AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 6 1370-R1376, Copyright © 1989 by American Physiological Society
Paraventricular nucleus modulation of glycemia and insulinemia in freely moving lean rats
E. Ionescu, C. C. Coimbra, C. D. Walker and B. Jeanrenaud
Laboratoires de Recherches Metaboliques, Faculty of Medicine, University of Geneva, Switzerland.
The effect of norepinephrine (NE) injection (40 nmol) into the
paraventricular nucleus (PVN) on plasma insulin and glucose levels was
studied in freely moving lean Zucker rats bearing chronic right jugular
catheters for blood sampling and unilateral intracerebral cannulas placed
just above the PVN. Already 2.5 min after NE injection, plasma glucose
levels rose significantly, reaching a peak at 10 min poststimulus, whereas
the insulin output was strongly inhibited. This NE-induced hyperglycemia
was independent of the corticosterone levels. A ganglionic blockade
performed by intravenous chlorisondamine (1 mg/kg body wt) reduced by 80%
the 4.5-min NE-induced incremental glucose areas. NE-induced hyperglycemia
was reduced to a large extent when the PVN alpha-adrenergic receptors were
blocked with phentolamine and to a lesser extent when the beta-adrenergic
receptors were blocked with propranolol. NE-induced inhibition of insulin
output was not affected by these adrenergic blockers. It is concluded that,
when administered locally into the PVN, NE can activate the sympathetic
outflow expressed by a neurally mediated hyperglycemia through central
alpha- and beta-adrenoreceptor and an inhibition of insulin output through
other types of receptors and/or mechanisms.
