tailieunhanh - Drugs and Poisons in Humans - A Handbook of Practical Analysis (Part 39)

Introductio: β-Blockers (β-adrenergic receptor antagonists) block the effects of catecholamines on signal transmission through β-receptors; they cause hypotension by decreasing the heart beat rate and cardiac output, and prevent the attacks of arrhythmia and angina pectoris. In the brain, the drugs attenuate migraine by suppressing the dilation of blood vessels; in the eye, they decrease intraocular pressure by suppressing the production of aqueous humor. Since the drugs are also effective in suppressing muscle quivering and in suppressing overreaction of the thyroid gland upon being too nervous, they are used as doping drugs in competitive sports such as shooting and archery,. | ß-Blockers by Makoto Ueki Introduction p-Blockers p-adrenergic receptor antagonists block the effects of catecholamines on signal transmission through p-receptors they cause hypotension by decreasing the heart beat rate and cardiac output and prevent the attacks of arrhythmia and angina pectoris. In the brain the drugs attenuate migraine by suppressing the dilation of blood vessels in the eye they decrease intraocular pressure by suppressing the production of aqueous humor. Since the drugs are also effective in suppressing muscle quivering and in suppressing overreaction of the thyroid gland upon being too nervous they are used as doping drugs in competitive sports such as shooting and archery which require psychic powers of concentration rather than aerobic performance. As untoward effects of these drugs chill of extremities due to the contraction of vessels and aggravation of bronchial asthma due to contraction of the bronchi can be mentioned. The drugs can be classified into p1- and p2-blockers the p1-receptors are mainly located in the heart muscle while the p2-receptors located in the smooth muscles of the airways and blood vessels. The p1-blockers specifically exert blocking action on the p1-receptors otherwise the p-blockers act on both p1- and p2-receptors. The p-blockers are structurally classified into isopropylamino drugs such as propranolol and tertiary butylamino drugs such as nadolol and many products containing 26 kinds of p-blockers are commercially available in Japan. The metabolism of p-blockers depends upon the hydrophobicity of their side chain structures. The drugs with hydrophilic side chains such as atenolol labetalol and nadolol are excreted into urine in unchanged forms while the drugs with hydrophobic side chains are excreted into urine in the glucuronide-conjugated forms after their hydroxylation. Therefore it is almost difficult to detect unchanged forms of drugs from urine for such hydrophobic p-blockers. The concentration ratio