4-(2'-Methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p-iodobenzamido]ethyl] piperazine and 4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p- fluorobenzamido]ethyl]piperazine, two new antagonists at pre- and postsynaptic serotonin-1A receptors.
p-MPPI [4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p-iodobenzamido] ethylpiperazine] and p-MPPF [4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p- fluorobenzamido]ethyl]piperazine] competitively antagonized 5-HT1A receptor activation in the rat, as measured by hypothermia, forepaw treading and 5-HT turnover; they exhibited to partial agonist activity on any of these measures. When given i.p., p-MPPI and p-MPPF dose-dependently antagonized the hypothermia induced by 8-hydroxy-2- (di-n-propylamino)tetralin (8-OH-DPAT) (0.5 mg/kg), with approximate ID50 of 5 and 3 mg/kg, respectively. The inhibitory effect caused by a fixed dose of p-MPPI (6 mg/kg) or p-MPPF (3 mg/kg) was surmounted by higher doses of 8-OH-DPAT. p-MPPI and p-MPPF also attenuated the hypothermia induced by gepirone. Forepaw treading caused by 8-OH-DPAT (2 mg/kg) in reserpine-pretreated rats (1 mg/kg, s.c., 18-24 hr before the experiment) was dose-dependently antagonized by p-MPPI and p-MPPF with approximate ID50 of 3 and 0.7 mg/kg, respectively. p-MPPI also antagonized forepaw treading induced by 5-methoxy-N,N,-dimethyltryptamine (5-MeODMT) (5 mg/kg) and this antagonism was competitively overcome by higher doses of 5-methoxy-N,N,-dimethyltryptamine. p-MPPI and p-MPPF were able to antagonize the 8-OH-DPAT-(0.5 mg/kg) induced reduction in the 5-HIAA/5-HT ratio, a measure of 5-HT turnover in the hippocampus or striatum. No hypothermia or reciprocal forepaw treading was produced by either drug when given at doses as high as 10 mg/kg. Neither p-MPPI nor p-MPPF (10 mg/kg) given alone significantly altered the ratio of 5-HIAA/5-HT in the hippocampus or striatum. Also, binding of [3H]p-MPPF to hippocampal membranes was unaltered by the addition of 100 microM guanylyl-imidodiphosphate to the incubation medium. In conclusion, p-MPPI and p-MPPF behave, in vivo, as competitive antagonists of both postsynaptic 5-HT1A receptors and somatodendritic 5-HT1A autoreceptors.
Thielen
R J
RJ
Department of Pharmacology, University of Texas Health Science Center at San Antonio, USA.
Fangon
N B
NB
Frazer
A
A
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000037:antagonists & inhibitors; D000631:Aminopyridines / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D017660:Autoreceptors / Q000187:drug effects; D001831:Body Temperature / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006897:Hydroxyindoleacetic Acid / Q000032:analysis; D008297:Male; D010879:Piperazines / Q000378:metabolism / Q000494:pharmacology*; D011187:Posture; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000032:analysis; D012702:Serotonin Antagonists / Q000494:pharmacology*
D000631:Aminopyridines; D017660:Autoreceptors; D010879:Piperazines; D012702:Serotonin Antagonists; C087205:4-(2'-methoxyphenyl)-1-(2'-(N-(2''-pyridinyl)-4-iodobenzamido)ethyl)piperazine; D012701:Serotonin; D006165:Guanylyl Imidodiphosphate; D006897:Hydroxyindoleacetic Acid; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C099463:4-(2' methoxyphenyl)-1-(2'-(N-(2''-pyridinyl)-4-fluorobenzamido)ethyl)piperazine