Histamine receptors alpha 2 antagonist effects

In recent years traditional neuroleptics, as exemplified by chlorpromazine, have been structurally modified to produce drugs with greater affinity for dopamine receptors while retaining some of their activity on other receptor systems (e.g. on alpha] adrenoceptors, 5-HT2 receptors and histamine] receptors). In the non-phenothiazine series, a high degree of specificity for the D2 receptors has been achieved with sulpiride and pimozide, with haloperidol showing antagonistic effects on the 5-HT2 and alpha] adrenoceptors in addition to its selectivity for D2 receptors. The czs-(Z) isomers of the thioxanthines are potent neuroleptics that, in addition to... 

In the phenothiazine series of neuroleptics, thioridazine has less antimuscarinic potency than chlorpromazine, but appears to be equally active as an antagonist of 5-HT2 and D2 receptors like chlorpromazine, however, it is a potent alpha] adrenoceptor antagonist. In contrast, the potent phenothiazine neuroleptic perphenazine is only slightly less selective in blocking D2 receptors than haloperidol but, unlike the latter, has a greater antagonistic effect on histamine receptors. 

In addition to their affinity for dopamine receptors, which appears to be essential for their therapeutic activity, all neuroleptics in current clinical use have affinities for other types of neurotransmitter receptor. Mention has already been made of the side effects of the weaker neuroleptics such as chlorpromazine for histamine-1, muscarinic and alpha-1 adrenoceptors. However, it is now apparent that many of the newer, atypical, neuroleptics have an affinity for subtypes of 5-HT (particularly 5-HT2A) receptors which may be beneficial in reducing the frequency of extrapyramidal side effects. Thus neuroleptics may now be broadly classified into those which are selective antagonists of D2 receptors, those that are D2 and D3 receptor antagonists, those blocking both D and D2 receptors and, a most important group of novel neuroleptics, those that are antagonists of 5-HT2 and D2 receptors. 

Lidocaine hydrochloride is a local anesthetic/vasopressor preparation. Lidocaine stabilizes neuronal membranes by inhibiting the ionic fluxes required for the initiation and conduction of impulses, thereby effecting local anesthetic action. Epinephrine stimulates both alpha and beta receptors within sympathetic nervous system relaxes smooth muscle of bronchi and iris and is an antagonist of histamine. They are indicated for production of local or regional anesthesia by infiltration techniques such as percutaneous injection, by peripheral nerve block techniques such as brachial plexus and intercostals, and by central neural techniques such as lumbar and caudal epidural blocks. 

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