Methyldopa is an a-methoxylated derivative of levodopa that exhibits hypotensive action by reducing overall peripheral vascular resistance and reducing heart work. Antihypertensive action of methyldopa consists of the biotransformation of methyldopa into methylnoradrenaline (methylnorepinephrine), which acts as a "pseudo neurotransmitter." The current, universally accepted point of view is that the action of methyldopa is carried out through the CNS, where methylnorepinephrine, a powerful stimulant of a-adrenergic receptors of the medulla, inhibits the vasomotor center.
It is prescribed for arterial hypertension and hypertensive crises. Synonyms of this drug are aldomet, dopegit, mopatil, and others.
22.4 PERIPHERALLY ACTING SYMPATHOLYTICS (a-ADRENOBLOCKERS)
As was already mentioned (Chapter 12), the characteristic uniqueness of a-adrenoblock-ers is their ability to reduce the pressor effect of adrenaline (epinephrine). In particular, postsynaptic arblockers act on a-receptive regions located on vascular smooth musculature and counteract the pressor, vasoconstricting effect of adrenaline (epinephrine) and noradrenaline (norepinephrine). In addition, they exhibit a direct relaxant effect on the smooth musculature, which leads to peripheral dilation of vessels, and as a result, leads to lower blood pressure. Dilation of peripheral vessels is probably the most important effect of a-adrenoblockers. However, they also exhibit a cardiostimulatory effect, which often becomes the reason for tachycardia. Attempts to treat hypertension with drugs such as phentolamine (12.2.1) and phenoxibenzamine (12.2.6), which block a-adrenergic receptors, have been unsuccessful because of a large number of hindering side effects, and also because of the possibility of developing tolerance to them.
However, a number of a1-selective adrenoblockers and adrenergic neuron blockers are used to treat hypertension.
22.4.1 Reversible competitive ^-selective adrenoblockers
Drugs with a-adrenergic blocking activity are peripheral coronary-dilating agents that only differ in specificity with a1-adrenergic receptors. Prazozin and tetrazin are selective a1-adrenoblockers that are used in therapeutic doses to lower arterial pressure.
Prazosin (12.2.12): Its synthesis is described in Chapter 12.
Prazosin is used to treat average or moderate hypertension. Upon taking this drug, blood pressure drops without substantial changes in indicators of heart work, such as rate, coronary flow, and cardiac output.
Prazosin is used for weak to moderate hypertension. Synonyms of this drug are minipress and minizide.
Terazosin (12.2.13): Its synthesis is described in Chapter 12.
Terazosin is used for the same indications as prazosin; however, it has the advantage of being able to be taken once per day. Synonyms of this drug are heitrin and vasocard.
Adrenergic neuron blockers cause a release of biogenic amines at neuron terminals. These drugs can interfere in the synthesis, storage, and release of norepinephrine, dopamine, and serotonin.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...