31 topics with brief reviews: definitions, key facts, and seminar questions.
This section is dedicated to drugs that regulate the tone of the sympathetic nervous system. Here, we analyze in detail the mechanisms of stimulation and blockade of alpha- and beta-adrenoreceptors, as well as the effects of these processes on the cardiovascular system and bronchi.
The material covers the entire spectrum of adrenergic agents. You will find information on direct and indirect adrenomimetics (adrenaline, noradrenaline, ephedrine, phenylephrine, dobutamine) and a wide group of adrenoblockers. The reference guide details non-selective and cardioselective beta-blockers (ranging from propranolol to bisoprolol and nebivolol), alpha-blockers, hydrogenated ergot alkaloids, as well as sympatholytics like guanethidine and central alpha-2-adrenomimetics (clonidine).
During colloquiums and exams, instructors are strictest about the comparative characteristics of beta-adrenoblockers. You need to clearly understand the difference between cardioselective and non-selective drugs, know the indications for carvedilol, and be able to explain the essence of intrinsic sympathomimetic activity. Pay special attention to the pharmacology of these groups in hypertension and heart failure.
What is the difference between adrenomimetics and sympathomimetics?
Adrenomimetics act directly on adrenoreceptors, replacing the natural neurotransmitter. Sympathomimetics do not touch the receptors, but cause the neuron to accumulate or release more of its own noradrenaline.
Why does phenylephrine not cause accommodation paralysis?
Its chemical structure has only one hydroxyl group, so the COMT enzyme cannot inactivate it.
How do α2-mimetics act at the synaptic level?
On the presynaptic membrane, they work via a negative feedback mechanism: they hyperpolarize the membrane and block calcium influx, thereby reducing noradrenaline release.
Why are dobutamine and dopamine not prescribed in tablets?
Both drugs are rapidly degraded by enzymes in the gastrointestinal tract and liver during first-pass metabolism, which is why they are effective only via intravenous infusion.
Why is salmeterol not used to relieve an acute asthma attack?
Due to its extremely high lipophilicity, the molecule becomes firmly "trapped" in the lipid layer of the cell membrane. Its rate of diffusion to the receptor is low, so the bronchodilator effect occurs only after 30 minutes, which is unacceptable in emergency care.
What is the mechanism of action of isoprenaline?
Isoprenaline is a direct non-selective $\beta$-adrenoreceptor agonist. It equally stimulates both $\beta_1$ and $\beta_2$ adrenergic receptors.
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