AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 5 563-R569, Copyright © 1982 by American Physiological Society
Substrate metabolism in seasonally acclimatized American goldfinches
R. L. Marsh and W. R. Dawson
Concentration of ([Glc]) and turnover (Ro) of plasma glucose, concentration
of free fatty acids in plasma ([FFA]), and concentration of glycogen in
muscle and liver were measured in freshly captured summer- and
winter-acclimatized American goldfinches (Carduelis tristis). These birds
were acutely exposed to one of three thermal regimes: 1) "thermoneutral,"
30 degrees C in air, 2) "cold," -15 degrees C in air, and 3) "severe cold,"
0 degrees C in 79% He and 21% O2. Additionally, the activities of citrate
synthase (CS), phosphofructokinase (PFK), and beta-hydroxyacyl-CoA
dehydrogenase (HOAD) were measured in pectoralis and leg muscles of winter
and summer birds. Ro for goldfinches at 30 degrees C is unchanged between
winter and summer, whereas it is 25% lower at -15 degrees C in winter than
in summer birds, even though rates of heat production are similar.
Additionally, winter animals depleted muscle glycogen at slower rates than
summer individuals when exposed to "cold" or "severe cold." [Glc] and [FFA]
for each test regime did not vary between seasons. The activity of the
beta-oxidative enzyme HOAD is the pectoralis muscle (the main thermogenic
tissue) increases by 50% from summer to winter, but the activities of PFK
and CS remain essentially constant. We conclude that the ability to
restrict carbohydrate use under cold stress is a component of the winter
acclimatization process in the American goldfinch. One mechanism which
might foster this ability in the increase in beta-oxidative capacity of the
flight muscles, permitting a greater reliance on fatty acids by winter
animals during cold-induced thermogenesis.
