tokens: In brain membranes from spontaneously hypertensive rats clonidine , 10 ( - 8 ) to 10 ( - 5 ) M , did not influence stereoselective binding of [ 3H ] - naloxone ( 8 nM ) , and naloxone , 10 ( - 8 ) to 10 ( - 4 ) M , did not influence clonidine - suppressible binding of [ 3H ] - dihydroergocryptine ( 1 nM ) .