Muscle relaxants pharmacological specifications

It is generally accepted that the pharmacology of benzodiazepine derivatives is identical qualitatively but varies quantitatively. In other words, the sedative, hypnotic, anticonvulsant, muscle relaxant, and anxiolytic properties reside to various degrees in all of them. Nevertheless, they do exhibit pharmacological specificity, making it necessary to select a particular drug for its desired therapeutic effect. 

Such compounds often exhibit chemical and spectral behaviour which is specifically characteristic of the dimeric structure. Also of paramount interest are the specific pharmacological properties of certain of these alkaloids, such as the muscle relaxation action of the curare alkaloids and the anti-leukemia activity of the Vinca alkaloids leurocristine and vinblastine. Such aspects will be discussed in the last two sections of the review. 

Fascinating plant folklore and ethnopharmacology leads to medicinal potential. Examples are the muscle relaxants based on the arrow poison, curare, from species of Chondrodendron, and the antimalarials derived from species of Cinchona and Artemisia. The methods of detection of pharmacological activity have become increasingly reliable and specific, frequently involving enzymes in bioassays and avoiding the use of laboratory animals. By using bioassay linked fractionation of crude plant juices or extracts, compounds can be specifically... 

In addition, vinpocetine selectively inhibits a specific calcium, calmodulin-dependent cycHc nucleotide phosphodiesterase (PDF) isozyme (16). As a result of this inhibition, cycHc guanosine 5 -monophosphate (GMP) levels increase. Relaxation of smooth muscle seems to be dependent on the activation of cychc GMP-dependent protein kinase (17), thus this property may account for the vasodilator activity of vinpocetine. A review of the pharmacology of vinpocetine is available (18). 

In summary, adrenergic receptors can be subclassified according to their location and affinity for specific pharmacologic agents. Table 18-2 summarizes the receptor subtypes that are located on the primary organs and tissues in the body, and the associated response when the receptor is stimulated. Exactly which receptor subtype is located on any given tissue depends on the tissue in question. Note that some tissues may have two or more different subtypes of adrenergic receptor (e.g., skeletal muscle arterioles appear to have alpha-1 and beta-2 receptors). Also, the response of a tissue when the receptor is stimulated is dependent on the specific receptor-cell interaction. Stimulation of the vascular alpha-1 receptor, for instance, results in smooth-muscle contraction and vasoconstriction, whereas stimulation of the intestinal alpha-1 receptor results in relaxation and decreased intestinal motility. This difference is caused by the way the receptor is coupled to the cell s internal biochemistry at each location. As discussed in Chapter 4, the surface receptor at one cell may be coupled to the... 

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