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Steric aspects of adrenergic drugs. XXII. Retention of (+)- and (-)- 14 C-norepinephrine by mouse heart.

After intravenous infusion (total dose 40 mcg./kg.) of the isomers of norepinephrine to normal or reserpine-pretreated mice, the initial accumulation by the heart was the same for both isomers. The injected isomers disappeared from the normal heart in a single exponential phase. The unnatural isomer disappeared faster, t1/2 2.5 hr., than the natural (-)-isomer, t1/2 7.6 hr. In mice pretreated with iproniazid, iproniazid and guanethidine, or iproniazid and α-methyl-p-tyrosine, the rate constants and the t1/2 values for the isomers were unaltered. The results indicate that retention, probably by storage vesicles, favors the natural isomer; hence, it is stereoselective. Reserpine, which inhibited the accumulation by storage vesicles, drastically reduced the accumulation of isomers, and the accumulated isomers disappeared at a similar rate constant with a t1/2 of approximately 1 hr. Racemic norepi-nephrine disappeared in two phases, each having a separate rate constant which approximate the values obtained with (+)- and (-)- norepinephrine. In the iproniazid-pretreated mice, injection of equal amounts of (-)- or (+)-14C-norepinephrine resulted in higher O-methylated products from the (+)-form.