Hypotensive Principles of Uncaria Hooks

A methanol extract of the Oriental crude drug “chōtōkō”, Uncaria hooks, elicited a strong and long-lasting hypotension on injection into rats. The activity differed considerably from the effects expected for the known constituents, rhynchophylline and its analogues, which elicit only weak transient hypotensive effects. Fractionation of the extract, along with the pharmacological assays, resulted in isolation of three indole alkaloid glucosides, cadambine ( 1 ), 3α-dihydrocadambine ( 2 ) and 3β-isodihydrocadambine ( 3 ). The former ( 1 ) was found inactive but the latter two ( 2 and 3 ) exhibited strong and long-lasting hypotensive actions similar to the extract. 3β-Dihydrocadambine ( 4 ), which was not detected in the extract, also showed a strong hypotensive activity. Key Word Index Uncaria - Rubiaceae - Indole alkaloid glucoside - Cadambine - 3α-Dihydrocadambine - 3β-Isodihydrocadambine 1 Part 50 in the series on the validity of the Oriental medicines.