Estudo da ação cardiovascular do extrato aquoso e da fração butanólica padronizados de folhas de Piper aduncum L. de Manaus, AM.

Abstract

Piper aduncum (Piperaceae), native in the Amazonian Region, is known as pimenta-de-macaco and aperta ruão. It is popularly used to treat hemorrhage, hemorrhoids, diarrhea, tooth pain and inflammation. Phytochemical studies relate the isolation and identification of more than 47 compounds from P. aduncum; dilapiol (phenylpropanoid) is the main compound. However, pharmacological studies with standardized extracts and isolated compounds are scarce and there are no scientific paper showing a quantitative chemical standardization of Piper aduncum extracts. Considering these information, the goal of this project was to investigate the pharmacodynamics and the cardiovascular effects of P. aduncum standardized extracts in rodents. Plant leaves were collected at Federal University of Amazonas – UFAM. The infusion of the dried powdered leaves originated the aqueous extract (AE), which after partition in butanol yielded the butanolic fraction (BuF). AE and BuF standardized in HPLC-UV 260 nm showed 9 major peaks with characteristic retention times and peak amplitudes. BuF was purified in preparative HPLC, yielding 6 fractions (F1 to F6). Pharmacological studies showed that mice orally treated with AE (1 g/kg) did not show any different effect comparatively to the control water treated animals; BuF intraperitoneally injected (0.2 and 0.5 g/kg) caused slight sedation and quietness in the first 2 h after treatment. In anesthetized rats, i.v. injection of AE (1, 3 and 10 mg/mL) produced dose related hypertension. Previous treatment with prazosin (1 mg/kg, i.v.) inverted the AE effect to hypotension, which was blocked and reverted again to hypertension after injection of propranolol. In control conditions, adrenaline injection (ADR 0.1, 0.3 and 1.0 μg/mL) produced a biphasic effect (hypertension and hypotension), dependent on the injected dose and AE (1, 3 and 10 mg/mL) produced hypertension. After prazosin treatment, ADR and AE both produced hypotension which was reverted to hypertension after propranolol treatment. In isolated rat left atria, incubation of either AE or BuF increased the contraction force; the effect was blocked by propranolol (10-6 M), indicating a positive inotropic effect mediated by β1-adrenergic receptors. In rat isolated right atrium, AE and BuF increased the heart rate, but the Ca2+-ATPase enzyme activity in vitro was not inhibited by BuF. In rat vas deferens, BuF inhibited noradrenaline maximal contraction by 35%; EC50 was not changed, showing a non-competitive antagonistic interaction and excluding a α-adrenergic blockade by the plant extracts. Similarly, in the rat vas deferens pre-contracted with ATP, incubation of BuF inhibited the effect of ATP on purinergic P1 receptors. In electrically stimulated vas deferens, BuF inhibited the contraction amplitude by 60%, suggesting either a L-type calcium channel blockade or a local anesthetic effect on the sympathetic nerve terminals. On rat uterus cell cultures and cardiomyocytes cells, however, the calcium influx was not changed by BuF incubation. The results show that the AE of P. aduncum may produce hypertension by α1-adrenergic receptor activation, may produce hypotension by β2-adrenoceptor activation and tachycardia plus positive inotropic effect by β1-receptor activation. The data indicate that the AE may contain adrenaline, or a compound with the same pharmacological activity, which might produce vasoconstriction to interrupt bleeding, as mentioned in folk use.