Poster 210 - Relaxant activity of a proteic toxin from Leptodactylus pentadactylus skin on rat

Poster 210. Congresso da Sociedade Brasileira de Toxinologia, 8., Symposium of the Pan American Section of the International Society on Toxinology, 8., 2004, Angra dos Reis, Brasil. Abstracts... J. Venom. Anim. Toxins incl.Trop. Dis., 2004, 10, 3, p.569.

Relaxant Activity Of A Proteic Toxin From Leptodactylus pentadactylus Skin On Rat Aorta

^{1Montenegro, C.M.; ²Pires, A.F; ¹Limaverde, P.T.; ²Meireles, A.V.P.; ²Assreuy, A.M.S.; ¹Cardi, B.A.; ²Criddle, D.N and ¹Carvalho, K.M.}

1 Lab. de Toxinologia, Instituto Superior de Ciências Biomédicas, UECE, Fortaleza, CE; 2 LAFACI, Instituto Superior de Ciências Biomédicas, UECE, Fortaleza, CE.

Previous studies from our group have demonstrated that Lp8 a proteic toxin purified from L. pentadactylus, an amphibian encountered in the northeast of Brazil, possesses a hypotensive effect in vivo and endothelium-dependent vasorelaxant activity in vitro. The aim of this study was to evaluate the nature of the endothelium-derived releasing factor(s) involved in Lp8-induced relaxation of rat isolated aorta. Aortic rings from Wistar rats (200-250g) were mounted in organ chambers containing 10ml of Tyrode solution at 37°C, bubbled with 5% CO2/ 95% O2. Contractile responses were recorded from tissues, with or without an intact endothelium, using conventional techniques. Aortic rings were precontracted with KCl (60mM; K60) and, on formation of a stable tonic response, Lp8 was added in increasing cumulative concentrations (10^-5-3x10^-2µg/ml) using a ten minute contact time at each concentration. K60 induced tonic contractions of amplitude 0.76±0.09g (n=7). In tissues in which the endothelium had been mechanically removed, Lp8 did not affect K60-induced contractions. However, in aortic rings with an intact endothelium, Lp8 induced significant relaxation (IC50=0.52+0.1µg/ml; p<0.05) starting at a concentration of 10^-4mg/ml, with a maximal relaxation of 58.42+6.54% (n=6) of induced tone occurring at 3x10^-2mg/ml, suggesting that endothelium-derived hyperpolarizing factor, which opens membrane K-channels, was not involved. In contrast, Lp8-induced relaxation of KCl-induced contractions was completely blocked by L-NAME (100µM, n=8), implicating the involvement of nitric oxide in Lp8-mediated effects. The present data show that amphibian Lp8 induces endothelium-dependent vasorelaxation via release of nitric oxide coherent with a previously reported hypotensive effect in vivo.