Pharmacology of an Indian-snuff obtained from Amazonian Maquira sclerophylla.

The powdered bark of Maquira sclerophylla is consumed as snuff in north Brazil. Both the crude and the purified hydrosoluble extract (WP) injected i.p. in the dose range of 0.05-0.5 g/kg induced hyperexcitability, tremors, motor incoordination, ataxia, quietness and muscle relaxation in rats. The effects were progressive, dose-related and reversed after 30 min. Anesthetized rats, guinea-pigs and dogs injected with the purified extract (10-50 mg/kg, i.v.) showed a biphasic change of carotid blood pressure. The early and transient hypotension was blocked by atropine but not by vagotomy: the secondary hypertension was long lasting and sustained for over 30 min. The hypertension was shortened but not blocked after ganglionic blockade or reserpine treatment. Either pithing or alpha receptor blockade with yohimbine reduced both effects of the extract. Guinea-pigs and dogs were more responsive than rats and died by heart arrest. Incubation of WP (20 micrograms/ml) increased both the rate and force of contraction of isolated guinea-pig right atria by 2 and 5 times, respectively. Propranolol (4 micrograms/ml) blocked the chronotropic effect but did not decrease the inotropic effect. In electrically driven guinea-pig left atria, WP (10 micrograms/ml) increased the force of contraction by 80% and the maximum rate of force development by 60%, but did not change the time to peak tension, the time to 50% relaxation, or the rate of relaxation. These cardiovascular effects resemble those of digitalis-like drugs. Cardenolides were detected in WP by phytochemical screening.