Caracterização farmacologica do relaxamento de corpo cavernoso de coelho induzido pelo veneno de Tityus serrulatus

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

Títyus serrufatus ís the most dangerous scorpíon of the subfamily Tityinae in Brazíl because of the high toxicity of its venom and its widespread distribution in populous urban centers of southeastern region of the country. The most important clinical manifestations of the human envenomation by Títyus serrulatus are intense local pain and an immediate local burning . sensation which may last from few minutes to several hours. These manifestations may be accompanied by autonomic dysfunctions such as vomiting, diaphoresis, tachycardia, mydriasis, tachypnea, excessive salivation, arterial pressure disturbances, tremors, etc. Tityus serrufatus . venom is known to act on nerve endings of the autonomic nervous system to stimulate the release of either acetylcholine or catecholamines from different organs and tissues. The erectile tissues from different animal species are innervated by adrenergic excitatory, cholinergic inhibitory and non-adrenergic non-cho!inergic (NANC) inhibitory nerve fibers which in ~ turn is believed to play a pivotal rore in the neural mechanisms involved in penile erection through the release of NO. Thus, the potential sources of NO production in the rabbit corpus cavernosum t preparation employed in this study are both NANC nerves and the endothelium covering the network of sinusoidal capillaries supplying the cavernosal tissue. Since NANC nerve stimulation . causes corpus cavernosum relaxation, we have investigated the effects of Tityu s serrulatus scorpion venom on the rabbit isolated corpus cavernosum. The effect of Tityus serrulatus scorpion venom and its fractions on the rabbit isollated corpus cavernosum (RbCC) was investigated using a bioassay cascade. The tissues were continuously infused with indomethacin (5.6 µM) to inhibit the generation of cyclooxygenase products. Dried Tityus serrufatus venom (400 mg) was purified using a CM-cellulose-52 column. Tityus serrufatus venom (3-100 1l9), acetylcholine (ACh; 0.3-30 nmol) and glyceryl trinitrate (GTN;0.5-10nmol) dose-dependently relaxed RbCC preparations precontracted with noradrenaline (3µM). The non-specific NO synthase (NOS) inhibitors Nw-nitro-L-arginine methyl ester (L-NAME; 10 µM), Nw-nitro-monomethyl-L-arginine (L-NMMA; 10 µM) and NG -iminoethyl-L-ornithine (L-NIO; . 30 µM) increased the tone of the RbCC tissues and markedly reduced both ACh- and Tityus serrulatus venom-induced RbCC relaxations without affecting those evoked by GTN. The inhibitory effect was reversed by infusion of L-arginine (300 µM), but not D-arginine (300 µM). The neuronal NOS inhibitor 1-(2-trifluoromethylphenyl) imidazole (TRIM, 100µM) affected neither the tone of the RbCC nor the relaxations induced by ACh, bradykinin (Bk), Tityus serrulatus venom and GTN. TRIM was approximately 1,000 times less potent than L-NAME in inhibiting rabbit cerebellar NOS ín vítro, as measured by the conversion of [3H]-L-arginine to [3H]-L-citrulline. The selective soluble guanylate cyclase inhibitor 1 H-[1 ,2,4] oxadiazolo [4,3,-alquinoxalin-1one] (OQD; 30 µM) also increased the basal tone of the RbCC and abolished the relaxations. induced by the agonists mentioned above. Methylene blue (30 µM) also inhibited the relaxations induced by Tityus serrulatus venom but, in contrast to OQD, the inhibition was irreversible. The protease inhibitor aprotinín (TrasylolÒ; 10µg.ml-1 the muscarini receptor antagonist atropine (1 IlM) and the bradykinín 82 receptor antagonist Hoe 140 (D-Arg-[Hyp3,Thi5,D-Tie, Oic8]-BK; 50 nM) did not affect the RbCC relaxations induced by Tityus serrulatus venom. Potassium channel antagonists such as glybenclamide (10 µM), apamin (0.1 µM), charybdotoxin (0.1 µM) and . tetraethylammonium (10 µM) also failed to affect the venom-induced relaxations. Capsaicin (3 and 10 nmol) relaxed the RbCC tissues in a dose-dependent and non tachyphylactic manner. Ruthenium red (30 µM), an inhibitor of capsaicin-induced responses, markedly reduced the RbCC relaxations caused by capsaicin, but failed to affect the RbCC . relaxations induced by Tityus serrulatus venom. L-NAME (10 µM) had no effect on the capsaicin induced RbCC relaxations. On the other hand, the sodium channel blocker tetrodotoxin (TTX; 1µM) abolisheçi the RbCC relaxations induced by Tityus serrulatus venom without affecting those evoked by capsaicin, ACh and GTN. Tetrodotoxin (1 µM) also promptly reversed the response to the venom when infused during the relaxation phase.The bioassay cascade of thirteen different toxin components purified from the Whole venom revealed that only fractions X, XI and XII caused dose-dependent RbCC relaxations and this was markedly reduced by either TTX (1 µM) or L-NAME (10 µM). We propose therefore that Tityus serrulatus venom acts selectively on NANC fibers, possibly nitrergic nerves, and that the NO generated in the nerve diffuses through the nerve endings to relax the adjacent vascular smooth muscle. Indeed, neuronal NOS (bNOS) has been detected in both the rat and human penis using an specific NOS antibody and immunohistochemistry. The findings that TRIM, a specific neuronal NOS inhibitor in the mouse, did not affect the NO release induced by Tityus serrulatus venom, may reflect its reduced potency on the rabbit enzyme.

ASSUNTO(S)

ereção peniana oxido nitrico

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