Biological Activity
A potent and highly selective 5-HT 4 partial agonist, with pK i values of 8.7 at 5-HT 4 sites in guinea pig striatum and > 6 at various other receptors, including 5-HT 1A , 1D , 2A , 2C , D 1 , D 2 and M 1-3 . Active in vivo , with an intrinsic activity relative to 5-HT of 0.5.
Biochem/physiol Actions
RS 67333 is a selective, high affinity (pKi = 8.7 for the 5-HT4 binding site in guinea-pig striatum) partial agonist toward 5-HT4 receptor that relaxes carbachol-contracted rat oesphageal muscularis mucosae ex vivo (pEC50/%reversal = 8.7/50 with RS 67333 vs. 8.2/100 with 5-HT) and induces tachycardia (tachyarrhythmia) of anaesthetized micropigs in vivo (ED50 via i.p. in μg/kg over max heart rate increase in beats/min = 4.9/35 with RS 67333 vs. 3.2/95 with 5-HT). RS 67333 is also reported to show high affinity for sigma receptors (pKi = 8.9/σ1 and 8.0/σ2), while exhibiting much reduced affinity toward a panel of other receptors, including 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3 (pKi <6.4), muscarinic receptors (pKi = 5.2/M1 & 5.3/M2), and adrenoceptors (pKi <6.7 for α1A, α1B, α2A, α2B, β1, β2).
