Characterization of 5-HT receptors mediating contraction and relaxation of the longitudinal muscle of guinea-pig distal colon in vitro

Abstract

A range of agonists and antagonists were used to characterize the receptors through which 5-hydroxytryptamine (5-HT) contracts and relaxes the longitudinal muscle of segments of guinea-pig distal colon, in vitro. 5-HT contracted the longitudinal muscle over the concentration range 10-9 to 10-4 mol/l. The 5-HT3 receptor agonist, 2-methyl-5-HT, produced concentration dependent contractions over the range 10-6 to 10-4 mol/l. 5-methoxytryptamine, an agonist at 5-HT4 receptors, caused contractions over a concentration range of 10-8 to 10-4 mol/l. The 5-HT4 antagonist, SDZ 205-557 (5 × 10-7 mol/l) substantially suppressed the responses to low concentrations of 5-HT and to 5-methoxytryptamine, but ..