Meeting Abstract
P1.58 Thursday, Jan. 3 Urea-Induced Metabolic Depression Varies Seasonally in Isolated Organs of the Wood Frog MUIR, T.J.*; COSTANZO, J.P.; LEE JR, R.E.; Miami University Muirtj@muohio.edu
Animals faced with adverse environmental conditions often undergo periods of extended dormancy characterized by a substantial metabolic depression. Several species from diverse taxa accumulate urea during those times, and it has long been suspected that urea plays a key role in the induction or maintenance of the metabolic suppression. However, little evidence supporting that hypothesis in living systems exists. We measured aerobic metabolism in the presence or absence of 80 mM urea of isolated heart, liver, muscle, skin, and stomach from the wood frog (Rana sylvatica), a terrestrial hibernator that accumulates urea in fall and winter. We did these tests using frogs acclimatized to spring, summer, or winter and at varied temperatures. No metabolic effect of urea was found in organs from summer frogs at 20°C or winter frogs at 4°C. However, urea significantly reduced metabolism in heart, liver, and stomach from spring frogs at 4°C by 35, 10, and 20%, respectively. Additionally, liver, muscle, and stomach from winter frogs had significantly lower metabolic rates (by 15, 50, and 20%, respectively) in the presence of urea at 10°C. Removal of urea from muscle of winter frogs reversed the metabolic inhibition, suggesting the depression was directly caused by urea�s presence. Because muscle and liver together account for such a large proportion of the anuran body, it is likely that this inhibitory effect of urea on the metabolic rate would translate to a substantial metabolic depression in the intact frog. Moreover, the apparent reversal of metabolic suppression upon the removal of urea may contribute to arousal from hibernation in the spring when urea levels plummet. Our findings have a potentially wide-ranging impact due to the number of diverse organisms that accumulate urea during dormancy. Supported by NSF grant: IOB 0416750.
