Hypertension remains a major global health challenge and a significant risk factor for cardiovascular diseases. Its pathophysiology is multifactorial, involving endothelial dysfunction, renin–angiotensin–aldosterone system (RAAS) activation, and sympathetic nervous system overactivity. Current pharmacological interventions often target single pathways and may pose side effects with long-term use. Psychotria luzoniensis, an endemic Philippine plant, has previously demonstrated ACE inhibitory activity in vitro, but it’s in vivo antihypertensive potential and mechanistic pathways remain unexplored.

This study aimed to evaluate the antihypertensive effects and safety profile of the aqueous fraction of Psychotria luzoniensis leaves using a nitric oxide-deficient hypertensive mouse model. Specifically, it sought to:

1. Assess in vitro ACE inhibition activity

2. Determine in vivo modulation of ACE1, eNOS, and DBH

3. Conduct LC-QTOF-MS metabolite profiling

4. Evaluate acute oral toxicity and histopathological effects

Early hypertension was induced in mice using L-NAME (40 mg/kg) for 14 days alongside treatment with aqueous P. luzoniensis leaf extract at 30 mg/kg and 300 mg/kg doses (PLA30 and PLA300). LC-QTOF-MS was performed to identify bioactive metabolites. In vitro ACE inhibition assays were conducted spectrophotometrically. Enzyme-linked immunosorbent assays (ELISA) quantified ACE1, eNOS, and DBH levels in serum and tissue samples. Acute toxicity was assessed at 2000 mg/kg following OECD Guideline 423, with gross and histological evaluation of major organs. 

PLA300 significantly enhanced eNOS activity, reduced ACE1 expression, and suppressed DBH activity in a dose-dependent manner compared to PLA30. LC-QTOF-MS profiling identified flavonoids such as quercetin, kaempferol, rutin, hyperin, and glycosylated phenolics alongside with other less commonly reported metabolites. No mortality or observable organ damage was noted at the 2000 mg/kg dose, suggesting a favorable safety profile.

The aqueous leaf fraction of P. luzoniensis demonstrated antihypertensive effects through multiple mechanisms, including enhancement of endothelial function via eNOS activation, suppression of the renin–angiotensin–aldosterone system (RAAS) through ACE1 inhibition, and attenuation of sympathetic activity via DBH downregulation. These multi-target effects, together with preliminary safety findings, support the therapeutic potential of P. luzoniensis in the management of hypertension. Further studies are warranted to isolate and characterize active constituents and to validate long-term efficacy using chronic hypertension models.