AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 5 1350-R1355, Copyright © 1994 by American Physiological Society
Intracerebroventricular insulin produces nonuniform regional increases in sympathetic nerve activity
M. S. Muntzel, D. A. Morgan, A. L. Mark and A. K. Johnson
Department of Psychology, University of Iowa, Iowa City.
Insulin has been shown to increase sympathetic nerve activity (SNA).
Although it has been proposed that insulin acts within the central nervous
system (CNS) to increase sympathetic neural outflow, there is little
evidence for direct central neural sympathoexcitatory effects of insulin.
To determine whether intracerebroventricular insulin elicits increases in
peripheral SNA, we infused insulin (0.1 microU/min, low; 10 microU/min,
medium; and 100 microU/min, high doses) or artificial cerebrospinal fluid
(aCSF) into the third cerebral ventricle of chloralose-anesthetized Wistar
rats while recording lumbar SNA. In separate animals, 10 microU/min of
insulin were infused while recording adrenal SNA and renal SNA. Blood
glucose and plasma insulin levels did not significantly change during
intracerebroventricular infusion of insulin. Lumbar SNA, expressed as
percentage of baseline, did not change in rats infused with aCSF (+ 13% +/-
8%) but increased significantly in rats infused with low (+ 72 +/- 17%),
medium (+ 119 +/- 30%), and high (+ 113 +/- 25%) doses of insulin (P <
0.05). Intracerebroventricular insulin failed to significantly increase
adrenal SNA or renal SNA. Blood pressure and heart rate did not change
during insulin infusion. The results indicate that administration of
insulin into the third cerebral ventricle produces regionally nonuniform
increases in sympathetic neural outflow in the absence of changes in blood
glucose or plasma insulin.
