Numerous plants are used as snakebite antidotes in Brazilian folk medicine, including Casearia sylvestris Swartz, popularly known as guaçatonga. In this study, we examined the action of a hydroalcoholic extract from C. sylvestris on the neuromuscular blockade caused by bothropstoxin-I (BthTX-I), a myotoxin from Bothrops jararacussu venom, in mouse isolated phrenic nerve-diaphragm (PND) preparations. Aqueous (8 and 12 mg/ml, n=4 and 5, respectively) and hydroalcoholic (12 mg/ml, n=12) extracts of the leaves of C. sylvestris caused facilitation in PND preparations followed by partial neuromuscular blockade. BthTX-I (20 µg/ml, n=4) caused 50% paralysis after 65±15 min (mean ± S.E.M). Preincubation (30 min at 37°C) of BthTX-I (20 µg/ml, n=4) with a concentration of the hydroalcoholic extract (4 mg/ml) that had no neuromuscular activity, such as the control (n=5), prevented the neuromuscular blockade caused by the toxin. This protection may be mediated by compounds such as flavonoids and phenols identified by thin-layer chromatography and colorimetric assays.

RESUMOParahancornia amapa é uma espécie endêmica do Estado do Amapá, na região Amazônica. Este estudo teve como objetivo avaliar a toxicidade aguda do extrato metanólico das cascas do caule de P. amapa. Diferentes concentrações do extrato foram adicionadas aos camarões de salmoura (Artemia salina) e a concentração letal média (CL 50 Preclinical acute toxicological evaluation of the methanolic stem bark extract of Parahancornia amapa (Apocynaceae)ABSTRACT Parahancornia amapa is an endemic plant species of Amapá in the Amazon region. This study aimed to evaluate the acute toxicity of methanol extract of the bark of P. amapa. Different concentrations of the extract were added to the brine shrimps (Artemia salina) and 50% lethality concentration (LC 50 ) was assessed. The results of the brine-shrimp assay indicated that the extract was found to be non-toxic. Acute toxicity was studied in Wistar rats (males and females) after single dose (2000 mg kg -1 ) by oral gavage. Food and water intake, body weight, general behavioral changes and mortality of animals were noted. Blood samples were collected for haematological and serum biochemical parameters measurements. Subsequently, they were euthanized and their organs (heart, kidneys, liver and lungs) subjected to macroscopic and histopathological analysis. There was no mortality or any sign of behavioral change or toxicity observed after oral administration of the extract. Nevertheless, it was observed a significant increase (p<0.05) on water intake of female rats treated with the extract of P. amapa (127.64 mL) when compared to control group (101.93 mL). A significant increase (p<0.05) in platelet count was also observed in both male (288.00x10 3 mm 3 ) and female (220.83x10 3 mm 3 ) rats that received the extract when compared to their respective control groups (128.33x10 3 mm 3 ; 109.50x10 3 mm 3 ). Histopathological changes were not related to the treatment with extract in any of the analyzed organs. These results suggest that P. amapa extract has a non-toxic effect.