N(1)-substituted ergolines and tryptamines show species differences for the agonist-labeled 5-HT2 receptor.
Previous studies indicated that selected ergolines and tryptamines showed species differences for affinity to the antagonist-labeled 5-HT2 receptor. The present study examined these same compounds for affinity at the agonist-labeled 5-HT2 receptor in rat and squirrel monkey cortical homogenates using [125I]DOI ([125I]1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane). As seen with the antagonist-labeled 5-HT2 receptor, N(1) alkyl substitution of either the ergolines or tryptamines resulted in a slight increase or no effect on their affinity for the agonist-labeled rat 5-HT2 receptor. In contrast, these same N(1) substitutions resulted in significant decreases in affinity for the agonist-labeled monkey 5-HT2 receptor. It was also noted that N(1)-unsubstituted ergolines and tryptamines (such as ergonovine, LY86057, LY193525 and 5-methoxytryptamine) tended to have higher affinity for the monkey versus the rat agonist-labeled receptor. However, the N(1) alkyl-substituted ergolines and tryptamines (such as mesulergine, LY53857, amesergide, N(1)-isopropyltryptamine and N(1)-isopropyl-5-methoxytryptamine) showed significantly lower affinity for the monkey versus the rat 5-HT2 receptor. These data suggest that, at least in relation to the N(1) position, ergolines and tryptamines bind in a similar orientation. These results are also discussed in terms of what amino acid differences between species may account for this structure-activity relationship.
Johnson
M P
MP
Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285.
Audia
J E
JE
Nissen
J S
JS
Nelson
D L
DL
D000662:Amphetamines / Q000378:metabolism*; D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism; D004873:Ergolines / Q000378:metabolism*; D004874:Ergonovine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000378:metabolism*; D012453:Saimiri; D012702:Serotonin Antagonists / Q000378:metabolism*; D017366:Serotonin Receptor Agonists / Q000378:metabolism*; D013045:Species Specificity; D013329:Structure-Activity Relationship; D014363:Tryptamines / Q000378:metabolism*
D000662:Amphetamines; D004873:Ergolines; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D014363:Tryptamines; C066736:amesergide; C032663:LY 53857; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine; D004874:Ergonovine