METABOLIC EFFECTS OF DEHYDRATION ON AN AQUATIC FROG, RANA-PIPIENS

Cellular responses to dehydration were analyzed in six organs of leopa rd frogs Rana pipiens. Frogs at 5 degrees C endured the loss of up to 50 % of their total body water content but water contents of individua l organs were strongly defended, Skeletal muscle water content was str ongly affected by dehydration, dropping from 80.7 % of wet mass in con trols to 67.2 % in frogs that had lost 50 % of their total body water, However, water contents of internal organs dropped by only 3-8 % of t heir wet masses, Water contents of ah organs except skeletal muscle we re fully restored by 24h of rehydration in water at 5 degrees C, Dehyd ration had no consistent effect on the protein content of five organs but in a sixth, the kidney, protein levels were elevated (by 60-72 %) at the higher levels of dehydration and during rehydration, Dehydratio n led to a rapid increase in glucose concentration in the liver; compa red with control values of 13+/-2 nmol mg(-1) protein, levels were dou bled by 12.2 % dehydration and continued to increase to a maximum of 3 07+/-44 nmol mg-l protein (20 mu mol g-l wet mass) in 50 % dehydrated frogs, Glucose accumulation was supported by a decrease in liver glyco gen content and a parallel rise in glucose 6-phosphate levels, but not in the levels of other glycolytic intermediates, confirming that glyc ogenolytic flux was being directed into glucose synthesis, Blood gluco se levels also increased as a function of increasing dehydration, reac hing values 13.8 times higher than controls, but only the kidney and b rain showed a significant accumulation of glucose over the course of d ehydration, All organs (except skeletal muscle) had increased lactate levels during dehydration, particularly at 36.6 and 50 % dehydration, Severe dehydration also compromised cellular energetics, with ATP leve ls dropping by 44 % in liver of 50 % dehydrated frogs, However, frogs readily recovered from dehydration stress and, after rehydration for 2 4 h, organ lactate levels were sharply reduced relative to 50 % dehydr ated frogs and liver energy status was largely restored, The hyperglyc aemic response elicited by dehydration in this semi-aquatic frog mirro rs the extreme hyperglycaemia seen in freeze-tolerant frogs during com parable dehydration exposure at 5 degrees C or during freezing, This s uggests that the cryoprotectant response of freeze-tolerant species ma y have grown out of a pre-existing hyperglycaemic response to dehydrat ion, a common stress experienced by all anurans,