Cholinomimetics are drugs that increase arousal in the area of the ends of the cholinergic nerve.
Classification
Cholinergic drugs are divided into direct cholinomimetics, which cause the excitation of cholinergic receptors, and anticholinesterase indirect elements that inactivate cholinesterase. The direct type is usually further divided into M- and H-cholinomimetics in pharmacology.
M-cholinomimetics are able to excite predominantly central interneuronal synapses or peripheral neuro-effector regions of the executive organs. In them, the content of M-cholinergic receptors is observed. These include "Pilocarpine" and "Aceclidine."
H-cholinomimetics are drugs that cause the excitation of H-cholinergic receptors. They are considered innervated neurons. Moreover, their bodies are located in the central nervous system, and in addition, in the sympathetic and parasympathetic nodes. They are also found in the medulla of the adrenal glands and in the area of the carotid glomerulus. These include Cititon along with Lobelin. M- and H-cholinomimetics that excite cholinergic receptors include Carbacholine.
The use of cholinomimetics will be considered in this article.
Operating principle
Anticholinesterase drugs block absolutely all active catalytic regions of acetylcholinesterase. Similar processes lead to the accumulation of acetylcholine in the region of the synaptic cleft. As part of the classification of processes according to the mechanism of influence, there is a division into such groups as irreversible and circulating influence.
With the introduction of the direct type of cholinomimetics, the effects associated with excitation of parasympathetic type nerves can significantly prevail in the body. For example, this will be expressed as a slowdown in heart rate, a decrease in the intensity of heart contractions.
Changes
In addition, the following changes occur:
- Intraocular pressure decreases.
- Spasms of accommodation occur.
- The pupils are narrowed.
- Intestinal motility increases.
- The tone of all internal organs increases, especially the condition of smooth muscles.
- Urination increases.
- The vessels expand.
- There is a decrease in blood pressure along with relaxation of the sphincters.
Thus, they are agents that accelerate the mechanism of action of cholinergic nerves.
Cholinomimetics are substances that mimic the effects of acetylcholine and exert an effect similar to irritation of cholinergic nerves on the work of an organ. Some cholinomimetic agents, for example nicotinomimetic substances, can affect mainly cholinergic receptors sensitive to nicotine. The following components should be attributed to them: nicotine, anabazine, lobelia, cytisine and subecholine. As for the muscarinic-sensitive cholinergic receptors, they are affected by substances such as muscarine, arecolin, pilocarpine, benzamon, aceclidine and carbacholine. The effects of cholinomimetics are unique.
Their mechanism of action is identical to the mechanism of acetylcholine, which is released at the ends of cholinergic nerves. It can also be entered externally. Like acetylcholine, these agents have a positively charged nitrogen atom in their molecule.
We consider the mechanism of action of cholinomimetics in more detail for each type.
N-cholinomimetics
N-cholinomimetics are substances that stimulate n-cholinergic receptors. Such elements are also called nicotine sensitive receptors. N-cholinergic receptors are associated with channels of cell membranes. With the excitation of H-cholinergic receptors, the channels open and the membrane enters the depolarization, which causes an energy effect. Cholinomimetics in pharmacology have been used since ancient times.
N-cholinergic receptors predominate in the neurons of the parasympathetic and sympathetic ganglia, as well as in the chromaffin cells of the brain component of the adrenal glands and in the region of carotid tangles. In addition, N-cholinergic receptors can be found in the central nervous system, especially in cells that inhibit spinal cord motor neurons.
N-cholinergic receptors are localized in the neuromuscular synapses, that is, in the region of the terminal plates of skeletal muscles. If stimulated, skeletal structures may contract.
M-cholinomimetics
We consider the drugs below. M-cholinomimetic substances can enhance the secretion of sweat, digestive, and bronchial glands. In addition, due to their effect, the following reactions of the body are observed:
- There is a slowdown in heart rate.
- The vessels expand.
- Blood pressure decreases.
- Smooth muscles of the digestive system, as well as the bronchi, are reduced.
- Smooth muscles of the urinary and biliary ducts are reduced.
- The pupils narrow and a spasm of accommodation is caused.
It is worth noting that M-cholinomimetic agents are mainly used for the treatment of glaucoma. The constriction of the pupils, which is caused by these components, leads to a decrease in intraocular pressure. What is the mechanism of cholinomimetics?
The effects of substances that excite M- and H-cholinergic receptors are mainly similar to the effects of M-cholinomimetic drugs. This is due to the excitation of H-cholinergic receptors. Among the substances that belong to M- and H-cholinomimetics, exclusively anticholinesterase agents find wide therapeutic use.
The mechanism of action of M-cholinomimetics is of interest to many.
Drug poisoning
Poisoning with these agents may be accompanied by the following reactions of the body:
- There is a sharp increase in the secretion of saliva, as well as sweat.
- Diarrhea.
- Narrowing of the pupils.
- Slow heart rate. It should be noted that in case of poisoning with anticholinesterase drugs, the pulse, on the contrary, becomes faster.
- Drop in blood pressure.
- Asthmatic breathing.
Treatment of poisoning in this situation should be reduced to the fact that the patient is administered "Atropine" or other anticholinergic drugs.
Application
Cholinomimetics are substances that excite cholinergic receptors. They are usually used in ophthalmic medicine as a miotic agent that can lower intraocular pressure. In the framework of this, tertiary amines, which are well absorbed by the conjunctiva, are predominantly used, in particular, such drugs as Pilocarpine and Aceclidine.
How to explain the narrowing of the pupils
The narrowing of the pupils under the influence of M-cholinomimetics can be explained by the contraction of the circular muscles of the iris, which receives the cholinergic innervation provided by the oculomotor nerve. This circular muscle contains M-cholinergic receptors. In parallel, due to the process of contraction of the ciliary muscle, which has a similar innervation, accommodation spasms occur, that is, the installation on the near vision of the lens curvature.
Lowering intraocular pressure
Along with the narrowing of the pupil, M-cholinomimetics, as part of their effect on the eye, can cause another very important clinical effect, namely, a decrease in intraocular pressure. It is this process that is used to treat glaucoma.
A similar effect can be explained by the fact that during the narrowing of the pupil the iris thickens, due to which there is an expansion of the lymphatic gaps located in the corner of the anterior chamber of the visual organ. Due to this, there is an increase in the outflow of fluid from the inner regions of the eye, which, in fact, causes a decrease in intraocular pressure. True, such a mechanism is not considered the only reason for the decrease in intraocular pressure caused by M-cholinomimetics, due to the fact that there is no strict correlation between the miotic effects provoked by them and the decrease in intraocular pressure.
Miotic effect
The miotic effect of M-cholinomimetics, provided that they are alternated with mydriatic preparations, can also be used to tear apart adhesions that prevent the regulation of pupil width. The resorptive effect of substances that excite M-cholinergic receptors is used for atony of the intestine and bladder.
In order to avoid the vain process of exciting the ganglia, it is preferable to selectively use active M-cholinomimetics, such as Mecholine or Betanehol. They are administered subcutaneously in order to provide a quick effect, as well as the accuracy of the dosage. Given that this pathway is not associated with absorption through the mucosa, quaternary amine solutions are injected subcutaneously, among which are Karbacholin, Mecholine, or Betanehol. The action of cholinomimetics is not fully understood.
Cholinergic blocking components and their use
Substances that block M-cholinergic receptors have a wider therapeutic use compared to M-cholinomimetics. In the clinic of diseases of the visual organs, selectively affecting M-anticholinergics are used to dilate the pupils, which causes relaxation of the circular muscles of the iris. They are also used to paralyze accommodation of a temporary nature, within which the ciliary muscles are relaxed. Most often, Atropine solution in the form of eye drops is used for such purposes. Cholinomimetic drugs are presented below.
The relaxation of the circular and ciliary muscles of the iris creates a complete rest of the intraocular state, which is used for inflammatory processes, and in addition, for eye injuries. The expansion of the pupils caused by M-anticholinergics along with accommodation paralysis is also used in the study of the refractive function of the lens. For these purposes, instead of Atropine, they prefer to use short-acting M-anticholinergics, usually they are drugs such as Amizil, Gomatropin, Euphthalmin and Metamizil. Their solutions are prescribed in the form of eye drops.
Where is Atropine used?
The main purpose for the resorptive use of selective M-anticholinergics are spasms of smooth muscle organs. Such organs are the stomach, intestines, bile ducts and the like. To do this, directly use Atropine, as well as plants that contain it, for example, belladonna and others. In addition, numerous synthetic M-anticholinergics may be suitable.
An important basis for the use of M-anticholinergics is their central effect. Selective M-anticholinergics with a central effect include drugs such as Amisil, Benzacin, Metamisil and other amino alcohol esters that contain tertiary nitrogen along with aromatic acids, including hydroxyl. As part of blocking the central M-cholinergic receptors, they potentiate the effects of sleeping pills, as well as narcotic and analgesic drugs, preventing the overexcitation of the hypothalamic centers that control the pituitary-adrenal system.
Conclusion
Thus, cholinomimetic agents are substances that can excite cholinergic receptors, that is, biochemical systems of the body. They cannot be homogeneous. They are selectively sensitive to nicotine and are located in the ganglia of the sympathetic, and, in addition, parasympathetic nerves. They can also be observed in the adrenal medulla along with carotid tangles and at the ends of the motor elements of the central nervous system. Cholinergic receptors may also show selective sensitivity to muscarine alkaloid.
We considered the classification of cholinomimetics.