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 as sessed for both fall- and spring-collected spring peepers Psuedacris c rucifer. Frogs readily endured the loss of 50% of total body water. Du ring dehydration organ water content was defended with no change in wa ter content in skeletal muscle, gut, and kidney of 50% dehydrated frog s and reduced water content in liver, brain and heart. Dehydration sti mulated a rapid and massive increase in liver glucose production. In f all-collected frogs liver glucose rose by 120-fold to 2690 +/- 1400 nm ol.mg protein(-1) or 220 mu mol.g ww(-1) in 50% dehydrated frogs and g lucose in other organs increased by 2.6- to 60-fold. Spring-collected frogs showed the same qualitative response to dehydration although abs olute glucose levels were lower, rising maximally by 8.4-fold in liver . Glucose synthesis was supported by glycogenolysis in liver and chang es in the levels of glycolytic intermediates in liver indicated that a n inhibitory block at the phosphofructokinase locus during desiccation helped to divert hexose phosphates into the production of glucose. Li ver energy status (ATP, total adenylates, energy charge) was maintaine d even after the loss of 35% of total body water but at 50% dehydratio n all parameters showed a sharp decline; for example, energy charge fe ll from about 0.85 to 0.42. Severe dehydration also led to an accumula tion of lactate in four organs, probably hypoxia-induced due to impair ed circulation, The hyperglycemic response of P. crucifer to dehydrati on mimics the cryoprotectant synthesis response seen during freezing o f this freeze-tolerant frog, suggesting that these share a common regu latory mechanism and that the cryoprotectant response may have arisen out of pre-existing volume regulatory responses of amphibians. The hyp erglycemic response to dehydration might also be utilized during winte r hibernation to help retard body water loss by raising the osmolality of the body fluids in situations where hibernaculum conditions become dry,