ABSTRACT
The effect of extracts and constituents of St. John's wort, Hypericum perforatum, at various CNS receptors were studied by radioligand binding techniques in order to determine a profile of pharmacological activity in vitro. Binding inhibition was examined for the G-protein coupled opioid, serotonin (5-HT), histamine, neurokinin and corticotropin releasing factor (CRF) receptors, for the steroid estrogen-alpha receptor and for the ligand-gated ionchannel GABA(A) receptor. Hypericin showed the most potent binding inhibiton of all tested constituents to human CRF1 receptor with an IC50 value of 300 nM. Preliminary GTPgamma35S binding studies to CRF1 coupled G-protein indicated an antagonistic action for hypericin. The acylphloroglucinole hyperforin failed to inhibit 125I-astressin binding to hCRF, receptor up to 10 microM. Hyperforin inhibited binding to opioid and serotonin (5-HT) receptors at IC50 values between 0.4 and 3 microM, while hypericin and pseudohypericin inhibited with weaker potency. The biflavonoid I3,II8-biapigenin inhibited 3H-estradiol binding to the estrogen-alpha receptor with an IC50 value of 1 microM. The inhibition of 3H-muscimol binding to the GABA(A) receptor is likely to be exclusively due to GABA present in the extract. We therefore hypothesize that additive or synergistic actions of several ditsinct compounds may be responsible for the beneficial antidepressant effect of St. John's wort.
Subject(s)
Cerebellum/chemistry , Cerebellum/drug effects , Hypericum , Plant Extracts/pharmacology , Animals , Cerebellum/metabolism , Female , GTP-Binding Proteins/metabolism , In Vitro Techniques , Male , Radioligand Assay , Rats , Rats, Wistar , Receptors, Corticotropin-Releasing Hormone/metabolism , Receptors, Estrogen/metabolism , Receptors, GABA-A/metabolism , Receptors, Histamine/metabolism , Receptors, Metabotropic Glutamate/metabolism , Receptors, Neurokinin-1/metabolism , Receptors, Serotonin/metabolismABSTRACT
In vitro shoot regeneration from sterile leaf and petiole explants and from in-situ-collected inflorescence buds of Petasites hybridus was achieved by a simple two-step protocol. Murashige and Skoog (MS) nutrient medium was supplemented with 17.6 µM benzyladenine (BA)+0.54 µM naphthaleneacetic acid (NAA) to induce shoots. After 5 weeks of culture, 40% of the petiole and 27% of the leaf explants produced shoots compared to 76% of the inflorescence buds. Single shoots were excised and subcultured on MS medium supplemented with various cytokinins (N6-(Δ2-isopentenyl)adenine, BA, kinetin and thidiazuron). A concentration of 8.8 µM kinetin+0.54 µM NAA performed best in terms of shoot multiplication rate, average shoot length and spontaneous root induction.