Effects of the enantiomers of 3-PPP on DA1 and DA2 dopamine receptors in the dog.

The (+)- and (-)-enantiomers of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP) were studied for their effects on DA1 and DA2 dopamine receptors in pentobarbital anesthetized dogs. 3-PPP enantiomers were administered into the renal artery after phenoxybenzamine pretreatment to determine possible DA1 activity; dopamine was also injected for comparison. DA2 activity was determined by injection of the enantiomers into the femoral vascular bed with intact nerve supply and without phenoxybenzamine; dipropyl dopamine (DPDA) or apomorphine were used as standard DA2 agonists. Antagonist activity of the enantiomers on DA1 or DA2 receptors was determined by simultaneous administration of the enantiomer with DA in the renal vascular bed and with DPDA or apomorphine in the femoral vascular bed. Neither enantiomer was active as a DA1 agonist, but both exhibited antagonist activity. Both enantiomers were found to be agonists of the DA2 receptor; in addition, both showed DA2 antagonist activity. In all actions the (-)-enantiomer was approximately 4 times more potent than the (+)-enantiomer.