Influence of l-stepholidine on blood pressure and its relation toα-adrenoceptors

Intravenous injection of l-stepholidine (SPD) 2.5 and 0.5 mg/kg lowered the blood pressure by 30±8% and 29±6% in anaesthetized dogs and rats respectively. This hypotensive action of SPD was antagonized by phentolamine 1 mg/kg or yohimine 1.25-5 mg/kg. However, SPD 0.5 and 2.5 mg/kg increased the blood pressure in reserpinized rats or dogs, which was antagonized by yohimbine 0.5-2 mg/kg, phenoxybenzamine 2.5-5 mg/kg or prazosin 1 mg/kg. SPD 5-50 mg/kg iv inhibited the pressor action induced by noradrenaline or clonidine, or reversed the pressor action induced by adrenaline.
These results indicated that the hypotensive action of SPD was mainly related to the stimulation on presynapticα2-adrenoceptor, while in large doses (more than 10-16 times for hypotensive dose), to block the postsynaptic α-adrenoceptors； its hypertensive action was related to the stimulation on postsynapticα2/α1 adrenoceptors.