AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 6 1446-R1454, Copyright © 1991 by American Physiological Society
Nonshivering thermogenesis in king penguin chicks. II. Effect of fasting
C. Duchamp, H. Barre, J. L. Rouanet, A. Lanni, F. Cohen-Adad, G. Berne and P. Brebion
Laboratoire de Thermoregulation et Energetique de l'Exercice, Centre National de la Recherche Scientifique, Lyon, France.
The effect of fasting on the energy metabolism of skeletal muscle and liver
was investigated in cold-acclimatized short-term fasting (STF) (3 wk) and
naturally long-term fasting (LTF) (4-5 mo) king penguin chicks, both groups
exhibiting nonshivering thermogenesis (NST). A comparison was made with
nourished cold-acclimatized controls. In these chicks, no brown adipose
tissue deposits could be found on electron-microscopic observations of fat
deposits. Protein content and cytochrome oxidase (CO) activity of tissue
homogenates were measured in liver and pectoralis and gastrocnemius
muscles, as were protein content, CO activity, and respiration rates of
mitochondria isolated from these organs. Fasting-induced protein loss
affected the pectoralis more than the gastrocnemius muscle, thus preserving
locomotor function. In STF chicks, specific mitochondrial protein content
and specific tissue CO activity were preserved but total organ CO capacity
was reduced by half in pectoralis and liver following the fall in organ
mass. In LTF chicks, both specific and total CO activity were drastically
reduced in muscles, whereas specific CO activity was preserved in liver. In
these LTF chicks, muscle mitochondria showed an energized configuration
associated with an increased area of inner membrane in gastrocnemius. A
reduction of respiratory control ratio (RCR) was observed in subsarcolemmal
muscle mitochondria of STF chicks, whereas intermyofibrillar and liver
mitochondria kept high RCR values.(ABSTRACT TRUNCATED AT 250 WORDS)
