Antagonism of 5-hydroxytryptamine2 receptor-mediated phosphatidylinositol turnover by d-lysergic acid diethylamide.
The interactions of the indolealkylamine hallucinogen d-lysergic acid diethylamide (d-LSD) and two phenalkylamine hallucinogens, 2,5-dimethoxy-4-bromoamphetamine (DOB) and 2,5-dimethoxy-4-iodoamphetamine (DOI), with 5-hydroxytryptamine2 (5-HT2) receptors were analyzed in rat cortex using both radioligand binding techniques and biochemical measurements of phosphatidylinositol (PI) turnover. 5-HT2 binding sites were labeled by [3H]ketanserin. DOB and DOI displayed decreased affinity for 5-HT2 sites in the presence of 10(-4) M GTP, whereas the ability of d-LSD to compete for these sites was not affected by the presence of 10(-4) M GTP. Moreover, the Hill slope of the d-LSD competition curve was unity in both the absence and presence of 10(-4) M GTP. These findings suggest that d-LSD is an antagonist at 5-HT2 receptors. PI turnover studies in rat cortex showed that at 10(-5) M concentrations d-LSD, DOB and DOI display partial agonist activity in comparison to 10(-5) 5-HT. Stimulation of PI turnover by 5-HT, DOB and DOI was inhibited by the 5-HT2 antagonist ketanserin (10(-6) M). The d-LSD PI signal was not affected by the presence of ketanserin. In addition, nanomolar concentrations of d-LSD did not stimulate PI turnover in rat cortex. Moreover, nanomolar concentrations of d-LSD are able to significantly antagonize the stimulatory effect of 10(-5) M 5-HT on PI turnover. These data suggest that d-LSD acts as an antagonist at 5-HT2 receptors in rat cortex. At high concentrations (greater than 1 microM) d-LSD stimulates low-level PI turnover via a non-5-HT2 receptor-mediated mechanism.
Pierce
P A
PA
Department of Neurology, Stanford University Medical Center, California.
Peroutka
S J
SJ
D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine / Q000031:analogs & derivatives / Q000494:pharmacology; D000662:Amphetamines / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006160:Guanosine Triphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007650:Ketanserin / Q000378:metabolism / Q000494:pharmacology; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects*
D000662:Amphetamines; D010716:Phosphatidylinositols; D011985:Receptors, Serotonin; D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine; C003943:2,5-dimethoxy-4-bromoamphetamine; D006160:Guanosine Triphosphate; D008238:Lysergic Acid Diethylamide; D007650:Ketanserin; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine