5−Hydroxytryptamine desensitization fails to modify GABA-induced inhibitory responses in the guinea-pig colon

Abstract
In segments of guinea-pig colon, treated with 1 μm hyoscine, a 5−HT desensitization procedure that decreased the potency of 5−HT 41−fold in relaxing the longitudinal musculature, failed to modify the non-adrenergic GABA-induced inhibitory responses, suggesting that the action of GABA in this preparation is not 5−HT-mediated. These results are at variance with those obtained in the guinea-pig ileum where 5−HT seems to play a role in GABA-induced cholinergic contractions.