Abstract
SummaryClearances of 14C labelled urea, chemical urea and inulin, were determined under steady-state conditions in the toad Bufo arenarum. Clearances of urea were always lower than those of inulin indicating that urea is reabsorbed. In contrast with Rana catesbiana, the kidney of B. arenarum has a very low level of arginase (1.92 μmoles/min/g of wet tissue), and all the other enzymes of the ornithine cycle are present, with the exception of carbamoyl phosphate synthetase. It is demonstrated that no substantial amount of urinary urea is formed in the kidney of this species. The low level of arginase, in a species which reabsorbs urea passively, strengthens the hypothesis that active transport of urea is related to renal arginase activity.
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