Osmotic and metabolic responses to dehydration and urea-loading in a terrestrially-hibernating frog

by Muir, Timothy James.

OSMOTIC AND METABOLIC RESPONSES TO DEHYDRATION AND UREA- LOADING IN A TERRESTRIALLY-HIBERNATING FROG Timothy James Muir Physiological responses to dehydration in amphibians are reasonably well documented, although little work has addressed this problem in hibernating animals. We investigated osmotic and metabolic responses to experimental manipulation of hydration state in the wood frog (Rana sylvatica). In winter-conditioned frogs, plasma osmolality varied inversely with body water content primarily due to increases in sodium and chloride concentrations, as well as de novo synthesis of glucose and urea. Decreased hydration was accompanied by a marked reduction in the resting rate of oxygen consumption, which was inversely correlated with plasma osmolality and urea concentration. Resting rates of oxygen consumption in fully-hydrated frogs receiving injections of saline or saline containing urea did not differ initially; however, upon dehydration, metabolic rates decreased sooner in the urea-loaded frogs than in control frogs. Our findings suggest an important role for urea, acting in concert with dehydration, in the metabolic regulation of hibernating R. sylvatica.