Pharmacological basis for the empirical use of Eugenia uniflora L. (Myrtaceae) as antihypertensive.

The rational basis for the use of Eugenia uniflora L. (Myrtaceae) as antihypertensive in Northeastern Argentina was assessed in normotensive rats. Intraperitoneal administration of the aqueous crude extract (ACE) decreased blood pressure (BP) of normotensive rats dose-dependently until 47.1 +/- 8.2% of control. The effective-dose 50 was 3.1 +/- 0.4 mg dried leaves/kg (d.l./kg) (yielding of ACE: 17% w/w). To determine the origin of hypotensive activity. Alpha-adrenergic antagonistic and vasorelaxant ACE activities were tested. The dose-response curve for phenylephrine on BP was inhibited non-competitively until 80% of its maximal effect (at 8 mg d.l. ACE/kg). Perfusion pressure (PP) of rat hindquarters (previously vasoconstricted by high-K+) was decreased by ACE in a concentration-dependent manner until -32.3 +/- 11.5% of tonic contraction at 1.2 g d.l. ACE/100 ml. In addition, A.C.E demonstrated diuretic activity at a dose (120 mg d.l./kg) higher than the hypotensive one. It was almost as potent as amiloride, but while amiloride induced loss of Na+ and saving of K+, ACE induced decrease in Na+ excretion. The results suggest that the empirical use of Eugenia uniflora L. (Myrtaceae) is mostly due to a hypotensive effect mediated by a direct vasodilating activity, and to a weak diuretic effect that could be related to an increase in renal blood flow.