Antihypertensive Effect of Boysenberry Seed Polyphenols on Spontaneously Hypertensive Rats and Identification of Orally Absorbable Proanthocyanidins with Vasorelaxant Activity

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The antihypertensive effect of a single oral administration of a boysenberry seed polyphenol extract to spontaneously hypertensive rats was evaluated at different doses (100 and 200 mg/kg), and a significant decrease in systolic blood pressure (SBP) was observed up to 6 h post administration. The extract was separated into proanthocyanidin-rich and ellagitannin fractions by solvent partition. A significant decrease in SBP was observed only after administering the proanthocyanidin-rich fraction, and this decrease was abolished by an N ^G-nitro-L-arginine methyl ester (L-NAME) injection. An analysis of the orally absorbable components showed that intact dimeric and trimeric procyanidins and propelargonidins were detectable in the plasma with a maximal concentration 2 h post administration. The vasorelaxant activity of the extract was also confirmed by in vitro assay using rat aorta rings. These results suggest that proanthocyanidins (PAs) in boysenberry seeds may have played an important role in the observed antihypertensive effect.