Opposite Effects on Human Distal Colon Motility of Two Postulated Alpha2‐Antagonists (Mianserin and Chlorprothixene) and One Alpha2‐Agonist (Clonidine)

The effects of two postulated alpha 2-antagonists (mianserin and chlorprothixene) and an accepted alpha 2-agonist (clonidine) on the distal colon motility in five healthy subjects were investigated. Opposite effects were induced by these two kinds of drugs. Distinct and characteristic motility responses were obtained from subjects with low distal colon tone and subjects with high distal colon tone. In addition, different and typical behavior responses paralleled motility changes in the two types of subjects. These results suggest that, at the doses employed in this study, both mianserin and chlorprothixene behave as alpha 2-antagonists when tested on human distal colon motility against a known alpha 2-agonist such as clonidine.