Angiotensin I-converting enzyme inhibitor activity of nutritive plants in KwaZulu-Natal

Traditional herbal remedies still form an integral part of South African culture, hence necessitating reports on the scientific rationale for their uses. Organic and aqueous extracts from 16 nutritive plants found in KwaZulu-Natal, South Africa were screened for angiotensin I-converting enzyme (ACE) inhibitory activity using a fluorometric enzyme assay. A plant was considered to have potential antihypertensive properties if it inhibited the ACE enzyme and thus the conversion of angiotensin I to angiotensin II by greater than 50%. Eight of the 16 plants screened demonstrated ACE inhibitory activity and satisfied these criteria. These eight plants were then subjected to a gelatin salt block test for tannins to show that the ACE inhibitory activities were not due to the presence of tannins, as tannins also inhibit ACE activity. The plants that showed ACE inhibitory activity were Amaranthus dubius, Amaranthus hybridus, Asystasia gangetica, Galinsoga parviflora, Justicia flava, Oxygonum sinuatum, Physalis viscosa, and Tulbaghia violacea. T. violacea in particular shows promise with regards to ACE inhibition as in vivo administration of this extract showed only a 2.2% increase in maximum mean arterial pressure when compared to the 14.5% increase observed in the control group after co-administration with exogenous Ang I.