Serotonin (5-HT)3 receptor blocking activities of YM060, a novel 4,5,6,7-tetrahydrobenzimidazole derivative, and its enantiomer in anesthetized rats.
YM060 [(R)-5-[(1-methyl-3-indolyl)carbonyl]-4,5,6,7-tetrahydro-1H-benzimida zol e hydrochloride], is structurally independent of other 5-HT3 receptor antagonists. We investigated in vivo 5-HT3 receptor blocking activity of YM060 and compared results with those of its enantiomer (S-form), ondansetron (GR38032F), granisetron (BRL43694), ICS205-930 [(3 alpha-tropanyl)-1H-indole-3-carboxylic acid ester], LY277359 [endo-5-chloro-2,3-dihydro-2,2-dimethyl-N-(8-methyl-8-azabicyclo[3.2.1] oct-3-yl)-7-benzofuran-carboxamide-(Z)-2-butenedioate (1:1)], Y25130 [(+-)-N-(1-azabicyclo[2.2.2]oct-3-yl)-6-chloro-4-methyl-3-oxo-3,4- dihydro-2H-1,4-benzoxazine-8-carboxamide hydrochloride] and zacopride [(R,S)4-amino-N-[1-azabicyclo (2.2.2)oct-3-yl]-5-chloro-2-methoxybenzamide(E)-2-butenedioat e]. YM060 injected i.v. dose-dependently inhibited the reduction in heart rate induced by 5-HT (30 micrograms/kg i.v.) in rats (von Bezold-Jarisch reflex) with an ED50 value of 0.036 (0.031-0.041) micrograms/kg (n = 3-5). Based on these values, YM060 was 53, 18, 23, 16, 11 and 4 times as potent as ondansetron, granisetron, ICS205-930, LY277359, Y25130 and zacopride, respectively. The S-form of YM060 also inhibited 5-HT-induced bradycardia, but with a potency approximately 250 times less than that of YM060 (R-form). YM060 dosed p.o. also inhibited 5-HT-induced bradycardia with an ED50 value of 0.59 (0.44-0.80) micrograms/kg (n = 3-5), indicating the drug to be 387, 66, 97, 6 and 16 times more potent than ondansetron, granisetron, ICS205-930, LY277359 and Y25130, respectively, but 2 times less potent than zacopride. Bioavailability of YM060 based on the p.o.-to-i.v. ED50 ratio (p.o./i.v. = 16) was lower than those of zacopride (2) and LY277359 (6), similar to that of Y25130 (22) and better than those of ondansetron (109), granisetron (60) and ICS205-930 (71).(ABSTRACT TRUNCATED AT 250 WORDS)
Miyata
K
K
Medicinal Research Laboratories I, Yamanouchi Pharmaceutical Co. Ltd., Ibaraki, Japan.
Kamato
T
T
Yamano
M
M
Nishida
A
A
Ito
H
H
Katsuyama
Y
Y
Yuki
H
H
Tsutsumi
R
R
Ohta
M
M
Takeda
M
M
D000284:Administration, Oral; D000818:Animals; D001562:Benzimidazoles / Q000493:pharmacokinetics / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D006339:Heart Rate / Q000187:drug effects; D007275:Injections, Intravenous; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D012702:Serotonin Antagonists; D013237:Stereoisomerism
D001562:Benzimidazoles; D012702:Serotonin Antagonists; D012701:Serotonin; C045918:2-methyl-5-HT; C071315:ramosetron