Drug adrenoceptor antagonist

Class II drugs are classical (3-adrenoceptor antagonists such as propranolol, atenolol, metoprolol or the short-acting substance esmolol. These drugs reduce sinus rate, exert negative inotropic effects and slow atrioventricular conduction. Automaticity, membrane responsiveness and effective refractory period of Purkinje fibres are also reduced. The typical extracardiac side effects are due to (3-adrenoceptor blockade in other organs and include bronchospasm, hypoglycemia, increase in peripheral vascular resistance, depressions, nausea and impotence. 

Class II antiarrhythmic drugs are (3-adrenoceptor antagonists such as propranolol, metoprolol or atenolol. (3-adrenoceptor antagonists slow sinus rate and atrioventricular conduction and exert negative inotropic effects. 

These observations question the role of noradrenaline as an initiator of anxiety as does the finding that the anti-anxiety drug, buspirone (see Chapter 9), increases the concentration of noradrenaline in the extracellular fluid in the frontal cortex of freely-moving rats (Done and Sharp 1994). Whether this is because buspirone is metabolised to l-(2-pyrimidinyl)-piperazine (1-PP), which is an a2-adrenoceptor antagonist, is uncertain. Unfortunately, no studies have investigated the effects of chronic administration of this drug on noradrenergic transmission this could be important because, unlike benzodiazepines, buspirone is effective therapeutically only after several weeks of treatment. 

Hoffman, B.B., Adrenoceptor antagonist drugs, in Basic and Clinical Pharmacology, 8th ed., Katzung, B.G., Ed., Lange Medical Books/McGraw-Hill, New York, 2001, chap. 10. 

Trausch, B., Oertel, R., Richter, K., Gramatte, T., Disposition and bioavailability of the P-adrenoceptor antagonist Talinolol in man, Biopharmaceut. Drug Disp. 1995, 16, 403-414. 

Propranolol An antihypertensive drug the (5)-enantiomer is 130-fold more potent than the (i )-enantiomer, a )3-adrenoceptor antagonist. 

Cardiovascular drugs - digitalis preparations, beta adrenoceptor antagonists, some antiarrhythmic drugs... 

Drugs that antagonize the actions of acetylcholine are known as cholinoreceptor antagonists those that antagonize norepinephrine are known as adrenoceptor antagonists. 

Thus, it seems that the lack of sympathetic nervous system inhibition produced by the vasodilators, which is advantageous in some ways, can also be a disadvantage in that reflex increases in sympathetic nerve activity will lead to hemodynamic changes that reduce the effectiveness of the drugs. Therefore, the vasodilators are generally inadequate as the sole therapy for hypertension. However, many of the factors that limit the usefulness of the vasodilators can be obviated when they are administered in combination with a -adrenoceptor antagonist, such as propranolol, and a diuretic. Propranolol reduces the cardiac stimulation that occurs in response to increases in sympathetic nervous activity, and the... 

The adrenoceptor-blocking agents are described in detail in Chapter 11, although their use in the treatment of hypertension is briefly described here. Drugs of this group are subdivided into a-adrenoceptor antagonists (a-blockers) and (3-adrenoceptor antagonists ((3- blockers). 

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