Abstract
Objective To describe and to characterize the relaxing effect of an extract of the bark of Combretum leprosum on isolated arterial rings from different animals.Methods Rings (3 to 4mm) from rabbit, rat, or porcine arteries rings were suspended in an organ bath (Krebs, 37°C, 95%O2/5%CO2) to record isometric contractions. After the stabilization period (2 to 3 hours) contractions were induced by the addition of phenylephrine (0.1 to 0.3µM) or U46619 (10 to 100nM), and Combretum leprosum extract was added on the plateau of the contractions. Experiments were performed to determine the potency, duration, reversibility, and to get insights on the potential mechanism involved in extract-induced relaxations.Results In all rings tested, Combretumleprosum extract (1.5μg/mL) was able to cause relaxations, which were strictly endothelium-dependent. In rabbit or rat thoracic aorta rings, the relaxations were reversed by vitamin B12a or L-NG-nitroarginine. In porcine right coronary arteries and rabbit abdominal aorta, extract caused both L-NG-nitroarginine-sensitive and L-NG-nitroarginine-resistant relaxations. In rabbit thoracic aorta, the extract was relatively potent (EC50=0.20µg/mL) and caused relaxations; intriguingly the endothelium continued to produce relaxing factors for a long period after removing the extract. The magnitude of extract-induced relaxations was significantly reduced in the absence of extracellular Ca2+; in addition, the TRPs channels blocker ruthenium red (10µM) was able to revert extract-induced relaxations. Phytochemical analyses indicated that the extract was rich in polyphenol-like reacting substances.Conclusions Combretum leprosum extract contains bioactive compounds capable of promoting Ca2+-dependent stimulation of endothelial cells which results in a prolonged production of relaxing factors.
Highlights
Combretum leprosum Mart. (Combretaceae) is a shrub or small tree that grows in northeastern Brazil where it is known as mufumbo, mofumbo, cipoaba and pente-demacaco
extract of Combretum leprosum (ECL)-induced relaxation could be due to a direct action on the smooth muscle cells or to an indirect action mediated by the endothelium as is well established for ACh and other agents.[5]. To distinguish between these alternatives, the effect of ECL was determined in rabbit thoracic aorta rings containing endothelium or in rings in which the endothelium had been removed, as can be observed in figure 1C
1.77μg/mL, respectively.[17,18] Substances identified in other Combretum genera members are capable of inducing endothelium-dependent relaxation (EDR) in rat aortas; the concentrations required are higher than those of ECL; for example, 5 to 80μg/mL and EC50 of 3.9μg/mL and 9.5μg/mL for methanolic extract of C. celastroides leaves, and C. racemosum roots respectively.[3,4] As in the rat aorta, 1.5μg/mL of ECL causes complete relaxation of PE-induced contractions the vasodilator in the extract of compounds present in ECL are unlikely to be related to those already described in other members of the genus Combretum
Summary
Combretum leprosum Mart. (Combretaceae) is a shrub or small tree that grows in northeastern Brazil where it is known as mufumbo, mofumbo, cipoaba and pente-demacaco. Endothelial cells exhibit remarkable heterogeneity in responsiveness to agents that induce EDR either of homologous arteries from different animals species or of arteries from different vascular beds from the same animal; e.g acetylcholine (ACh), but not bradykinin (BK), induces EDR in the rabbit and rat aorta;(5,6) histamine causes EDR in rat aorta but not in rabbit aorta. It is highly recommended when describing the EDR of a new drug or natural product to examine its effects in same artery from more than one animal species and in different arteries from the same animal
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