Black cohosh acts as a mixed competitive ligand and partial agonist of the serotonin receptor.
Level 5 - mechanism / opinion, no new human data
Preclinical in vivo animal bioassay and in vitro cell culture study without human data
PubMed 12952416 · doi:10.1021/jf034264r
What was done
Researchers evaluated black cohosh (Actaea racemosa) rhizome extracts for potential estrogenic and serotonergic mechanisms. In vivo, ovariectomized Sprague-Dawley rats received a 40% 2-propanol extract (4, 40, and 400 mg/kg/day) by gavage for 2 weeks with or without 17beta-estradiol (50 microg/kg/day) to assess changes in uterine weight and vaginal cellular cornification. In vitro, extracts were screened against 10 recombinant human serotonin (5-HT) receptor subtypes via radioligand binding, followed by quantitative binding assays for 5-HT1A and 5-HT7 receptors and functional cAMP measurement in 5-HT7-transfected HEK 293T cells.
What was found
Black cohosh alone or combined with estradiol produced no changes in uterine weight or vaginal cellular cornification in ovariectomized rats. In receptor binding assays, the extract exhibited strong binding to 5-HT1A, 5-HT1D, and 5-HT7 subtypes. The 40% 2-propanol extract inhibited radioligand binding at the human 5-HT7 receptor with an IC50 of 2.4 +/- 0.4 microg/mL and at the rat 5-HT1A receptor with an IC50 of 13.9 +/- 0.6 microg/mL. In transfected HEK cells, a methanol extract acted as a mixed competitive ligand and increased cAMP levels—indicating partial agonism at 5-HT7—which was blocked by the antagonist methiothepin.
Why it matters
These findings suggest that black cohosh does not act via classic peripheral estrogenic pathways, pointing instead to central serotonergic receptor modulation as a candidate mechanism for hot flash reduction.
Limits
This study was strictly preclinical, relying on cell culture and ovariectomized rodent models with no human clinical testing. The abstract does not report the number of rats used, physiological brain concentrations, or the isolation of specific active phytochemical constituents.
Cited by
- context Clinical studies show black cohosh acts on serotonin and dopamine pathways in the hypothalamus to aid in temperature regulation and mood.