Polyphenolic composition and hypotensive effects of parastrephia quadrangularis (Meyen) cabrera in rat

Parastrephia quadrangularis (Pq), commonly called “Tola”, is widely used in folk medicine in the Andes, including for altitude sickness. In this study, polyphenolic composition was determined, and hypotensive effects were measured; the ethnopharmacological use as hypotensive was related to the presence of phenolic compounds. For this purpose, male Sprague-Dawley rats (6 to 8 weeks of age, 160 to 190 g) were fed Pq extract (10 to 40 mg/kg) for 10 days through gavage. Blood pressures and heart rate were significantly (p < 0.01) reduced in normotensive rats receiving Pq extract (40 mg/kg body weight). Pq extract induced a negative inotropic effect, and endothelium-dependent vasodilation mediated by nitric oxide (NO). Furthermore, preincubation with Pq extract significantly decreased the cytosolic calcium on vascular smooth muscle cells A7r5 in response to L-phenylephrine (PE). Seven metabolites were isolated from the Pq extract, but three flavonoids (10⁻⁴ M) showed similar vasodilation to the extract in intact rat aorta as follows: 5,3^′,4^′-trihydroxy-7-methoxyflavanone (2); 3,5,4^′-trihydroxy-7,8,3^′-trimethoxyflavone (6); and 5,4^′-dihydroxy-3,7,8,3^′-tetramethoxyflavone (7). The Pq extract and compounds 2 and 7 significantly (p < 0.05) reduced the contraction to Bay K8644 (10 nM, an agonist of Ca_V1.2 channels). Administration of Pq decreased cardiac contractility and increased endothelium-dependent and-independent vasodilation.