Journal of Applied Physiology, Vol 51, Issue 5 1245-1250, Copyright © 1981 by American Physiological Society
Effects of norepinephrine and alpha-block on O2 uptake and blood flow in dog hindlimb
S. M. Cain and C. K. Chapler
Norepinephrine (NE) may increase skeletal muscle O2 demand at the same time
that it restricts O2 transport by vasoconstriction. We prevented
vasoconstriction with 3.0 mg/kg phenoxybenzamine (alpha-Bl) in 10
anesthetized, paralyzed dogs ventilated at constant rate. Hindlimb and
whole-body O2 uptake (VO2) and blood flow were measured for a 20-min
control period, 20 min of NE infusion at 1 micrograms . kg-1 . min-1 either
intravenously (iv) or intra-arterially (ia), and 20 min of recovery. The
sequence was repeated for the other route of infusion. A second group of 10
without alpha-Bl was treated the same. Cardiac output increased with both
ia and iv infusions in the no-block group and was unchanged in the alpha-Bl
group. Limb blood flow increased 25% during the first 5 min of iv but
decreased 40% with ia infusion in the no-block group. Whole-body VO2 was
significantly increased 9% in both groups by both routes of NE. Limb VO2
was significantly decreased in the no-block group at 5 min of NE infusion
iv when limb blood flow was increased. Limb VO2 did not change
significantly in the alpha-Bl group with NE by either route. Hindlimb
skeletal muscle did not participate in or contribute to the calorigenic
effect of NE on the whole body, and that lack of effect was not due to any
effect of NE on rate or distribution of blood flow in the limb.
