Renal Conservation of Trimethylamine Oxide by the Spiny Dogfish, Squalus Acanthias

Abstract

Trimethylamine oxide (Oxide) plasma concentrations in the dogfish have been found to be maintained within the narrow range of 60–80 µmol/ml. These levels are maintained in spite of prolonged (up to 41 days) fasting. The Oxide is freely filterable at the glomerulus but is avidly reabsorbed by the renal tubule. Thus, less than 10% of the filtered Oxide appears in the urine. Dogfish urine has been found to contain an unidentified volatile amine, not NH₃, presumed to be trimethylamine. The possible role of the Oxide in elasmobranch physiology is discussed.