Effects of dehydration on organ metabolism in the frog Pseudacris crucifer: hyperglycemic responses to dehydration mimic freezing-induced cryoprotectant production.
The metabolic effects of evaporative water loss at 5 degrees C were assessed for both fall- and spring-collected spring peepers Pseudacris crucifer. Frogs readily endured the loss of 50% of total body water. During dehydration organ water content was defined with no change in water content in skeletal muscle, gut, and kidney of 50% dehydrated frogs and reduced water content in liver, brain and heart. Dehydration stimulated a rapid and massive increase in liver glucose production. In fall-collected frogs liver glucose rose by 120-fold to 2690 +/- 400 nmol.mg protein-1 or 220 mumol.g ww-1 in 50% dehydrated frogs and glucose in other organs increased by 2.6- to 60-fold. Spring-collected frogs showed the same qualitative response to dehydration although absolute glucose levels were lower, rising maximally by 8.4-fold in liver. Glucose synthesis was supported by glycogenolysis in liver and changes in the levels of glycolytic intermediates in liver indicated that an inhibitory block at the phosphofructokinase locus during desiccation helped to divert hexose phosphates into the production of glucose. Liver energy status (ATP, total adenylates, energy charge) was maintained even after the loss of 35% of total body water but at 50% dehydration all parameters showed a sharp decline; for example, energy charge fell from about 0.85 to 0.42. Severe dehydration also led to an accumulation of lactate in four organs, probably hypoxia-induced due to impaired circulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Churchill
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Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada.
Storey
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D000818:Animals; D001001:Anura / Q000378:metabolism*; D001834:Body Water / Q000378:metabolism; D003451:Cryoprotective Agents / Q000378:metabolism*; D003681:Dehydration / Q000150:complications* / Q000378:metabolism*; D005615:Freezing; D006943:Hyperglycemia / Q000209:etiology* / Q000503:physiopathology*; D011506:Proteins / Q000378:metabolism; D012621:Seasons
D003451:Cryoprotective Agents; D011506:Proteins