Adrenergic synapse blockers
These medicinal products disrupt the transmission of nerve impulses. The blockade occurs at the stage of signal transition from the endings of postganglionic sympathetic fibers directly to effector organs.
Classification within this group relies strictly on the localization of the target site:
- Adrenoceptor antagonists. Their target is the postsynaptic membrane. The mechanism involves the direct blockade of adrenergic receptors.
- Sympatholytics. They work at the presynaptic level by acting on the nerve endings themselves. They do not affect receptors, but instead reduce the release of the neurotransmitter norepinephrine into the synaptic cleft.
Gastrointestinal cytoprotectors
The main task of this group is to increase the resistance (stability) of the mucous membrane of the stomach and duodenum to the destructive effects of aggressive factors in gastric juice.
According to the mechanism of protection, two subgroups are distinguished:
- Mucus secretion stimulants. They enhance natural barrier functions. This includes synthetic prostaglandin analogues (Misoprostolum, Enprostilum) and licorice-based preparations (Carbenoxolonum).
- Film-forming agents. They create a reliable mechanical barrier on the mucosal surface. These include Sucralfatum and bismuth preparations (Bismuthi subnitras, Bismuthi tricalii dicitras).
Tocolytics
The special feature of tocolytics is that drugs from completely different pharmacological groups, differing in their mechanism of action, are used in clinical practice to relax the uterus:
- Beta-2 agonists: Hexoprenalinum, Salbutamolum, Terbutalinum, Fenoterolum.
- Progestogens (progesterone preparations): Hydroxyprogesteroni caproas and combination products (Ethinylestradiolum + Acetomepregenolum).
- Oxytocin receptor antagonists: Atosibanum.
- Myotropic antispasmodics: Magnesii sulfas.
- Central nervous system depressants: include general anesthetics (Enfluranum) and anxiolytics (Diazepamum).
Drugs affecting the cardiovascular system
To successfully understand pharmacodynamics, it is necessary to clearly differentiate drugs according to their primary mechanism of action.
- Neurotropic agents. They are divided into centrally acting drugs (Moxonidinum) and peripherally acting drugs (various adrenoceptor antagonists: Doxazosinum, Atenololum, Nebivololum). It is important to remember that Nifedipinum does not belong here.
- RAAS inhibitors (renin-angiotensin-aldosterone system). These include ACE inhibitors (Enalaprilum) and angiotensin II receptor blockers (Losartanum). Notably, beta-blockers (e.g., Propranololum) can also inhibit renin secretion, but they do so indirectly.
- Myotropic agents. These are direct vasodilators and calcium channel blockers. The group includes calcium channel blockers (Amlodipinum), arteriolar vasodilators (Hydralazinum), and mixed-type vasodilators (Nitroprussidum).
Please note: although Doxazosinum (an alpha-blocker) and Losartanum (an ARB) ultimately lead to vasodilation, their primary mechanism of action is completely different, and therefore they are not classified as myotropic agents.
How to remember the difference in adrenergic synapses: Sympatholytics subdue neurotransmitter release (presynapse), while adrenoceptor antagonists attack the receptors themselves (postsynapse).
Class and exam questions
What is the fundamental difference between adrenoceptor antagonists and sympatholytics?
Adrenoceptor antagonists work directly on the postsynaptic membrane, carrying out a direct blockade of receptors. Sympatholytics, on the other hand, act presynaptically, reducing the release of the neurotransmitter norepinephrine from nerve endings.
Does the drug nifedipine belong to the group of neurotropic agents?
No, Nifedipinum is a classic calcium channel blocker. It belongs to myotropic agents that act directly on vascular smooth muscle.
How do beta-blockers affect the renin-angiotensin-aldosterone system?
Drugs of this pharmacological group, for example, Propranololum, do not block the system directly, but are capable of indirectly inhibiting renin secretion, thereby reducing overall RAAS activity.
Through what mechanism do bismuth preparations work in gastroenterology?
They belong to the class of gastrocytoprotectors, which create a reliable protective mechanical film on the surface of the mucous membrane of the stomach and duodenum.
What else to study on this topic
- Mechanisms of action of synthetic prostaglandin analogues.
- Differences between arteriolar and mixed vasodilators.
- Pharmacodynamics of oxytocin receptor antagonists.
- Central and peripheral effects of neurotropic drugs.
- Effect of general anesthetics and anxiolytics on myometrial tone.
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