An action of 5-hydroxytryptamine on adrenaline receptors.
Contractions of isolated strips of cat spleen due to 5-hydroxytryptamine, adrenaline, histamine and acetylcholine were antagonized by phenoxybenzamine. Responses to both 5-hydroxytryptamine and adrenaline were not blocked in strips which were protected by a high concentration of either 5-hydroxytryptamine or adrenaline throughout exposure to phenoxybenzamine. The contraction due to a large dose of 5-hydroxytryptamine lasted less than 1 hr even when the drug was still present. Strips thus desensitized to 5-hydroxytryptamine responded normally to acetylcholine and histamine but did not respond to adrenaline. The actions of 5-hydroxytryptamine and adrenaline were blocked by 2-bromolysergic acid diethylamide or by dihydroergotamine. These results indicated that 5-hydroxytryptamine and adrenaline act on the same receptors. Cocaine potentiated the action of adrenaline but inhibited the action of 5-hydroxytryptamine. The sensitivity to 5-hydroxytryptamine of spleen strips from cats treated 24 hr earlier with reserpine was only one-fiftieth of that of normal strips. Cocaine potentiated the action of 5-hydroxytryptamine on strips from reserpine-treated cats. A high concentration of 5-hydroxytryptamine in spleen strips from reserpine-treated cats and in cocaine-treated strips prevented phenoxybenzamine from blocking the actions of adrenaline. The effects of tyramine on spleen strips almost exactly paralleled the effects of 5-hydroxytryptamine. Strips showing tachyphylaxis to tyramine did not respond to 5-hydroxytryptamine. It is concluded that 5-hydroxytryptamine has a dual action, viz., a major action due to release of stored noradrenaline and a minor direct action of adrenaline receptors.
D000109:Acetylcholine; D000818:Animals; D002415:Cats; D003042:Cocaine; D004837:Epinephrine; D004878:Ergotamine; D006632:Histamine; D008238:Lysergic Acid Diethylamide / Q000031:analogs & derivatives; D009638:Norepinephrine; D010643:Phenoxybenzamine; D012110:Reserpine; D011984:Sensory Receptor Cells; D012701:Serotonin; D013154:Spleen; D014439:Tyramine
D010643:Phenoxybenzamine; D012701:Serotonin; D006632:Histamine; D012110:Reserpine; D008238:Lysergic Acid Diethylamide; D003042:Cocaine; C084642:2-bromolysergic acid diethylamide; D000109:Acetylcholine; D004878:Ergotamine; D009638:Norepinephrine; D014439:Tyramine; D004837:Epinephrine
ACETYLCHOLINE; COCAINE; EPINEPHRINE; ERGOTAMINE; HISTAMINE; PHENOXYBENZAMINE; RECEPTORS, NEURAL; RESERPINE; SEROTONIN; SPLEEN; TYRAMINE