These responses were effectively blocked by the 5-HT1B receptor antagonist, isamoltane, the 5-HT1B/<< 5-HT2 receptor >> antagonist, [[ methiothepin ]], and the eNOS selective antagonists (0.01-10 microM): L-Nomega -monomethyl-L-arginine (L-NMMA) and L-N omega-iminoethyl-L-ornithine (L-NIO).