TRYPTAMINE-INDUCED DRUG EFFECTS INSENSITIVE TO SEROTONINERGIC ANTAGONISTS - EVIDENCE OF SPECIFIC TRYPTAMINERGIC RECEPTOR STIMULATION

The drug effects of tryptamine and 5‐hydroxytryptophan (5‐HTP) in the rabbit were compared following monoamine oxidase inhibition and various drug pretreatments. Both agents evoked hyperthermia and behavioural excitation; tryptamine but not 5‐HTP also produced forepaw clonic activity. Serotoninergic receptor blockers abolished the effects of 5‐HTP but only weakly influenced tryptamine responses. Both tryptamine and 5‐HTP effects were potentiated by fluoxetine. Methergoline, a putative tryptaminergic receptor blocker, antagonized tryptamine‐induced hyperthermia and forepaw clonus but did not influence 5‐HTP responses. It is postulated that while 5‐HTP produces its effects through a serotoninergic mechanism, some of the responses to tryptamine result from activation of a specific tryptamine‐sensitive mechanism. 1978 Royal Pharmaceutical Society of Great Britain