Alverine citrate is a 5-HT1A receptor antagonist, with an IC50 of 101 nM.
Alverine is a drug used for functional gastrointestinal disorders. Alverine acts directly on the muscle in the gut, causing it to relax. Alverine Citrate (20 mg/kg) suppresses the effect of 5-HTP, but not that of 8-OH-DPAT. However, when injected intracerebroventricularly (75 μg/rat) alverine citrate reduces 8-OH-DPAT-induced enhancement of rectal distension-induced abdominal contractions. In-vitro binding studies reveal that Alverine citrate has a high affinity for 5-HT1A receptors and a weak affinity for 5-HT3 and 5-HT4 subtypes[1]. Alverine may increase Ca influx during action potentials due to inhibition of the inactivation of L-type Ca channels, but may also suppress evoked activity by inhibiting the sensitivity of contractile proteins to Ca2+[2].
References:
[1]. Coelho, A.M., et al., Rectal antinociceptive properties of alverine citrate are linked to antagonism at the 5-HT1A receptor subtype. J Pharm Pharmacol, 2001. 53(10): p. 1419-26.
[2]. Hayase, M., et al., Evolving mechanisms of action of alverine citrate on phasic smooth muscles. Br J Pharmacol, 2007. 152(8): p. 1228-38.