Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Biológicas. Programa de Pós-graduação em Farmacologia.The nociceptive effects of Endothelin-1 (ET) are well-known. This peptide is synthesized by cleavage of Big ET-1 by Endothelin Converting Enzyme (ECE), however, Big ET-1 can be also cleaved by mast cell-derived chymase to ET-1(1-31), which can be converted to ET-1 by the enzyme neutral endopeptidase-24.11 (NEP). The present study aimed to assess, pharmacologically, the ability of ET-1(1-31) to induce nociception and mechanical hypernociception in the hind paw of mice and compare its effects with those evoked by ET-1 and Big ET-1. The intra-plantar (i.pl) injection of ET-1 (3 to 30 pmol), ET-1(1-31) (30 to 100 pmol) or Big ET-1 (30 to 100 pmol) induced dose-dependent nociception and hypernociception. Local pretreatment of the animals with thiorphan (NEP inhibitor, 300 nmol, i.pl.) or phosphoramidon (NEP and ECE inhibitors, 100 nmol, i.pl.), reduced nociception induced by ET-1(1-31) (10 pmol) or by ET-1(1-31) and Big ET-1 (30 pmol), respectively. On the other hand, pre treatment with chymostatin (chymase inhibitor, 100 nmol) did not alter the nociception induced by ET-1, ET-1 (1-31) or Big ET-1. Mast cell degranulation by i.pl. injection of compound 48/80 (0.05 to 1 ìg) or OVA (0.05 to 1 ìg) also evoked nociception and mechanical hypernociception. The association of Big ET-1 (30 pmol) with sub-effective doses of compound 48/80 (0.1 ìg) or OVA (0.05 ìg) resulted in potentiation of Big-ET-1-induced nociception by 93.5% e 154%, respectively. Pre-treatment with phosphoramidon (100 nmol) or chymostatin (100 nmol) reduced the nociception induced by Big ET-1 associated with compound 48/80 or OVA, while thiorphan was only able to reduce the nociception induced by the association of Big ET-1 plus compound 48/80 at 1000 nmol. Nociception induced by compound 48/80 (1.0 ìg) and OVA (0.3 ìg) was reduced by pretreatment with phosphoramidon or chymostatin or BQ-123 (selective ETBAB receptor antagonist, 10 nmol), while BQ-788 (selective ETBBB receptor antagonist, 10 nmol) and thiorphan (1000 nmol) reduced only nociception induced by OVA and compound 48/80, respectively. The results of the current study suggest that ET-1, formed via an alternative synthesis pathway, which involves formation of the intermediary peptide ET-1(1-31), contributes significantly to nociception induced by the activation of mast cells.