Effects of dl-norephedrine and its enantiomers on norepinephrine uptake and release in isolated rat caudal artery.

Racemic norephedrine (dl-NOR), is a phenylethylamine derivative that is pharmacologically classified as a mixed-acting sympathomimetic amine. It is the active ingredient in many over-the-counter nasal decongestants and diet aid products. This research project was performed to examine the effects of dl-NOR and constituent enantiomers on the uptake and release of tritiated norepinephrine (3H-NE) in vascular tissue. All three NOR species significantly inhibited the uptake of 3H-NE into the isolated caudal artery of male Sprague-Dawley rats (p < 0.01). There was no significant difference in potency between either d- or l-NOR for this effect. There was, however, no effect of any NOR species on 3H-NE release, not even at concentrations which effectively inhibited uptake. These results indicate that inhibition of NE reuptake may be a component of the mechanism of action of NOR, but that a displacement of NE from neuronal storage sites is not. However, because the vasoactive effects of NOR have been shown to be mediated almost exclusively through the l-enantiomer, the lack of stereoselectivity in the current study indicates that the blockade of NE uptake by NOR is only a minor component of its vasoactive properties.