AJP - Heart and Circulatory Physiology, Vol 243, Issue 5 732-H737, Copyright © 1982 by American Physiological Society
Metabolism of norepinephrine in vitro by dog pulmonary arterial endothelium
D. K. Rorie
The importance of endothelial cells in the removal of norepinephrine from
synaptic clefts in dog pulmonary artery was studied. Strips of artery cut
helically were denuded of endothelium by gently stroking the intimal
surface with a wooden applicator stick or were studied with endothelium
intact. All strips were prelabeled in L-[3H]norepinephrine (2 X 10(-7) M)
and mounted for superfusion. Superfusate was collected continuously before,
during, and after electrical stimulation (10 V, 2 ms, 2 Hz). Measurements
were made of the amounts of [3H]norepinephrine and its metabolites in
superfusate and in tissue. These studies have established that
3,4-dihydroxyphenylglycol is of neuronal origin and O-methylated
metabolites are of extraneuronal origin. The formation of extraneuronal
metabolites in smooth muscle and endothelium was examined by either
blocking uptake of norepinephrine into each, in turn, or by combining
blockade of uptakes with the elimination of access of norepinephrine to
endothelial tissue by completely removing it. Electrical stimulation
elicited the overflow of large amounts of norepinephrine,
3,4-dihydroxyphenylglycol, and O-methylated metabolites into superfusate in
strips with intact endothelium; in strips denuded of endothelium there were
striking decreases in the amounts of O-methylated metabolites produced.
These studies show that pulmonary arterial endothelium participates in the
extraneuronal metabolism of norepinephrine released by sympathetic nerve
stimulation.
