AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 2 265-R271, Copyright © 1983 by American Physiological Society
Seasonal acclimatization in American goldfinches: the role of the pectoralis muscle
M. E. Yacoe and W. R. Dawson
The present study attempts to assess whether the marked seasonal changes in
the capacity for shivering thermogenesis in American goldfinches (Carduelis
tristis) involve adjustments of metabolic pathways of the pectoralis
muscles similar to those observed in mammalian muscle in response to
endurance training, i.e., changes favoring increased reliance on fatty acid
oxidation and decreased utilization of carbohydrate reserves. Analysis of
seasonal changes in enzyme profile of the pectoralis muscle revealed that
winter-acclimatized birds have significantly greater (P less than 0.05)
activities of phosphorylase, phosphofructokinase, and beta-hydroxy-acyl-CoA
dehydrogenase than do birds in other seasons. The activities of citrate
synthase and hexokinase do not vary seasonally. These results differ
fundamentally from the pattern of changes in enzyme activities associated
with endurance adaptation in mammals. Furthermore no seasonal changes were
observed in capacities for the oxidation of fatty acids (palmitate and
linoleate) or pyruvate in either crude homogenates or isolated mitochondria
of goldfinch pectoralis muscles. The oxidation of pyruvate by isolated
pectoralis muscle mitochondria was inhibited (greater than 90%) by the
oxidation of palmitoyl carnitine at palmitoyl carnitine concentrations as
low as 50 microM. These data agree with physiological observations
indicating little use of glucose by this tissue during steady-state
shivering. However, the extent of this inhibition does not vary seasonally.
Therefore the present study fails to document any significant seasonal
change in the catabolic pathways of the pectoralis muscle that would link
observed seasonal changes in capacity for shivering thermogenesis with a
shift in the balance of substrate use by this tissue.
