AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 5 1463-R1469, Copyright © 1994 by American Physiological Society
Effect of intrahypothalamic insulin on sympathetic nervous function in rats drinking a high-sucrose solution
J. P. Porter
Department of Physiology, University of Louisville, Kentucky 40292.
Hyperinsulinemia has been associated with increased sympathetic nervous
activity. However, direct injection of insulin into the hypothalamus of
anesthetized rats produces sympatho-inhibition. This discrepancy could be
due to confounding effects of anesthesia or insulin resistance on central
neural function. The effect of injecting saline or insulin (3.0 or 30 mU)
into the ventromedial hypothalamus on mean arterial pressure, heart rate,
and renal nerve activity (RNA) was investigated in conscious rats and in
rats anesthetized with urethan or pentobarbital. Insulin decreased RNA in
conscious rats but had no effect in pentobarbital-anesthetized rats. In
urethan-anesthetized rats with hyperglycemia, the insulin increased RNA.
Drinking a 10% sucrose solution enhanced the sympathoexcitatory effect of
insulin in the urethan-anesthetized rats but had no effect in the other two
groups. The sucrose solution did not affect insulin sensitivity in any
group; however, urethan anesthesia did produce insulin resistance. These
data show that central effects of insulin are sensitive to anesthesia and
do not support a sympathoexcitatory role for insulin in the ventromedial
hypothalamus of conscious rats, at least in relation to the renal
sympathetic nerves.
