed with beta agonists in the absence of anesthetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed2003

Responses to sympathomimetics in rat sensory neurones after nerve transection.

Noradrenaline activation of sensory somata that project in damaged peripheral nerves has been postulated to underlie sympathetically-mediated pain. Intracellular recordings from some neurones with myelinated axons in acutely isolated rat dorsal root ganglia showed small prolonged depolarizations to brief applications of 0.1-5 mM noradrenaline whether or not the spinal nerve had been transected. Similar responses were evoked to noradrenaline when phentolamine was present, and also to 1-5 mM catechol, but not 1 mM clonidine, implying the responses were not adrenoceptor-mediated. In extracellular recordings from similar preparations after sciatic transection, many spontaneously active myelinated dorsal root axons were excited by noradrenaline and other sympathomimetics. Silent axons in injured or control ganglia did not respond. Thus, non-specific depolarizations may activate neurones that are hyperexcitable after a lesion but activation of neuronal alpha-adrenoceptors by sympathetically-released noradrenaline seems unlikely.

Action Potentials↗
PubMedDate not supplied

Clinical, electrocardiographic, and hemodynamic effects of ICI 89,406, a new cardioselective beta-adrenoceptor antagonist with intrinsic sympathomimetic activity, in patients with angina pectoris.

ICI 89,406, a new cardioselective beta-adrenoceptor antagonist possessing marked intrinsic sympathomimetic activity, was administered (0.04 mg/kg, i.v.) to 10 patients with stable, uncomplicated, exercise-induced angina pectoris and angiographically proven coronary artery disease. The drug resulted in a significant reduction in heart rate (from 125 +/- 5 to 110 +/- 4/min, p less than 0.001), mean systemic arterial pressure (from 147 +/- 4 to 137 +/- 3 mm Hg, p less than 0.01), and electrocardiographic ST-segment depression (from 1.9 +/- 0.5 to 0.8 +/- 0.3 mm, p less than 0.01) without any change in pulmonary arterial or wedge pressure during submaximal supine leg exercise on a bicycle ergometer. These changes were accompanied by a reduction of cardiac output in 6/10 patients and of the duration of pain in 8/10 patients. At rest, all the hemodynamic parameters remained essentially unchanged in comparison with the control study. These studies indicate that ICI 89,406 produces effective beta-adrenoceptor blockade during exercise in patients with angina pectoris. The partial agonist activity of the drug may be responsible for the minimal circulatory response at rest.

Adrenergic beta-Antagonists↗