AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 6 1035-R1040, Copyright © 1988 by American Physiological Society
Insulin secretion and substrate homeostasis in prolonged hypothermia in rats
R. Hoo-Paris, M. L. Jourdan, L. C. Wang and R. Rajotte
Department of Zoology, University of Alberta, Edmonton, Canada.
In hypothermia, impairment of metabolic substrate mobilization and
utilization may be a factor limiting survival. By use of a newly developed
technique, substrate profiles and their regulation by insulin were examined
in hypothermic rats (body temperature 19 degrees C) over 24 h. Plasma
glucose concentrations increased to approximately 300 mg/dl during cooling
and remained high throughout the period of hypothermia. Free fatty acid
(FFA) concentration was not altered during cooling or during the first 10 h
of hypothermia (approximately 700 mu eq/l) but progressively decreased
thereafter, reaching 420 mu eq/l by 20 h. Plasma insulin decreased
dramatically during cooling and remained very low (9 +/- 2 microU/ml)
during the whole period of hypothermia, reflecting the suppression of
insulin secretion by isolated islets at low temperatures. To test he
hypothesis that suppression of endogenous insulin secretion may hamper
glucose utilization and thus limit survival in hypothermia, exogenous
insulin was administered. At doses of 0.1, 0.5, and 1 U/kg intravenously,
insulin slowly decreased plasma glucose and FFA. However, at 0.1 and 1 U/kg
intraperitoneally, insulin resulted in a dose-dependent decrease in
survival time in the hypothermic rat. It is possible that the antilipolytic
effect of insulin may have outweighed any beneficial effect of improving
glucose utilization in hypothermia.
