Abstract
Isolated rabbit hearts were perfused with 200 ng/ml of l-or d-norepinephrine; the concentration in the effluent was determined fluorimetrically. Untreated hearts removed significantly less d-than l-norepinephrine from the perfusate. Pretreatment with reserpine (to impair granular uptake) reduced the removal of l-but not of d-norepinephrine; rate of removal was then equal for the two isomers. Pretreatment with pargyline (to block intraneuronal monoamine oxidase) reduced the removal of both isomers. Pretreatment with both reserpine and pargyline reduced removal of l-norepinephrine to very low levels but was not more effective against the d-isomer than pretreatment with pargyline alone. These results are consistent with the view that the rats of tranemembranal uptake is influenced by the intraneuronal concentration of the free amine. Thus, the inactivating mechanisms (i.e., granular uptake and monoamine oxidase), by influencing the intraneuronal concentration of the free amine, play an important role in determining the rats of transmembranal uptake. Because of the different intraneuronal fate of the two isomers of norepinephrine, removal from the perfusion fluid can (under appropriate experimental conditions) be greater for l-than for d-norepinephrinein spite of the fact that the transmembranal uptake mechanism of the rabbit heart is not stereospecific.
Footnotes
- Received May 18, 1970.
- Accepted July 20, 1970.
- © 1970 by The Williams & Wilkins Co.
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