AJP - Heart and Circulatory Physiology, Vol 239, Issue 2 238-H246, Copyright © 1980 by American Physiological Society
Disposition of norepinephrine during nerve stimulation in dog saphenous vein
D. K. Rorie, S. M. Muldoon and G. M. Tyce
The relative importance of neuronal and extraneuronal uptake in the
disposition of norepinephrine (NE) released by electrical stimulation (ES)
from adrenergic nerves in isolated dog saphenous vein was determined.
Helical strips of vein were incubated in L-[7-(3)H]NE (1 x 10(-6)M) and
mounted for superfusion. Superfusate was collected continuously before,
during, and after ES (10 V; 2 ms; 1, 2, and 5 Hz). Measurements were made
of [3H]NE and its metabolites in vein and in superfusate. Previous studies
have established that 3,4-dihydroxyphenylglycol (DOPEG) is of neuronal
origin and O-methylated metabolites (OMM) are of extraneuronal origin.
Thus, extraneuronal uptake was estimated directly by measuring the amounts
of OMM in superfusate, and neuronal uptake followed by metabolism was
estimated by measuring [3H]DOPEG. The magnitude of the neuronal uptake
fraction that enters vesicles for reuse was estimated from the compensatory
increases in [3H]NE and in OMM when neuronal uptake was blocked. Similar
amounts of released NE were taken up by neuronal uptake, by extraneuronal
uptake, and diffused out of the synaptic cleft. Between 5-20% of the
released NE was sequestered in vesicles for reuse.
