AJP - Endocrinology and Metabolism, Vol 246, Issue 6 465-E470, Copyright © 1984 by American Physiological Society
Glucoregulatory and metabolic responses to heat exposure in rats
R. Chayoth, A. F. Nakhooda, P. Poussier and E. B. Marliss
To determine the possible role of altered secretion and effects of insulin
in fuel homeostasis during heat exposure, the hormonal and metabolic milieu
of three groups of rats were studied. The first was placed at 35 degrees C
for 12 days (HE), the second was pair-fed (PF) to the first but maintained
at 23 degrees C, and the third was allowed to eat ad libitum at 23 degrees
C (C). Plasma insulin, glucagon, glucose, and free fatty acids (FFA), and
blood lactate, pyruvate, 3-hydroxybutyrate, and individual amino acids were
determined. To further characterize glucoregulation, an intraperitoneal
glucose tolerance test (1 mg/g body wt) and isotopic glucose turnover
(primed infusion of [3-3H]glucose) were performed. In HE rats, weight was
constant for the last third of the period, and metabolic state 4 h after
food removal was characterized by euglycemia but hypoinsulinemia, elevated
blood pyruvate and FFA, and normal 3-hydroxybutyrate compared with C.
Lowered levels of branched-chain amino acids and arginine were found.
Fourteen hours after food removal glucose turnover was decreased. However,
glucose intolerance accompanied by hyperinsulinemia was also found. Many of
these changes were also seen in PF, including constant weight, fasting
euglycemia, hypoinsulinemia, elevated FFA, and lowered valine and
isoleucine. In contrast, pyruvate concentrations were normal, that of
3-hydroxybutyrate was elevated, and the decrement in glucose turnover was
smaller than in HE rats. The glucose tolerance was similar to that of HE
but accompanied by hypoinsulinemia. The results in HE suggest decreased
energy metabolism, insulin secretion altered in a complex manner, and
altered insulin action.(ABSTRACT TRUNCATED AT 250 WORDS)
