Abstract
The powdered bark obtained from Maquira sclerophylla Ducke is a snuff used by Amazonian natives. Pharmacological studies on rodents, guinea-pigs, rabbits and dogs revealed cardiovascular changes as the major effects produced by the polar phase of the bark ethanol extract. Oriented by this pharmacological activity a cardenolide fraction was chemically purified from the crude extract. Both crude extract and the purified fraction produced a positive inotropic effect in isolated heart preparations from guinea-pigs and rabbits, and inhibited the Na+, K+-ATPase activity of the enzyme isolated from bovine ventricles. The fraction yielded two major purified cardenolides identified as Maquiroside A (C30H46O8) and Cymarin (C30H44O9). Simultaneous intracellular recordings of the resting membrane potential (RMP) and miniature endplate potentials in rat diaphragm muscle fibres showed that the effect of the purified fraction predominated on the motor nerve terminals enhancing the spontaneous transmitter release, without major changes of RMP values. Comparatively, the effect of ouabain prevailed on the muscle fibre membrane. Considering that both effects depend on the Na+, K+-ATPase activity, the results indicated that the compounds derived from Maquira exert differential actions on this enzyme in the nerve and muscle membrane. These observations may explain the use of this toxic snuff in native festivities. © 1997 by John Wiley & Sons, Ltd.
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