PHARMACOLOGICAL CHARACTERIZATION OF THE EFFECTS INDUCED BY Tityus serrulatus VENOM IN THE RAT RETRACTOR PENIS MUSCLE 

BOMFIM, J.H.G.G.(1), GIGLIO, J.R.(2), DE OLIVEIRA, A.M.(1), GODOY, M.A.F.(3), ARANTES, E.C.(1)

(1)Departamento de Física e Química, FCFRP, USP, (20Departamento de Bioquímica e Imunologia, (3)Departamento de Farmacologia, FMRP, USP, Ribeirão Preto, SP, Brasil

OBJECTIVES:The aim of this study is to investigate the contractile and relaxant responses induced by Tityus serrulatus venom (TsV) in rat isolated retractor penis muscle (RPM).

METHODS AND RESULTS: RPM was isolated and mounted under 0,6 g resting tension in 5 ml organ bath containing physiological Krebs solution, maintained at 37^o C and gassed with 5% carbon dioxide in oxygen. The results were recorded in a Harvard Universal oscillograph connected to a 133 Pentium. TsV (1-60 mg/ml) induced a concentration-dependent contractile response (E_máx = 66.23 ±6.2% n=6 , pD₂ = -1.01). In the presence of prazosin (1mM, 20 min) and guanethidine(30 mM, 10 min), TsV did not produce any contractile effect. The  relaxation response was performed by contracting the muscle with bethanechol(100 mM), in the presence of prazosin (1mM, 20 min) and guanethidine (30 mM, 10 min), associated or not with L-NAME (1mM, 30 min). TsV (1-60 mg/ml) induced a concentration-dependent relaxant response (E_máx= 52.32 ±7.5%  n=7  , pD₂ = -1.08) in the absence of L-NAME. In the presence of  L-NAME, TsV did not produce any relaxant  response.

CONCLUSION: TsVinduces a contractile response in rat RPM due the norepinephrine release, which was confirmed with simpathetic specific inhibitors (prazosin and guanethidine).The relaxant response is dependent on nitric oxide release, probably from nitrergic nerves, as shown by L-NAME assay. 

CORRESPONDENCE TO:

BOMFIM, J.H.G.G., Avenida do Café s/n, Departamento de Física e Química, FCFRP-USP, Ribeirão Preto, SP, CEP: 14040-903, Brasil, Email: henrique@fcfrp.usp.br