Antagonism by Phentolamine and Yohimbine not Hydralazine on Noradrenaline-Induced Hypertension in Rat

Abstract

Noradrenaline (10 mcg, IV) increases blood pressure of anaesthetized rats with little effect on heart rate. Pretreatment of the rat with hydralazine (2 mg/kg IV) could not inhibit the noradrenaline-induced hypertension in the rats. Both phentolamine (2 mg/kg IV) and yohimbine (0.25 mg/kg IV) not only reduce the blood pressure of anaesthetized rats significanlly (p ≤ 0.05) but also inhibits /lie hypertensive effect of noradrenaline (10 mcg, IV). Phentolamine (2 mg/kg IV), neither hydralazine nor yohimbine pretreatment, significantly decreased the heart rate of the anaesthetized rats (p ≤ 0.05) from the predrug value. The findings suggest, therefore, that hydralazine is not suitable for the treatment of noradrenaline-induced hypertension.