Metal toxicity in the spotted dogfish Scyliorhinus canicula

Abstract

In most vertebrate groups high levels of urea in the plasma are not tolerated. However, elasmobranchs have adapted a variety of mechanisms to counteract the potential harmful effects of the high concentration of urea (>300 mM) in their plasma. One such method is the retention of methylamines that counteract the toxicity of urea, the most notable of which is trimethylamine oxide (TMAO). A customary method for measurement of TMAO involves the reduction of TMAO to TMA followed by the extraction and analysis of the amine in its picrate form (Wekell and Barnett, 1991). In the alternative method TMAO was measured by ion exchange chromatography (Metrhom Peak). Briefly, plasma samples from the little skate, Raja erinacea, (10 ml) were diluted with 10 ml of MilliQ water and injected onto a cation exchange column (Metrosep 2-150) using a mobile phase of 4 mM tartaric acid and 0.75 mM dipicolinic acid at a flow rate of 1 ml min−1. Cation detection was achieved using a Metrohm Peak IC 819 detector. TMAO was measured in the same samples using the method first described by Wekell and Barnett (1991) and results were found to be comparable. Additional methylamines and b-amino acids did not interfere with the measurement of TMAO and under these conditions TMAO did not interfere with the measurement of other ions from the same sample. This method was advantageous because; much less sample was required for measurement; there was no requirement for strong solvents; and multiple cations were measured from the same sample. Wekell and Barnett (1991), J. Food Sci. 56, 132–135. Email Address for correspondence: andersow@cc.umanitoba.ca