Epinephrine, and endogenic catecholamine, is better known by its official English name adrenaline. Epinephrine is a powerful agonist of both a- and /¡-adrenergic receptors. Its action is very complex and depends not only on the relative distribution of adrenergic receptors in regions of various tissues and organs, but also on the dosage and method of introduction. The natural isomer of epinephrine (—) is 50 times more active than the (+) isomer. It directly and nonspecifically activates both a- and /¡-adrenergic receptors. Activation of a-adrenoreceptors leads to constriction of most blood vessels. Activation of ¡1-adrenoreceptors increases the heart rate and strength of contractions of cardiac muscle. Activation of /¡2-adrenoreceptors leads to a dilation of bronchi and skeletal muscle blood vessels. The level of blood glucose increases, and intraocular pressure also increases. Despite the fact that the primary pharmacological action is reflected on the cardiovascular and respiratory systems, the complete spectrum of its effects shows its physiological significance as a systemic neurohormone involved in the activation of a large number of protective functions.
As a matter of fact, it is a prototype of many adrenergic drugs, and therefore its action on individual organ systems should be examined more carefully. A typical reaction upon intravenous introduction of epinephrine is the dramatic increase mainly in systolic blood pressure. A similar effect of epinephrine results from a combined action: first, contraction of the majority of blood vessels, and second, stimulation of the myocardium, which is expressed by the elevation of the strength of contractions and frequency of heartbeats. Epinephrine and other sympathomimetic drugs with ¡2-adreno-agonist properties are responsible for relaxation of bronchial muscles and an increase in bronchodilatation. Moreover, the a-adrenergic agonist activity of epinephrine is exhibited through the contraction of pulmonary vessels and the development of antiedema effects.
It is used in anaphylactic, allergic, and other hypersensitive reactions, as an agent to increase blood pressure in hypotension, as a broncholytic in pulmonary edema, as an antiedema agent in othorinolaringology (LOR) and in ophthalmological practice, and also to prolong the action of local anesthetics.
Epinephrine is used for relieving bronchial asthma, revival from anaphylactic shock, in hyperglycemic coma, and allergic reactions. It is used as a local vasoconstrictor, in particular, in ophthalmology for reducing intraocular pressure.
There is a large number of synonyms for epinephrine: adnephrine, adrenat, biorenin, epinal, hemostatin, nieralin, syndernin, and others. However, the main synonym of epi-nephrine is adrenaline.
Norepinephrine: Norepinephrine, l-1-(3,4-dihydroxyphenyl)-2-aminoethanol (11.1.4), is synthesized by two methods starting from 3,4-dihydroxybenzaldehyde. According to the first method, the indicated aldehyde is transformed into the cyanohydrin (11.1.3) by reaction with hydrogen cyanide, which is then reduced into norepinephrine (11.1.5) [11,12].
HO HO HO
)=\ O HCN >=\ OH [H] >=\ '°H HO—d h—C-H -► HO—^ h— CH-CN -HO^^/)—CH-CH2-NH2
The second method consists of the condensation of diacetate of the same aldehyde with nitromethane, which forms (3,4-diacetoxyphenyl)-2-nitroethanol (11.1.5). Then the nitro group is reduced and the product (11.1.6) is hydrolyzed into the desired norepinephrine (11.1.4) [4,9,13,14].
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