Ação vasoativa do veneno do sapo Rhinella marina em aorta de ratos Wistar

Abstract

Rhinella marina toad is very abundant in Brazil. Its poison has a large amount of bufadienolides, which are largely studied due to its influence on NA+/K+ ATPase. Our hypothesis is that R. marina poison has a bufadienolid-mediated vasoconstrictor action. Thus, our aim was to characterize a vasoactive action of this venom in the aorta of male Wistar rats. For this, the poison was first collected and the alcohol extract was prepared, which was used in the experiments. After, vascular reactivity was performed in aortic segments (with and without endothelium) for the concentrations 0,2 µg/ml, 2 µg/ml, 5 µg/ml and 7 µg/ml of the gross poison extract. We evaluated the possible mechanisms of action involved in vasoconstrictor response and the NA+ /K+ ATPase activity. We also tested the vascular action of the isolated compound marinobufagenin, which is one of the bufadienolides present in the poison. Poison-induced vasoconstriction was observed in the presence and the absence of endothelium. The presence of L-NAME, a nitric oxide synthase inhibitor, increased the contractile response, suggesting endothelial modulation of this response. About the mechanisms, we observed that the segments incubated with losartan, nifedipine and prazosin decreased contractility, indicating that this action occurs partially via angiotensin II AT1 receptors, L-type calcium channels and α1- adrenergic receptors, respectively. Importantly, the only blockade that completely abolished the contractile response of the venom was the α1-adrenergic receptor antagonist. There was no change in the contractile response to venom in the presence of cyclooxygenase (indomethacin) and reactive oxygen species (apocynin) pathway blockers. In the NA+ /K+ ATPase pump test, the aortas incubated with venom presented a higher percentage of vascular relaxation than the control, indicating that the venom acts enhancing the effect of tissue repolarization, and does not contribute to the venom-induced vascular contraction. Marinobufagenin compound showed no vasoactive response. Thus, the venom of the toad Rhinella marina has a potent vasocontrictive action, not associated with bufadienolides, and may be a possible candidate for the treatment of vascular diseases, as sepsis.