Orthosiphon stamineus Benth. (Lamiaceae) or Misai Kucing is a medicinal plant grown in Southeast Asia particularly Malaysia
and Indonesia. The leaves of the plant have been used for treatment of a wide range of ailments including diabetes,
hypertension, gout and cancer. This study aims to investigate the anti-hypertension effect of standardized ethanolic extract of O.
stamineus (OS-E) using in vitro and in vivo models. The in vitro anti-hypertensive effect was determined based on inhibitory
effect on angiotensin converting enzyme (ACE) activity as a marker for anti-hypertension. However, the in vivo
antihypertensive effect was investigated after oral administration of the extract on spontaneous hypertensive rats (SHR). The
systolic blood pressure was measured before and after 14-days treatment by the tail cuff method. Ethanolic extract of O.
stamineus was standardized based on the primary and secondary metabolites using HPLC, FT-IR, UV-VIS and gravimetric
methods. In vitro testing showed modest inhibition of the ACE activity by 22.1%, and the in vivo results in SHR rats showed
significant reduction in the systolic blood pressure in 4 out of 6 treated rats after treatment period for 14 days. In conclusion,
our preliminary results show blood pressure lowering effect of the OS-E extract which needs further investigation to explore the
extract’s mechanism of action.