Effect of a crude extract of Mandevilla velutina on contractions induced by bradykinin and [des-Arg9]-bradykinin in isolated vessels of the rabbit.

The effect of a crude aqueous/alcoholic extract of Mandevilla velutina on the contractile responses induced by bradykinin (Bk), [des-Arg9]-Bk and noradrenaline (NA) in rings of arterial and venous rabbit vessels was analysed. The contractile responses induced by Bk, [des-Arg9]-Bk differed between the rings of the aorta, jugular and mesenteric veins. Rings of the aorta and mesenteric vein were stimulated by both peptides, but were more sensitive to [des-Arg9]-Bk. The jugular vein was not only more sensitive to Bk but also did not respond to [des-Arg9]-Bk, even in the presence of a high concentration of this peptide. Pre-incubation for 20 min with the crude extract of mandevilla velutina rhizomes (1 mg ml-1) antagonized the contractions produced by both peptides. This blockade was surmountable by about a 10-30 fold increase in the concentration of both Bk and [des-Arg9]-Bk. In the aorta and mesenteric vein the NA-induced contractions were not affected by 1 mg ml-1 of the extract. Bk (1 to 100 nM) caused a concentration-related contractile response in rings of the rabbit jugular vein. Incubation for 20 min with the crude extract (0.25-1 mg ml-1) caused a concentration-dependent displacement to the right of the Bk concentration-response curves and depressed the maximal response. The onset of action of the crude extract was rapid and was reversible after intermittent washing of the preparations for 30-60 min. 6 These findings confirm and extend our previous work and indicate that the crude extract of Mandevilla velutina selectively antagonizes the action of Bk and related peptides on both B1- and B2-receptors present in rabbit vascular muscle.