Sparteine pharmacological action

Sparteine is the most important uterine stimulant of this group, which inclhdes also d-lupanine, lupinine, trilupine, and cytisine. Nicotine is discussed here also because of a very close similarity to cytisine in its pharmacological actions. 

In general, we find a series of related compounds in each plant often a few major metabolites and several minor components which differ in the position of their substituents (Fig. 9.4). Sparteine and lupanine only differ by a single keto function, but their modes of action differ substantially (Fig. 9.2). The profile usually varies between plant organs, within developmental periods, and sometimes even diurnally (e g., in lupin alkaloids60). Also marked differences can usually be seen between individual plants of a single population, even more so between members of different populations. This variation, that is part of the apparent evolutionary arms race between plants and herbivores, makes adaptations by herbivores more difficult, since even small changes in chemistry can be the base for new pharmacological activities. 

Sparteine is a drug with antiarrhythmic properties. It has been deduced from pharmacological and electrophysiological studies that sparteine acts via a reduction of the Na inward current, e.g. during the upstroke of cardiac action potentials. This process was elucidated by the determination of sodium currents, in isolated muscle fibbers, by loose patch clamp measurements [236]. The IC50 value for half-maximal blocking of the sodium current was 168.8 )iM, which is in accordance witli the antiarrhythmic activity of sparteine. The importance of sparteine on Na channels inhibition was further analysed because of its potencial strong interference in neuronal transmission, particularly in herbivores. This emphasizes the role of sparteine as a chemical defence compound for the plants that produce it. 

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