Hypotensive action of Nangapiry, a Paraguayan natural medicine, in rodents.

ABSTRACT

Hypotensive action mechanism of a cation exchange resin adsorbate (IR-120A) separated from a Paraguayan Natural Medicine, Nangapiry, was investigated. Blood pressures of normal and pithed rats and contractions of isolated thoracic aorta and atria of mice were measured. The blood pressure on normal rats was reduced by an intravenous injection of IR-120A (5 mg/kg). The hypotensive effect on the pithed rat appeared more lasting than that on normal rats by IR-120A. The IR-120A (100 microg-3 mg/ml) concentration-dependently depressed prostaglandin (PG) F2alpha (10 microM)- or KCl (40 mM)-induced aortic contractions and electrically-evoked contraction of left atria, and at a lesser extent spontaneous beating rate of right atria. The 50% inhibitory concentrations (IC50) for the PGF2alpha- and KCl-induced aortic contractions were 713 and 828 microg/ml, respectively, and the IC50 values for the muscle contraction and the beating rate were 1.04 and >3 mg/ml, respectively. These results suggest that the hypotensive action of IR-120A are peripherally elicited by the dilatation of artery and the depression of heart contraction, but not the reduction of heart rate.