AJP - Regulatory, Integrative and Comparative Physiology, Vol 248, Issue 4 400-R406, Copyright © 1985 by American Physiological Society
Blood pressure and norepinephrine spillover during propranolol infusion in humans
J. D. Best and J. B. Halter
To determine whether a reflex increase of sympathetic nervous system
activity contributes to maintenance of blood pressure during acute
beta-adrenergic blockade, we measured plasma norepinephrine levels and
norepinephrine kinetics during propranolol administration. During a 90-min
infusion of propranolol (10 mg iv + 80 micrograms/min) in 12 normal
subjects, heart rate fell from 56 +/- 2 to 49 +/- 2 (SE) beats/min (P less
than 0.001), but there was no fall in mean arterial blood pressure (84 +/-
3 mmHg before and 86 +/- 3 mmHg after propranolol). Arterial plasma
norepinephrine levels rose from 183 +/- 20 to 250 +/- 29 pg/ml during
propranolol (P less than 0.001), suggesting increased sympathetic
vasoconstrictor tone. However, isotope dilution studies using tritiated
norepinephrine infusion showed that arterial plasma levels of tritiated
norepinephrine rose from 743 +/- 78 to 1,002 +/- 101 dpm/ml during
propranolol (P less than 0.001), indicating a reduction in the rate of
norepinephrine clearance from plasma. The calculated fall in clearance from
1.90 +/- 0.13 to 1.42 +/- 0.11 1/min (P less than 0.001) entirely accounted
for the rise in plasma norepinephrine, since the calculated rate of
norepinephrine spillover into plasma remained at the base-line level of 340
+/- 40 ng/min during propranolol. In control studies on four subjects,
arterial plasma norepinephrine levels and norepinephrine kinetics did not
change from base line during the control period. We conclude that
maintenance of blood pressure during propranolol infusion is not due to a
reflex generalized increase of sympathetic vasoconstrictor tone.
