Pharmacological evidence of α2-adrenergic receptors in the hypotensive effect of Platonia insignis mart.

Platonia insignis Mart. (Clusiaceae) is a medicinal plant from the Brazilian Amazon region. The present study evaluated the biological potential of the ethanol extract (Pi-EtOH) and ethyl acetate fraction (Pi-EtOAc) of the P. insignis fruit shells on the cardiovascular system of rats. Pi-EtOH or Pi-EtOAc (12.5, 25, and 50 mg/kg) was administered intravenously in normotensive rats (260-300 g), and the mean arterial pressure and the heart rate were monitored. The Pi-EtOH induced hypotension (-11.56±0.89, -7.43±0.85, and -17.56±1.97 mmHg) followed by bradycardia in two highest doses (-8.89±3.62 and -15.79±1.83 beats/min) and Pi-EtOAc, at the same doses, induced hypotension (-11.2±1.03, -14.48±1.13, -29.89±2.67 mmHg) more intensively, followed by tachycardia at the dose 12.5 and 25 mg/kg (15.64±2.06, 19.31±1.92 beats/min) and bradycardia at a dose of 50 mg/kg (-9.98±7.33 beats/min). The hypotensive response from Pi-EtOAc was not attenuated when used in the pretreatment with L-NAME, verapamil, propranolol, and hexamethonium. However, when using yohimbine, the hypotensive effect was inhibited (-4.42±1.28 (P<.05), -3.29±0.99 (P<.05), 2.06±1.18 mmHg (P<.05); Student's t-test). Hence, the Pi-EtOAc seems to act similarly to the α2-adrenergic agonist in this hypotensive effect.

Antihypertensive and vasorelaxant effects of ethanol extract of stem barks from Zanthoxylum rhoifolium Lam. in rats.

Administration of ethanol extract of stem bark from Z. rhoifolium (EEtOH-ZR) induced hypotension associated with a dual effect in heart rate in normotensive rats. This response was highlighted in spontaneously hypertensive rats (SHR). In rat superior mesenteric artery rings, the cumulative addition of EEtOH-ZR (0.1-750 microg/mL) on a phenylephrine-induced pre-contraction (10(-5) M) promoted a vasorelaxant effect by a concentration-dependent manner and independent of vascular endothelium. A similar effect was obtained on KCl-induced pre-contractions (80 mM). EEtOH-ZR attenuated contractions induced by cumulative addition of CaCl2 (10(-6)-3 x 10(-2) M) in depolarizing medium without Ca2+ only at 500 or 750 microg/mL. Likewise, on S-(-)-Bay K 8644-induced pre-contractions (10(-7) M), the EEtOH-ZR-induced vasorelaxant effect was attenuated. EEtOH-ZR (27, 81, 243 or 500 microg/mL) inhibited contractions induced by cumulative addition of phenylephrine (10(-9) - 10(-5) M) in endothelium-denuded preparations or by a single concentration (10(-5) M) in a Ca(2+)-free medium. The involvement of K+ channels was evaluated by tetraethylammonium (3 mM); the EEtOH-ZR-induced vasorelaxation was not attenuated. Thus, calcium influx blockade through voltage-operated calcium channels (CavL) and inhibition of calcium release from intracellular stores are probably underlying EEtOH-ZR-induced cardiovascular effects.