RESUMO
The relaxant effect of sumatriptan, a 5-HT(1B/1D) receptor agonist, on the rat anococcygeus muscle was investigated. Sumatriptan induced concentration-dependent relaxations of the phenylephrine-precontracted rat anococcygeus muscle. N(G)-nitro-L-arginine, methylene blue, glibenclamide, tetrodotoxin, indomethacin, GR 113808, GR 55562, methysergide, ketanserin, ICS 205930, clozapine, methiothepin, metergoline, mesulergine, and ritanserin did not inhibit the relaxations induced by sumatriptan. Sumatriptan converted calcium-induced contractions into relaxations in the preparations depolarized by a calcium-free, high-potassium solution. In membrane preparations obtained from the rat anococcygeus muscle, the basal rate of cAMP production by adenylate cyclase was 4.77 +/- 0.02 pmol/mg protein/min (n = 15). The enzyme activity was increased to 104 +/- 51.7 pmol/mg protein/min by forskolin (10(-4) mol/l), but did not change in the presence of sumatriptan. The mRNA expression of 5-HT(1B), 5-HT(1D), and 5-HT(7) receptors was not observed in the rat anococcygeus muscle. The results indicate that sumatriptan causes relaxation of the precontracted rat anococcygeus muscle by a calcium-antagonistic activity.
