AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 2 292-R297, Copyright © 1987 by American Physiological Society
Organ-specific metabolism during freezing and thawing in a freeze-tolerant frog
K. B. Storey
Freeze-tolerant wood frogs, Rana sylvatica, were exposed to three
consecutive freeze-thaw cycles. Each 2-day freezing exposure resulted in
the breakdown of liver glycogen and an accumulation of high quantities of
glucose in all 10 tissues tested; during each 2-day thaw glucose was
restored as liver glycogen. The data suggest that frogs do not maintain
cryoprotectants throughout the winter in anticipation of freezing but only
synthesize and/or maintain glucose during actual freezing episodes. The
pattern of glucose accumulation during freezing suggests a peripheral
vasoconstriction as freezing progresses, leaving circulation open to
central organs (liver, heart, and brain) for as long as possible. Lactate
and alanine contents in tissues rose during each freezing exposure and were
reduced during each thaw. Based on anaerobic end-product accumulation,
organs appeared to vary up to 10-fold in anaerobic energy requirements in
the frozen state. Levels of adenylates and fructose-2,6-biphosphate were
measured in liver and muscle and provided additional evidence of
tissue-specific differences in metabolism in the frozen state.
