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 ]]).