Vasodilating activity is relevant to the antihypertensive effect
of oxindole alkaloids from Uncaria.3b With the exception of
compound 8, all other alkaloids were investigated for their relaxation
effects on KCl- or phenylephrine-induced contraction in rat thoracic
aorta rings (Table 2). Dihydrocorynantheine (9) exhibited significant
vasodilating activity against phenylephrine-induced contraction in
rat thoracic aorta rings (IC50 ) 6.73 μg/mL). In addition, macrophylline
A (2), isorhynchophylline (6), and 9 showed weak inhibitory action on KCl-induced contraction. The other compounds
were considered inactive, with IC50 > 30 μg/mL.