Beta blockers receptor antagonist

Compounds which act as antagonists at the receptors for beta sympathetic transmitters (beta blockers) have gained very wide acceptance as antihypertensive agents. It was found subsequent to their introduction that there are two populations of beta receptors the beta-1 receptors are richest in the cardiovascular system whereas beta-2 receptors are mostly found in the bronchi. Lack of receptor-type specificity led to bronchial spasm in some asthmatic individuals on ingestion of the earlier beta blockers. Much of the work outlined below had as its goal the preparation of agents which showed selectivity for beta-1 receptors. 

ACE-I, angiotensin-converting enzyme inhibitor Aid Ant, aldosterone antagonist ARB, angiotensin receptor blocker BB, beta-blocker CCBA, calcium channel blocking agent DirVaso, direct vasodilator. 

Pronounced bradycardia with a beta blocker pronounced hypotension with an angiotensin II receptor antagonist... 

As it inhibits microsomal cytochrome P450 cimetidine has a high potential for drug interactions not shared by the other H2 receptor antagonists. The oxidative metabolism of agents such as anticoagulants, most antiepileptics, some beta-blockers, warfarin, theophylline and many hypnotics, neuroleptics and antidepressants may be reduced, leading to increased effects. 

Beta antagonists are generally administered for their effect on the beta-1 receptors that are located on the heart.31 When stimulated, these receptors mediate an increase in cardiac contractility and rate of contraction. By blocking these receptors, beta antagonists reduce the rate and force of myocardial contractions. Consequently, beta antagonists are frequently used to decrease cardiac workload in conditions such as hypertension and certain types of angina pectoris. Beta blockers may also be used to normalize heart rate in certain forms of cardiac arrhythmias. Specific clinical applications of individual beta blockers are summarized in Table 20-2. 

When nonselective beta blockers are used, some antagonism of beta-2 receptors also occurs.2,31 The antagonism of beta-2 receptors on bronchiole smooth muscle often leads to some degree of bronchoconstric-tion and an increase in airway resistance. Although this event is usually not a problem in individuals with normal pulmonary function, patients with respiratory problems such as asthma, bronchitis, and emphysema may be adversely affected by nonselective beta antagonists. In these patients, one of the beta-1-selective drugs should be administered. 

Alpha-adrenergic antagonists are used primarily as antihypertensive drugs because of their ability to block vascular alpha-1 receptors. Beta-adrenergic antagonists (beta blockers) are administered primarily for their inhibitory effects on myocardial function and are used in the prevention and treatment of hypertension, angina pectoris, arrhythmias, and myocardial reinfarction. Many of the drugs introduced in this chapter are discussed further in chapters that deal with the specific clinical conditions (e.g., hypertension, asthma, and other disorders). 

Beta blockers that bind to both beta-1 and beta-2 receptors (nonselective agents, see Table 20-2) may induce bronchoconstriction in patients with asthma or similar respiratory problems. These patients should be given one of the more cardioselective beta antagonists, such as atenolol (Tenormin) or metoprolol (Lopressor, others). Beta blockers may also produce excessive cardiac depression in individuals with certain types of cardiac disease. Beta blockers are generally well tolerated in most patients, however, and major problems are infrequent. 

The pharmacological treatment options for ACS include agents that either reduce oxygen demand (beta blockers) or increase oxygen supply (nitrates, potassium channel activators, calcium channel blockers) to the heart and antiplatelet (aspirin, ADP-receptor antagonists, GPIIb/llla receptor blockers) and antithrombin therapy (unfractionated heparin, low molecular weight heparin, direct thrombin inhibitors) (10). 

ACE INHIBITORS, ANGIOTENSIN II RECEPTOR ANTAGONISTS, CENTRALLY ACTING ANTIHYPERTENSIVES, VASODILATOR ANTIHYPERTENSIVES BETA-BLOCKERS t hypotensive effect Additive hypotensive effect may be used therapeutically Monitor BP at least weekly until stable. Warn patients to report symptoms of hypotension (light-headedness, dizziness on standing, etc.)... 

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