AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 4 883-R887, Copyright © 1993 by American Physiological Society
Unaltered cerebral blood flow during hypoglycemic activation of the sympathochromaffin system in humans
W. J. Powers, P. J. Boyle, I. B. Hirsch and P. E. Cryer
Department of Neurology and Radiology, Washington University School of Medicine, St. Louis 63110.
To determine if increases in plasma epinephrine and norepinephrine caused
by hypoglycemia are associated with increments in cerebral blood flow
(CBF), we measured CBF with positron emission tomography in normal humans
at ambient fasting arterial plasma glucose levels and at clamped plasma
glucose levels of 5.3, 3.5, and 2.8 mmol/l using the hyperinsulinemic,
stepped hypoglycemic clamp technique. Despite significant increases in
plasma epinephrine to 7,340 +/- 350 (SE) pmol/l and in plasma
norepinephrine to 3.32 +/- 0.35 nmol/l, mean hemispheric CBF (41 +/- 1, 49
+/- 1, 48 +/- 2, and 51 +/- 3 ml x 100 g-1 x min-1) remained constant at
the ambient (5.2), 5.3, 3.5, and 2.8 mmol/l glycemic levels, respectively.
Furthermore, there was no correlation between CBF and either plasma
epinephrine levels ranging from 160 to 10,580 pmol/l or plasma
norepinephrine levels ranging from 0.56 to 5.10 nmol/l. Failure to
demonstrate any dose-response relationship between plasma catecholamine
levels and CBF argues against their primary role in cerebrovascular control
during hypoglycemia.
