Никотин сезувчан холинорецепторларга таъсир килувчи воситалар theme of lecture: “n-cholinomimetics. N-cholinoblockers”

Никотин сезувчан холинорецепторларга таъсир килувчи воситалар

THEME OF LECTURE: “N-CHOLINOMIMETICS. N-CHOLINOBLOCKERS”

• Nicotinic cholinoceptors (N-cholinoceptors) have various localizations. They take part in the transmission of efferent impulses in the autonomic ganglia, adrenal medulla, and neuromuscular synapses, in chemoreception and generation of afferent impulses in the carotid body, as well as in interneuronal transmission in the CNS.

N-cholinomimetics

• This group includes such alkaloids as nicotine, lobeline and cytisine. They have a two-phase action on N-cholinoceptors (excitatory stage is alternated with inhibitory effect).
• Nicotine is an alkaloid of tobacco leaves. It does not have any therapeutic value. It is used in experimental pharmacology.
• Nicotine affects both peripheral and central N-cholinoceptors. N-cholinoceptors of the autonomic ganglia, on which nicotine has a two-phase effect, are especially sensitive to it. The first phase (excitation) is characterized by a depolarization of the ganglionic neu­ronal membranes, the second one (inhibition), are provided by competitive antagonism with acetylcholine. Nicotine does not affect the release and hydrolysis of acetylcholine.

• N-cholinomimetics such as lobeline and cytisine are sometimes used in clinical practice as respiratory stimulants of reflex action.
• Both drugs are sometimes administered to stimulate respiration (if reflex excitation of the respiratory center is preserved). It is injected intravenously. Their action is very short-term. Moreover, both alkaloids are used as basic components of a number of drugs, used to aid 'quitting' smoking (cytisine is contained in «Tabex» tablets, lobeline — in «Lobesilum» tablets).

N-cholinoblockers

• This group includes ganglionic blockers, blockers of neuromuscular synapses and some central cholinoblockers.

Ganglionic blockers

• Ganglionic blockers block sympathetic and parasympathetic ganglia, as well as N-cholinoceptors of the adrenal medulla and carotid body.
• Chemically ganglionic blockers can be divided into the following.
• - Bis-quaternary ammonium compounds
• v Benzohexonium
• v Azamethonium (Pentaminum)
• v Trepirium (Hygronium)
• - Tertiary amines
• v Pempidine
• v Pachycarpinum

• There are two groups of drugs. Some of them are intended for long-term administration. The main requirements for such drugs are as follows. They have to have high activity after different routes of administration, long duration of action, low toxicity and absence of any serious side effects. It is important that addiction to these drugs would develop as slowly as possible or not develop at all.
• Ganglionic blockers are used for the treatment of obliterating endarteritis, pulmonary edema, and arterial embolism but seldom for hypertension (mainly in hypertensive emergencies).
• Ganglionic blockers of short-term action are used for controlled hypotension.
• Besides, administration of ganglionic blockers prevents the development of negative reflexes on the heart, vessels and other visceral organs, which can take place during surgical interventions.