Journal of Applied Physiology, Vol 58, Issue 1 244-250, Copyright © 1985 by American Physiological Society
Compartmental analysis of the efflux of l-[3H]norepinephrine from isolated perfused rat lungs
P. J. Metting, J. A. Levin and J. T. Samuels
Isolated rat lungs, pretreated with 100 microM pargyline and 100 microM
U-0521 (3',4'-dihydroxy-2-methylpropriophenone) to block metabolism of
norepinephrine (NE), were perfused with 0.3 microM 3H-labeled
l-norepinephrine (1-[3H]-NE) for 30 min. Efflux samples were then collected
for 30 min during washout of the tissue with amine-free Krebs solution.
Compartmental analysis (nonlinear least-squares regression) of the efflux
of tissue l-[3H]NE content vs. time indicates that NE is accumulated in a
large slowly equilibrating compartment (t 1/2 = 58.15 +/- 6.84 min) in
addition to distribution in the vascular (blue dextran tracer) and
extracellular ([3H]sorbitol tracer) fluid compartments of the lung.
Pretreatment of the lungs with 100 microM cocaine hydrochloride reduces the
total l-[3H]NE space from 7.44 +/- 1.91 to 2.48 +/- 0.23 ml/g (P less than
0.05) by selectively decreasing the size of the slow NE compartment from
6.99 +/- 1.97 to 1.67 +/- 0.14 ml/g (P less than 0.05). The large size,
cocaine sensitivity, and long efflux half time of this compartment suggest
that neuronal uptake contributes to the pulmonary vascular inactivation of
l-[3H]NE.
