Nitrogenous Waste Handling by Larval ZebrafishDanio rerioin Alkaline Water

Abstract

Although adult fish excrete their nitrogenous waste primarily as ammonia, larval fish may excrete a higher proportion as urea, an evolutionary strategy that lessens nitrogenous waste toxicity during early development. Previous studies firmly established that ammonia excretion is inhibited in adult fish acutely exposed to alkaline water. This study was designed to test the hypothesis that total nitrogen excretion is maintained in larval zebrafish raised in alkaline water (pH ∼ 10.0) as a result of compensatory adjustments to urea and/or ammonia transport pathways. Raising zebrafish in alkaline water from 0 to 4 d postfertilization (dpf) reduced ammonia excretion at 4 dpf, whereas urea excretion was elevated by 141%. The increase in urea excretion at 4 dpf served to maintain total nitrogen excretion constant, despite the persistent inhibition of ammonia excretion. Whole body ammonia and urea contents were not significantly altered by exposure to alkaline water. Protein and mRNA expression of Rhcg1, an apically expressed ammonia-conducting channel, were significantly elevated after 4-d exposure to alkaline water, whereas the mRNA expression of Rhag, Rhbg, and urea transporter were unaffected. The acute exposure to alkaline water of 4-dpf larvae reared in control water caused a rapid inhibition of ammonia excretion that had partially recovered within 6 h of continued exposure. The partial recovery of ammonia excretion despite continued exposure to alkaline water suggested an increased ammonia excretion capacity. In agreement with an increased capacity to excrete ammonia, the transfer of larvae back to the control (normal pH) water was accompanied by increased rates of ammonia excretion. Urea excretion was not stimulated during 6-h exposure to alkaline water. Following both chronic and acute exposure to alkaline water, the rate of uptake of methylamine (an ammonia analog) was significantly elevated, consistent with increased protein expression of the apical ammonia channel, Rhcg1. Taken together, this study demonstrates a complex interplay between ammonia and urea excretion in larval zebrafish exposed to alkaline water.

Metabolomic profiling of zebrafish (Danio rerio) embryos exposed to the antibacterial agent triclosan

“…The up‐regulation of L‐glutamic acid in zebrafish embryos exposed to 300 μg/L triclosan embryos in the present study may be related to a change in the gamma‐aminobutyric acid system, which also reflects damage in brain development (Santos‐Fandila et al ). This is consistent with previous studies showing that cholinesterase activity can be significantly elevated in zebrafish exposed to triclosan (Oliveira et al ) and that triclosan‐exposed zebrafish exhibit gene expression changes in the brain and apoptosis in neuronal cells (Kumai et al ; Szychowski et al ). However, the results of one study have conversely demonstrated that triclosan is a very weak nonneurotoxin (Muth‐Kohne et al ).…”

“…The generation of urea provides insight into fish nitrogen balance and has been reported to be a useful marker for environmental stress in fish. Although adult fish mainly excrete their nitrogenous waste as ammonia, zebrafish embryos and larvae excrete approximately 80% of nitrogenous waste as urea, using the urea transporters as a tool to efficiently cross plasma membranes (Braun et al , ; Kumai et al ). In the present study, we observed increased urea levels in zebrafish embryos exposed to triclosan.…”

Transcriptomic and proteomic analyses provide insights into the adaptive responses to the combined impact of salinity and alkalinity in Gymnocypris przewalskii

“…NH 4 + and HCO 3 − can be used to produce urea in the liver for acid–base homeostasis (Weiner and Verlander 2016 ). Upregulation of Tgm5 probably takes effect by promoting NH4 + transportation as glutamine after NH 3 incorporation to achieve acid–base homeostasis (Kumai, et al 2015 ; Wang, et al 2003 ; Yao, et al 2016 ).…”

BSA/ASN/Pol407 nanoparticles for acute lymphoblastic leukemia treatment

“…Also, in embryos, ammonia excretion is limited by the chorion so fish must detoxify ammonia by synthesizing urea [36,37]. All this similarities with mammals could be an indication of how zebrafish embryos could be used as a model to study the nanoparticles capacity to retain ammonia [38,39].…”