Receptors involved n the action of 5-HT and tryptamine on the isolated rat stomach fundus preparation

Participation of α-adreniceptors in the effects of 5-HT and tryptamine on the isolated rat stomach fundus preparation was investigated. The effects of recognized anti-5-HT agents were also investigated to determine whether or not the same type of receptors was involved in the response of the rat fundus to 5-HT and tryptamine. Methylsergide was shown to be a very active, slowly reversible inhibitor of the 5-HT-induced contrations. The degree of inhibition was dependent on the time of pre-incubation and reached its maximum after approximately 2 hr. The α-adrenolytic agent piperoxan appeared to be a competitive antagonist of 5-HT. Piperoxan was able to prevent or reduce the anti-5-HT activity of mianserin, cyproheptadine and methysergide, indicating a common site of all action. All antagonists affected the 5-HT contractions more than those induced by tryptamine. It is concluded, that the effect of 5-HT on the isolated rat stomach fundus is the result of an interaction of 5-HT with one type of receptor. This receptor probably is the classical D-tryptamine receptor. The response to tryptamine is the result of an interaction by tryptamine with two different types of receptors. One type of receptors is identical to the receptor mediating the response to 5-HT, whilst the other type of receptor is more resistant to inhibition by emthylsergide, piperoxan, cyproheptadine or mianserin, and might be identical with the PRT-receptor, described earlier as being resistant to inhibition by phenoxybenzamine.