Cell volume regulation in juveniles of xenopus laevis in hypertonic urea solution

Regulation of body water balance in reedfrogs (superspecies Hyperolius viridiflavus and Hyperolius marmoratus: Amphibia, Anura, Hyperoliidae) living in unpredictably varying savannah environments

The regulation of body water balance was examined in the reedfrogs Hyperolius marmoratus taeniatus and Hyperolius viridiflavus ommatostictus. Temperature and stage of post-metamorphic development significantly affected the rate of water uptake. Hydrated reedfrogs prevented hyperhydration by voiding diluted urine when obtaining water. Within 48 hr after rehydration, body fluid osmolality remained at low levels, which may be supportive to counter excessive cutaneous water influx in hydrated frogs. Once evaporative water loss exceeded 10-12% total body mass, reedfrogs became anuric. The rate of water uptake strongly increased with increasing body water deficit. Both the anuric response and the increased rate of water uptake are assumed to strongly enhance the efficacy of using very briefly available water sources during dry-period conditions. Dry-adapted and estivating reedfrogs survived evaporative water losses between 40 and 55% total body mass. Bladder fluid stores contributed substantially to this desiccation tolerance. During a 16-day period of desiccation, H. v. ommatostictus could replace approximately 25% of evaporative water loss from the bladder fluid store. During desiccation, the level of free amino acids selectively increased in the gastrocnemius muscle tissue, which may support cell volume regulation and/or protect cellular structures from osmotic stresses. Even strongly dehydrated reedfrogs rehydrated quickly with no obvious osmoregulatory problem. Rehydration was associated with a higher than expected decrease of free amino acids in the gastrocnemius muscle tissue, a response that may help to protect cells from bursting during fast rehydration.

Urea tolerance and osmoregulation in Bufo viridis and Rana ridibunda

1. The tolerance and adaptation to urea solutions by terrestrial green toads (Bufo viridis) and semi-aquatic frogs (Rana Ridibunda) were studied. 2. the green toad showed tolerance to urea solution of 800 mM and the frogs showed tolerance only to about 400 mM urea solution. 3. The plasma concentrations of both species was hyperosmotic to the external medium in all the different urea solutions. 4. Blood osmolality, urea, Na+ and Cl- concentrations of B. viridis were always higher than in R. ridibunda. 5. The urea concentration in muscle of R. ridibunda was higher than the urea concentration in muscle of B. viridis. 6. The muscle tissue weight loss of B. viridis was significantly lower than R. ridibunda.