Effects of vagal blockade on the counterregulatory response to
insulin-induced hypoglycemia in the dog.
Jackson, P. A., M. J. Pagliassotti, M. Shiota, D. W. Neal, S. Cardin,
and A. D. Cherrington.
Department of Molecular Physiology and Biophysics, Vanderbilt
University School of Medicine, Nashville, TN 37232-0615
APStracts 4:0200E, 1997.
Our aim was to determine if vagal transmission is required for the
hormonal response to insulin-induced hypoglycemia in 18-hour fasted,
conscious dogs. Hollow coils were placed around the vagus nerves
under general anesthesia two weeks prior to an experiment. On the day
of the study they were perfused with -15 degrees C ethanol for the
purpose of blocking vagal transmission either coincident with the
onset of insulin- induced hypoglycemia or after 2h of established
hypoglycemia. In a separate study the coils were perfused with 37
degrees C ethanol in a sham cooling experiment. The following
parameters were measured: heart rate, arterial plasma glucose,
insulin, pancreatic polypeptide, glucagon, cortisol, epinephrine,
norepinephrine, glycerol, free fatty acids as well as endogenous
glucose production. In response to insulin-induced hypoglycemia (42
mg/dl), plasma glucagon peaked at a level that was double the basal
level and plasma cortisol levels quadrupuled. Plasma epinephrine and
norepinephrine levels both rose considerably to 2135 +/- 314 and 537
+/- 122 pg/ml respectively as did plasma glycerol (330 +/- 60%) and
endogenous glucose production (150 +/- 20 %). Plasma free fatty acids
peaked at 150 +/- 20% and then returned to basal levels by the end of
the study. The hypoglycemia-induced changes were not different when
vagal cooling was initiated after the prior establishment of
hypoglycemia. Similarly, when vagal cooling occurred concurrently
with the initiation of insulin-induced hypoglycemia (46 mg/dl), there
was no significant differences in any of the parameters measured as
compared to the control. Thus, vagal blockade did not prevent the
effect on either the hormonal or metabolic responses to low blood
sugar. Functioning vagal afferent nerves are not required for a
normal response to insulin-induced hypoglycemia.
Received 22 January 1997; accepted in final form 11 September
1997.
APS Manuscript Number E35-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997