Isoprenaline Health Dictionary

The sites in the body on which ADRENALINE and comparable stimulants of the SYMPATHETIC NERVOUS SYSTEM act. Drugs which have an adrenaline-like action are described as being adrenergic. There are ?ve di?erent types of adrenergic receptors, known as alpha1, alpha2, beta1, beta2 and beta3 respectively. Stimulation of alpha receptors leads to constriction of the bronchi, constriction of the blood vessels with consequent rise in blood pressure, and dilatation of the pupils of the eyes. Stimulation of beta1 receptors quickens the rate and output of the heart, while stimulation of beta2 receptors dilates the bronchi. Beta3 receptors are now known to mediate so-called non-shivering thermogenesis, a way of producing heat from specialised fat cells that is particularly relevant to the human infant.

For long it had been realised that in certain cases of ASTHMA, adrenaline had not the usual bene?cial e?ect of dilating the bronchi during an attack; rather it made the asthma worse. This was due to its acting on both the alpha and beta adrenergic receptors. A derivative, isoprenaline, was therefore produced which acted only on the beta receptors. This had an excellent e?ect in dilating the bronchi, but unfortunately also affected the heart, speeding it up and increasing its output – an undesirable e?ect which meant that isoprenaline had to be used with great care. In due course drugs were produced, such as salbutamol, which act predominantly on the beta2 adrenergic receptors in the bronchi and have relatively little e?ect on the heart.

The converse of this story was the search for what became known as BETA-ADRENOCEPTORBLOCKING DRUGS, or beta-adrenergic-blocking drugs. The theoretical argument was that if such drugs could be synthesised, they could be of value in taking the strain o? the heart – for example: stress ? stimulation of the output of adrenaline ? stimulation of the heart ? increased work for the heart. A drug that could prevent this train of events would be of value, for example in the treatment of ANGINA PECTORIS. Now there is a series of beta-adrenoceptor-blocking drugs of use not only in angina pectoris, but also in various other heart conditions such as disorders of rhythm, as well as high blood pressure. They are also proving valuable in the treatment of anxiety states by preventing disturbing features such as palpitations. Some are useful in the treatment of migraine.... adrenergic receptors

Substances that can be inhaled into the body through the lungs. They may be delivered in traditional form dissolved in hot water and inhaled in the steam, or as an aerosol – a suspension of very small liquid or solid particles in the air. The latter are now usually delivered by devices in which the aerosol is kept under pressure in a small hand-held cylinder and delivered in required doses by a release mechanism.

Aerosols Asthmatic patients (see ASTHMA) ?nd aerosol devices to be of value in controlling their attacks. They provide an e?ective and convenient way of applying drugs directly to the bronchi, thus reducing the risks of unwanted effects accompanying SYSTEMIC therapy. BRONCHODILATOR aerosols contain either a beta-sympathomimetic agent or ipratropium bromide, which is an ANTICHOLINERGIC drug.

ISOPRENALINE was the ?rst compound to be widely used as an aerosol. It did however stimulate beta1 receptors in the heart as well as beta2 receptors in the bronchi, and so produced palpitations and even dangerous cardiac arrhythmias. Newer beta-adrenoceptor agonists are speci?c for the beta2 receptors and thus have a greater safety margin. They include SALBUTAMOL, TERBUTALINE, rimiterol, fenoterol and reproterol. Unwanted effects such as palpitations, tremor and restlessness are uncommon with these, more speci?c preparations. In patients who get insu?cient relief from the beta-adrenoreceptor agonist, the drug ipratropium bromide is worth adding. Salmeterol is a longer-acting choice for twice-daily administration: it is not intended for the relief of acute attacks, for which shorter-acting beta2 stimulants such as salbutamol should be used. Salmeterol should be added to existing corticosteroid therapy (see CORTICOSTEROIDS), rather than replacing it.

Patients must be taught carefully and observed while using their inhalers. It is important for them to realise that if the aerosol no longer gives more than slight transient relief, they should not increase the dose but seek medical help.... inhalants

These drugs stimulate the activity of the SYMPATHETIC NERVOUS SYSTEM. There are three groups: inotropic and vasoconstrictor sympathomimetics, and those used for cardiopulmonary resuscitation. The properties of these drugs vary according to whether they act on alpha or beta adrenergic receptors.

Inotropics act on beta receptors in heart muscle (see HEART), increasing its contractility and sometimes the heart rate. DOBUTAMINE and DOPAMINE are cardiac stimulants, while dopexamine acts on heart muscle and, via peripheral dopamine receptors, increases the excretion of URINE. ISOPRENALINE is used only as emergency treatment of heart block (interruption of the heart’s conduction) or severe slowing of the heart rate (bradycardia).... sympathomimetic drugs

A common disorder of the heartbeat caused by an interruption to the passage of impulses through the heart’s conducting system.

There are several grades of heart block, from a slight delay between the contractions of the atria (see atrium) and ventricles (called a prolonged P-R interval) to complete heart block, in which the atria and ventricles beat independently. Heart block may be due to coronary artery disease, myocarditis, overdose of a digitalis drug, or rheumatic fever. A prolonged P-R interval causes no symptoms. In more severe heart block, the rate of ventricular contraction does not increase in response to exercise. This may cause breathlessness as a result of heart failure, or chest pains or fainting due to angina pectoris. If the ventricular beat becomes very slow, or if it stops altogether for a few seconds, loss of consciousness and seizure may occur due to insufficient blood reaching the brain. If the delay is prolonged, a stroke may result.Symptomless heart block may not need treatment. Heart block that is causing symptoms is usually treated by the fitting of an artificial pacemaker. Drugs, such as isoprenaline, that increase the heart-rate and the strength of the heart’s contractions, may be given as a temporary measure.... heart block