Intrarenal control of urea reabsorption by renal tubules of the marine elasmobranch, Squalus acanthias

Abstract

1. 1. Exogenous epinephrine caused a fifteen-fold increase in urea elimination expressed as fraction of filtered load excreted, while urine flow rates doubled and the excretion of chloride and trimethylamine oxide increased 2·6 and 3·8-fold, respectively. 2. 2. Expansion of extracellular fluid volume by 20 per cent caused an eightfold increase in the fractional excretion of urea. 3. 3. The osmoregulatory significance of tubular control was further indicated by a 40 per cent rise in the fraction of filtered urea excreted when dogfish were maintained in a hypotonic 70 per cent sea water environment. 4. 4. Extraglomerular control mechanisms appear to be implicated in each of these experimental situations.