Drugs blocking adrenoreceptors

the mediator and catecholamines that circulate in the blood and

other adrenomimetics.
Sympatholytics – drugs inhibiting the transmission of mediators from adrenergic fiber terminals: Adelphan (Reserpine + Dihydralazine + hydrochlorothiazide)

Prazosin, Doxazosin, Tamsulosin
Selective α2 - Yohimbine

and causes pooling of blood in capacitance vessels → venous

return and cardiac output are reduced → fall in BP.
Reflex tachycardia occurs due to fall in mean arterial pressure and increased release of NA due to blockade of presynaptic α2 receptors.

in nasal blood vessels and in radial muscles of iris.
Intestinal

motility is increased.
Tone of smooth muscle in bladder trigone, sphincter and prostate is reduced by blockade of α1 receptors (mostly of the α1A subtype) → urine flow in patients with benign hypertrophy of prostate (BHP) is improved.

blocker for diagnosis and intraoperative management of pheochromocytoma, disorders of

peripheral blood circulation (endarteritis, Raynauld’s disease), hemorragic or cardiogenic shock with spasm of arteriols, hypertensive crises.
Pheochromocytoma (tumor of the adrenal medulla) produces large amounts of epinephrine, which leads to substanial increase of the arterial pressure.

α₂-AR; orthostatic collapse, dizziness, exacerbation of peptic ulcer, dyspepsia, itching,

skin hyperemia. edema, allergic reactions.

alpha-blockers
α-adrenoblocker

Indications for the use:
disorders of cerebral circulation (atherosclerosis of

cerebral vessels, post-stroke conditions, diabetic retinopathy, dystrophic eye diseases), migraine,
acute and chronic peripheral vascular disorders (endarteritis, trophic wounds and ulcers, bedsores).
Side effects: marked decrease in blood pressure, dizziness, dyspeptic disorders (nausea, diarrhea, abdominal pain), a feeling of heat, allergic reactions, drowsiness or insomnia.

vessels, lowers blood pressure, dilates veins, decreases venous return of

blood to the heart, declines preload of the heart; reduces platelet aggregation, reduces the content of atherogenic lipoproteins in the blood.
Prazosin is effective orally. Effect of a single dose lasts for 6–8 hours.
Indications: hypertension and hypertensive crisis, chronic heart failure

are used for the treatment of hypertensive disease, benign hypertrophy

of prostate.
They block α1 receptors in bladder trigone and prostatic smooth muscle, there by improve urine flow, reduce residual urine in bladder.

BHP symptoms, because α1A subtype predominate in the bladder base

and prostate.
Side effects: the effect of the first dose, tolerance, swelling, dizziness, ejaculation disorder, headache, palpitation.

with intrinsic sympathomimetic activity: Pindolol
2. Selective β1 -AB:

Metoprolol, Bisoprolol, Nebivolol
with intrinsic sympathomimetic activity: Acebutolol
3. α and β blockers: Carvedilol, Labetalol

inhibits atrioventricular conduction. The effects become prominent under sympathetic overactivity

(exercise, emotion).
Cardiac work and oxygen consumption are reduced. Total coronary flow is reduced (blockade of dilator β receptors) in the subepicardial region, while perfusion of the subendocardial area (which is the site of ischaemia in angina patients) is not affected.

and conductivity of the atrioventricular node, conductivity in Purkinje fibers,

eliminates the influence of the sympathetic system on the heart, has a weak direct membrane-stimulating effect.
So, rate of diastolic depolarization in ectopic foci is reduced.

cardiac rate and intensity, decreases stroke and minute heart volume,

and decreases systolic blood pressure.
Diastolic pressure firstly increased, but P. blocks βAR of juxtaglomerular apparatus of the kidneys and decreases renin secretion. P. blocks presynaptic vascular β-AR and reduces release of the mediator.
P. inhibits the Central links of the vasoconstrictor reflex.

β-AB
β-adrenoblocker

tachycardia in mitral stenosis, thyrotoxicosis.

tone (numbness of limbs, cold hands and feet),
increased hypoglycemia

in patients with diabetes mellitus, increased blood levels of atherogenic lipoproteins,
drowsiness, lethargy, reduced reactions rate,
edema, dyspepsia, increasing the tone of the uterus

prevent the activating effect of the Central nervous system on

the cardiovascular system. They can be used for fear of public speaking, at stress.
Propranolol inhibits adrenergically provoked tremor.
Propranolol and some other β blockers reduces secretion of aqueous humor; intraocular pressure is lowered.

bronchial (β2) receptors. However, selectivity is only relative and is

lost at high doses.
Their features are:
Lower propensity to cause bronchoconstriction,
Less interference with carbohydrate metabolism and less inhibition of glycogenolysis during hypoglycaemia—safer in diabetics.
Lower incidence of cold hands and feet, Raynaud’s phenomenon.
No/less deleterious effect on blood lipid profile.

β1 and/or β2 receptors submaximally.
The benefits of this property:

Bradycardia and depression of contractility at rest are not prominent, but exercise tachycardia is blocked.
They can be used in elderly patients, with sick sinus.

metabolism, pass through the BBB
Lipo / hydrophilic (bisoprolol, nebivolol, carvedilol)

are eliminated by kidneys and liver.
Hydrophilic (atenolol) are not metabolized in the liver, excreted mainly by the kidneys.

as a NO donor, produces vasodilatation and improves endothelial function,

which may delay atherosclerosis.
It has not effect on plasma lipids and on carbohydrate metabolism.
In contrast to older β blockers, hypotensive response to nebivolol has a rapid onset. It is used in hypertension and CHF.

It reduces the work of the heart, dilates blood vessels,

reduces the secretion of renin, reduces preload and postload of the heart.
It is used in hypertension, coronary artery disease, chronic heart failure.
Side effects: headache, bronchospasm, allergic reactions.
It is used 1-2 times a day.

the process of norepinephrine storage in the vesicles, which leads

to a reduction in its concentration in the varicosities. The main part of mediator is deaminated.
The drug lowers norepinephrine concentrations in the heart, vessels, adrenal medulla, CNS. It inhibits CNS and has calming effect, promotes the developing of sleep.

effect is observed after several days. The drug reduces cardiac

output and decreases peripheral vascular resistance and pressor reflex.
It can cause bradycardia, bronchospasm, an increase in the secretory and motor activity of the gastrointestinal tract and miosis, drowsiness, weakness, depression, extrapyramidal disorders, increase in appetite.
In the treatment of hypertension reserpine is prescribed together with vasodilators and diuretics to enhance the therapeutic effect and reduce side effects.

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