Injections of D-lysergic acid diethylamide (LSD) reduce the turnover rate of the neurotransmitter serotonin (5-hydroxytryptamine) in rat brain, measured by the conversion of radiolabeled tryptophan into radiolabeled serotonin. In contrast, a related compound, 2-bromolysergic acid diethylamide, given at five times the dose of LSD, does not alter this conversion rate. The finding is discussed in relation to LSD's effects on brain serotonergic neurons and its ability to produce psychosis-like symptoms.
The tranquilizing drugs Frenquel, chlorpromazine, and reserpine block serotonin-induced contractions in the uterus of spayed rats, without affecting responses to acetylcholine or oxytocin. Reserpine's blocking effect lasts longer than chlorpromazine's, and Frenquel's is shortest. Mescaline enhances serotonin's effects and, at high doses, directly contracts the uterus, an action not blocked by atropine. High concentrations of LSD (1 γ/L) antagonize both serotonin- and mescaline-induced uterine activity, whereas low concentrations (0.05 to 0.2 γ/L) facilitate these effects.