Two kinds of tryptamine receptor. 1957

Abstract

There are two kinds of tryptamine receptor in the guinea-pig ileum, namely the M receptors which can be blocked with morphine and the D receptors which can be blocked with dibenzyline. Atropine, an atropine-like drug, cocaine, and methadone inhibit effects due to the M receptors, even after dibenzyline, but have no additional effect after morphine. Lysergic acid diethylamide, dihydroergotamine and 5-benzyloxygramine inhibit effects due to the D receptors, even after morphine, but have no additional effect after dibenzyline. The M receptors are probably in the nervous tissue and the D receptors are probably in the muscles.

Fig. 1

Guinea-pig ileum. Contractions due to 5-HT (HT), nicotine (N) and histamine (H). Doses μg. in 2 ml. bath. Above with morphine (1 μg./ml.). Effects on D receptors unchanged by atropine (0.1 μg./ml.) from 18 min. onwards. Dose-ratio= 1.3. Below after dibenzyline (0.1 μg./ml. for 30 min.). Effects on M receptors inhibited utropine (0.1 μg./ml.) from 38 min. onwards. Dose-ratio > 300 for 5-HT.

Fig. 2

Records as Fig. 1. Above with morphine (1 μg./ml.). Effects on D receptors inhibited by 5-bcnzyloxygramine (1 μg./ml.) from 38 min. onwards. Dose-ratio 1.3 = 50 for 5-HT. Below after dibenzyline (0.1 μg./ml. for 30 min). Effects on M receptors almost unchanged by 5-benzyloxygramine from 50 min. onwards. Dose-ratio = 2.