Blockers of – adrenergic receptors inhibit the effects of – adrenergic stimuli on various organs. Stimulation of the – receptors leads to renin release, vasodilation, bronchodilatation, an increase in cardiac output and pulse; increased insulin secretion, glycogenolysis, gluconeogenesis in the liver and skeletal muscles. – blockers block these effects to varying degrees, depending on the drug and the type of receptor inhibited. For example, they can cause vasoconstriction, bronchoconstriction, a decrease in heart rate, a decrease in cardiac output, a decrease in myocardial oxygen demand, a decrease in blood pressure. Anti-hypertensive effect associated with blockade. – receptors with a subsequent decrease in heart rate and contractility of the myocardium and – receptors with a decrease in coronary or peripheral constriction. The antianginal effect is explained by reducing the energy expenditure of the heart, as well as by redistributing the coronary blood flow of the myocardium in favor of ischemic lesions.
All adrenergic blockers possess more or less equivalent antihypertensive effect and are divided according to the selectivity of action into 1- and 2-adrenoreceptors. Drugs that selectively block – PE receptors, called cardioselective. Others (. Propranolol, timolol, etc.) act simultaneously on 1- and 2 – receptors.
– adrenergic blockers reliably reduce the frequency and duration of “silent” and painful episodes during myocardial ischemia and coronary artery disease, and also improve the prognosis of life due to the additional antiarrhythmic effect.
If the patient also suffers from diabetes mellitus, chronic occlusive peripheral arterial disease or COPD, then it is better to use cardio – selective – blockers (metoprolol, atenolol, betaxolol or acebutolol) . However, cardioselectivity is only relative and decreases with increasing dose of drugs. In severe bronchial asthma or COPD with severe bronchospastic component even contraindicated cardioselective – blockers, since even a small block – comrade agonis- can enhance bronchial asthma. In patients with severe peripheral arterial zabolevani- s, even a partial blockage – receptors leave the − receptors (vasoconstrictors) without counteraction, which contributes to the worsening of the disease. The use of – blockers is contraindicated in Raynaud’s syndrome. With some caution their use in patients with type 1 diabetes, since – blockers reduce insulin secretion, causing deterioration in glucose tolerance, cause disturbances sympaticoadrenal regulation at reducing sugar after injectable insulin tion or physical stress and promote thus the appearance of hypoglycemic states. Influenced by non-selective – blockers for long-term therapy increases the level of free fatty acids and the resynthesis of triglycerides in the liver. At the same time, with such therapy, a decrease in HDL is observed, which is explained by inhibition of lipoprotein lipase and the conversion caused by this change inside the lipoprotein fraction. These negative effects are less inherent carboxy dioselektivnym – blockers.
– blockers with intrinsic sympathomimetic activity (ICA), such as pindolol, penbutolol, cardolol and acebutolol , do not adversely affect serum lipids. Compared with – blockers that do not possess ICA, they are less likely to cause severe bradycardia.
Labetalol – a drug with a combined – and – blocking action – like – blockers with ICA, does not cause a decrease in heart rate to the extent that -blockers without ICA do, and, apparently, does not affect the levels serum lipids.
– blockers that do not have ICA and -blocker properties have a cardioprotective effect in persons who have had a myocardial infarction, and therefore are especially indicated when hypertension develops in them.
In chronic renal failure or impaired renal function, their dosage should be reduced due to renal excretion.
– blockers were recommended as one of the drugs of choice for the treatment of hypertension. Most people tolerate them well, and when used as monotherapy in 40% -50% blood pressure returns to normal. However, in combination with small doses of diuretics, their effectiveness is significantly increased.
The disadvantages of – blockers include a high incidence of side effects from the CNS (sleep disorders, fatigue, drowsiness) and the presence of contraindications (atrioventricular block of the second degree and above, bronchial asthma, sick sinus syndrome, heart failure).