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. [ABSTRACT FROM AUTHOR]