Ammonia excretion in the Atlantic hagfish, (Myxine glutinosa)

The hagfishes possess the longest known evolutionary history of the extant craniates and likely offer exclusive insight into vertebrate origins. The Atlantic hagfish is physiologically adapted to spend much of its life burrowed in ocean-floor substrate and marine carcasses, where unfavorable conditions for ammonia excretion are likely encountered. Plasma ammonia concentrations were experimentally elevated by injection of NH4Cl. Ammonia excretion rates and plasma ammonia concentrations were measured. Expression of Rhcg and Rhbg mRNA was quantified using quantitative RT-PCR. We present evidence that suggests Atlantic hagfish are capable of reducing experimentally elevated plasma ammonia concentrations and eventually eliminating the plasma ammonia load within 12 hours. Following the injection of ammonia elevated plasma ammonia concentrations paralleled elevated ammonia excretion rates and coincided with the initial upregulation of Rhcg and Rhbg in the gill and Rhcg in the skin suggesting that the transcriptional regulation of Rh glycoproteins may respond, in part, to elevated plasma ammonia.