AJP - Heart and Circulatory Physiology, Vol 234, Issue 3 235-H243, Copyright © 1978 by American Physiological Society
Norepinephrine metabolism in canine saphenous vein: prevalence of glycol metabolites
S. M. Muldoon, P. M. Vanhoutte and G. M. Tyce
To examine the disposition of [3H]norepinephrine ([3H]NE) in adrenergically
innervated veins, helical strips of canine saphenous veins were incubated
in Krebs-Ringer solution containing D,L[3H]NE (2 X 10(-7) M) for 2 h.
[3H]NE and its metabolites were measured in extracts of veins and in
superfusate (Krebs-Ringer) collected during basal conditions and during
release of [3H]NE evoked by electrical stimulation (1-8 Hz), tyramine (5 X
10(-6) to 5 X 10(-4) M), or high concentrations of potassium (35-100
meq/liter). During basal conditions, the efflux from veins comprised mainly
metabolits of [3H]NE, especially 3,4-dihydroxphenylglycol (DOPEG) and
3-methoxy-4-hydroxyphenylglycol (MOPEG); this pattern was unchanged by
cocaine treatment, and monoamine oxidase inhibition reduced the formation
of DOPEG. During evoked release of NE, the major metabolites in the
perfusate were DOPEG, MOPEG, and normetanephrine, and their proportions
differed with the stimulus used: O-methylated metabolites in the perfusate
always increased more than did the deaminated catechol compounds; DOPEG and
MOPEG were released in greater amounts than the corresponding acids; and
cocaine treatment caused a higher content of all metabolites except DOPEG.
3-Methoxy-4-hydroxymandelic acid was also formed by the vein but was
retained in the tissue.
