Animal experiment:

Mice[2]Naive, adult (7-12 week old) mice of outbred Swiss-Webster stock are used in all in vivo experiments. Mice are brought to a quiet testing room, and acclimated to table-top Plexiglas observation chambers (30 cm high; 30 cm diameter) for 30 min. They are then weighed and injected with Ginsenoside Rf (25, 50, or 75 mg/kg) or vehicle (preceded by naloxone or saline in one experiment). Twenty min later, a 0.9% solution of glacial acetic acid is injected intraperitoneally (i.p.) in a volume of 10 mL/kg. For the next 30 min, the number of constrictions (writhes)-strong contractions of the abdominal musculature accompanied by dorsoflexion of the back and extension of the hindlimbs-are counted and recorded in 5-min blocks. Four mice (one per chamber) are observed simultaneously by a single, experienced experimenter. To control for the considerable circadian and other environmental variance accompanying this nociceptive assay, two vehicle controls are tested alongside two Ginsenoside Rf-administered mice in every experimental session[2].

Ginsenoside Rf is a trace component of ginseng root. Ginsenoside Rf inhibits N-type Ca2+ channel.

Ginsenoside Rf is a saponin, which is present in only trace amounts within ginseng. At saturating concentrations, Ginsenoside Rf rapidly and reversibly inhibits N-type, and other high-threshold, Ca2+ channels in rat sensory neurons to the same degree as a maximal dose of opioids. The effect is dose-dependent (half-maximal inhibition: 40 μM) and it is virtually eliminated by pretreatment of the neurons with pertussis toxin, an inhibitor of G(o) and Gi GTP-binding proteins. Ginsenoside Rf also inhibits Ca2+ channels in the hybrid F-11 cell line[1].

Since inhibition of Ca2+ channels in sensory neurons contributes to antinociception by opioids, analgesic actions of Ginsenoside Rf are tested. Dose-dependent antinociception is found by systemic administration of Ginsenoside Rf in mice using two separate assays of tonic pain: in the acetic acid abdominal constriction test, the ED50 is 56±9 mg/kg, a concentration similar to those reported for aspirin and acetaminophen in the same assay; in the tonic phase of the biphasic formalin test, the ED50 is 129±32 mg/kg[2].

References:
[1]. Nah SY, et al. A trace component of ginseng that inhibits Ca2+ channels through a pertussis toxin-sensitive G protein. Proc Natl Acad Sci U S A. 1995 Sep 12;92(19):8739-43.
[2]. Mogil JS, et al. Ginsenoside Rf, a trace component of ginseng root, produces antinociception in mice. Brain Res. 1998 May 11;792(2):218-28.