6). In a two-way ANOVA test, significant differences in the effect of treatment [F(3,35) = 41.06; P < 0.0001], time [F(7,35) = 6.46; P < 0.0001] and treatment-vs.-time interaction [F(21,245) = 1.679; P < 0.001] were observed. Post hoc analysis indicated that highest doses of A. paulensis crude venom

(60 and 40 μg/paw) induced an edematogenic effect that was observed during the whole experimentation period. Moreover, at the periods of 40, 90 and 120 min after venom injection, significant differences between the highest doses and the lowest (20 μg/paw) were observed. The evaluation of the records obtained in the in situ frog heart showed transient cardiac arrest produced by vagal stimulation and after administration of venom (500 μg) ( Fig. 7). The vagal stimulation led to a reduction on the contraction force (negative inotropic effect) and heart rate (negative chronotropic Selleckchem Adriamycin effect), well-known effects mediated by the release of acetylcholine

(ACh) from parasympathetic autonomic nerve terminals. These effects were reversible within 30 s. The crude venom also produced negative chronotropic and inotropic effects, causing cardiac arrest, which was reversible in about 2 min. The vagal stimulation effect was completely blocked in the presence of atropine (2 μg), a muscarinic receptor blocker. By adding crude venom (500 μg) in the heart pretreated find more with atropine, no changes in the electrical register were observed, indicating the blockade by atropine. The brief destabilization in the mechanical register could be explained

by the Frank–Starling mechanism, which illustrates the ability of the vertebrate heart to intrinsically modulate the rate and strength of cardiac muscle contractility in response to changes in atrial pressure driven by changes in venous return ( da Silva et al., 2011). The assay with the isolated frog ventricle strips confirmed the results obtained in the heart in situ ( Fig. 8). The crude venom (50 μg) caused a reduction in the strength of ventricle slice contraction (negative inotropic effect) similar to that produced by acetylcholine (0.25 μg). The same effect was reproduced with the “low molecular mass next fraction – LMMF” (12.5 μg), but not with the “protein fraction – PF” (50 μg). The administration of atropine (2 μg) to the bath caused a mild positive inotropic effect, which remained after administration of ACh, crude venom or LMMF. In the presence of atropine, the effects of these were no longer observed. The records of ACh (0.25 μg) and LMMF (12.5 μg) in presence of atropine (2 μg) were equal to that of “atropine plus venom”, shown in Fig. 8A, and therefore are not illustrated. Fig. 8B shows the reduction rate of muscle contraction obtained for each treatment. Statistically, the crude venom, LMMF and acetylcholine had similar negative inotropic effects. The protein fraction (PF) conversely did not show this effect.